reviewarticle zeolites:promisedmaterialsfor

Hindawi Publishing CorporationISRN Chemical EngineeringVolume 2013 Article ID 907425 19 pageshttpdxdoiorg1011552013907425

Review ArticleZeolites PromisedMaterials forthe Sustainable Production of Hydrogen

Antonio Chica

Instituto de Tecnologiacutea Quiacutemica (UPV-CSIC) Universidad Politeacutecnica de ValenciaAvenida de los Naranjos sn 46022 Valencia Spain

Correspondence should be addressed to Antonio Chica achicaaaaupves

Received 14 November 2012 Accepted 16 December 2012

Academic Editors M J Politi I Poulios and R Sedev

Copyright copy 2013 Antonio Chica is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Zeolites have been shown to be useful catalysts in a large variety of reactions from acid to base and redox catalysis e particularproperties of these materials (high surface area uniform porosity interconnected porechannel system accessible pore volumehigh adsorption capacity ion-exchange ability and shapesize selectivity) provide crucial features as effective catalysts and catalystssupports Currently new applications are being developed from the considerable existing knowledge about these important andremarkablematerials Among them those applications related to the development of processes with less impact on the environment(green processes) and with the production of alternative and cleaner energies are of paramount importance Hydrogen is believedto be critical for the energy and environmental sustainability It is a clean energy carrier which can be used for transportation andstationary power generation In the production of hydrogen the development of new catalysts is one of the most important andeffective ways to address the problems related to the sustainable production of hydrogen is paper explores the possibility to usezeolites as catalysts or supports of catalysts to produce hydrogen from renewable resources Specically two approaches have beenconsidered reforming of biomass-derived compounds (reforming of bioethanol) and water splitting using solar energyis paperexamines the role of zeolites in the preparation of highly active and selective ethanol steam reforming catalysts and their mainproperties to be used as efficient water splitting photocatalysts

1 Zeolites Composition StructureProperties and Applications

Zeolites were rst described in 1756 by the Swedish min-eralogist Cronstedt [1] However the systematic researchefforts on synthetic zeolites were initiated by Barrer in the late1930s [2 3] Barret offered the rst classication of zeolitesbased on molecular size [4] Inspired by the work of Barrerresearchers at UnionCarbide developed synthesis proceduresfor preparation of the rst synthetic zeolites (ie zeolites A and ) that would nd industrial applications [5ndash7]

Initially zeolites were applied as materials for dryingand separation substances Later with the development ofthe concept of acid zeolite catalyst in 1959 they wereused as catalysts in the isomerization of hydrocarbons [8]Previously Houdry et al [9] used them in catalytic cracking

of hydrocarbons Since the development of the rst conceptsto date many business processes based on zeolites as catalystshave been implementede specialization and knowledge ofzeolites have grown so much that the International ZeoliteAssociation (IZA) was founded [10] and currently there arenumerous specialized scientic publications that collect notonly the current knowledge about these materials but alsotheir outstanding commercial application

11 Composition and Structure Zeolites are microporouscrystalline aluminosilicates whose chemical composition isdened by the following general formula [11]

M2119899119899O Al2O3 119909119909 SiO2 and H2O (1)

where M is a metal cation of valence 119899119899 119909119909 119909 2 and 119910119910 119909 119910

2 ISRN Chemical Engineering

F 1 Representation of the projection of the frameworkstructure of zeolites (a) T-site connectivity only (b) ball and stick(c) space lling and (d) (Si Al) O4 tetrahedra

Zeolite framework is formed from corner sharing[SiO4]

4minus and [AlO4]5minus tetrahedra which dene the cavities

and channels in which the cations can be found coordinatingto the framework oxygens andor water molecules Figure 1shows the different representations typical of those used inthe literature of the framework of one zeolite

e ways to combine each tetrahedron are extremelywide e structure of the zeolite is dened by its cornersharing tetrahedra of [SiO4]

4minus and [AlO4]5minus and these are

called secondary building units (SBUs) [12] (see Figure 2)e utility of these constructions is that the angles and

distances of zeolites are contained in these SBUs so thestructural characterization of one zeolite could be carried outby examining the SBUs that it containsere are 16 differentSBUs and the structure of each zeolite can be described usingone or more of these SBUs

In zeolites the organization of TO4 tetrahedra can resultin the formation of rings with different numbers of T atoms(Si Al) e most common rings are 4-T 6-T 8-T 10-T and12-T however zeolitic structures containing 14 18 and 30member rings have been also synthesized [13ndash20]e size ofthemicropores of the zeolite varies depending on the numberof members in the rings between 4 and 12Aring On rings T-O-T angles vary mostly in the range 130∘ndash180∘e exibility ofthis angle is one of the most important factors determiningthe huge variety of existing zeolites

12 Properties Zeolites may act as molecular sieves thusone of their main physical properties is the porosity emicroporous properties of zeolites make them present anextremely large internal surface area in relation to theirexternal surface Micropores are open to the outside allowing

o

o

o o

oo o

o o o

o

o

oo

o o

o ooo

o

o

o o

o

o o

ooo oo o

o

o o

o

o

ooo

oo

o o o o

oo

o

oo

ooo

o o o

o

o oo o

o

o

o o o

o

o

o

o o

o

o

o

o o

oo

o

oo

o o

o

o o

o

o

oo

oo

o

o

o oo o

o

oo

o oo

oo

o

o

o

o

4 6 8 5

4-4 6-6 8-8 6-2

4-1 6-1 5-2 5-1

4-1 4-4-1 5-3 Spiro-5

F 2 Basic secondary units (BSUs) to dene the structure ofzeolites

the transference of matter between the intracrystalline spaceand the surrounding environment

Tridimensional networks of well-dened micropores canact as reaction channels whose activity and selectivity will beenhanced by introducing active sites e presence of strongelectric elds and controllable adsorption properties withinthe pores will produce a unique type of catalyst which byitself can be considered as a catalytic microreactor

e size of the pores and channels of zeolites rangesbetween 4 and 12Aring [21] and the channel system may bemono- bi- or three-directional Table 1 shows the classi-cation of zeolites based on the number of tetrahedrals thatform the pores and give access to the intracrystalline space[22ndash25]

Summarizing the main properties of zeolites are asfollows

(i) high surface area(ii) molecular dimensions of the pores(iii) high adsorption capacity(iv) partitioning of reactantproducts(v) possibility of modulating the electronic properties of

the active sites(vi) possibility for preactivating the molecules when in

the pores by strong electric elds and molecularconnement

13 Applications Zeolites have a variety of industrial applica-tions especially as ion exchangers adsorbents and chemicalscatalysts

ISRN Chemical Engineering 3

T 1 Zeolite classication according to the pore size

Zeolite classication Number of the oxygen atoms in the opening ring Pore diameter () Example of zeolitesSmall pore 8 3 lt 120579120579 lt 120579 Erionite A ITQ-3Medium pore 10 120579 lt 120579120579 lt 120579 ZSM-5 ZSM-11 ITQ-1Large pore 12 120579 lt 120579120579 lt 120579 X Y Beta Ω mordenite ITQ-7 ITQ-21Extralarge pore 18 120579 lt 120579120579 MCM-9 VIP-5 ITQ-33

Zeolites as adsorbents are used in processes of separationand purication of gases and liquids due to their ability toadsorb selectively molecules of different size or polarityeyare used in the separation of oxygen from air to removethe water and CO2 from gas streams separation of thelinear branched hydrocarbons and in the elimination ofvolatile organic compounds from automobile and industrialexhausted gasses [6 26ndash35]

e most important application of zeolites as ionexchangers is the extraction of cations Ca2+ and Mg2+ ofdomestic and industrial waste water [34] Sodium zeolite Ais used in the formulation of detergents to replace polyphos-phates and others highly polluting compoundsey are alsoused in extraction of NH4+ from waste water [33] and theyhave been also used extensively in nuclear waste cleanup (ieaer thereeMile Island and Chernobyl nuclear accidents)

Regarding to the use of zeolites as catalysts or catalystssupports their use is very common in industrial processesof rening petrochemicals and ne chemicals e replace-ment of conventional catalysts in many processes by zeolitesis due to improvements that these materials introduce in thecatalytic activity and selectivity

For the commercial application of zeolites as catalyststogether with a good texture-related properties (area poros-ity) and a high number of active sites zeolites must havegood thermal stability since a large part of catalytic processesare conducted at elevated temperatures Moreover it is veryfrequent that the catalysts used in reactions involving hydro-carbons are deactivated by coke deposits formed during thereactionus they need to be regeneratede regenerationis conducted by burning the coke at temperatures above12057900∘C [36ndash38] e thermal stability of a zeolite dependson the aluminum content AlndashO bonds are weaker than theSindashO one (AlndashO distance is larger than SindashO) therefore thestability depends on aluminum content [39] us in orderto carry out a sufficient number of reaction-regenerationcycles zeolites with high thermal stability are requiredthat is zeolites with SiAl ge 5 [40] ese compositions insome cases can be achieved by direct synthesis (ie Betaand ZSM-5 zeolites) and in other cases in which it is notpossible by direct synthesis it can be achieved by chemical orhydrothermal treatments of synthesized zeolite (ie zeoliteY) [41ndash43]

e substitution of Si by Al together with the correspond-ing compensation cations has another additional effect onthe properties of the zeolites hydrophilicityhydrophobicity[30] e hydrophilic-hydrophobic character has focused onapplications of great practical interestus the hydrophobiczeolites are able to carry out reactions that require absence of

water without the necessity to remove it from the mediumbecause the reaction takes place almost entirely inside thezeolite which being hydrophobic will be water free [44] Forexample silicalite (ZSM-5 structure with SiAl gt 1000) [45]has very low amount of aluminum in such a way that itscrystals (119889119889 119889 119889119889119889 gcc) can oat in the water [46] By contrastzeolite X with high Al content has a pronounced hydrophiliccharacter which permits separating a mixture of oxygen andnitrogen [47] due to the higher quadrupole moment of thenitrogen

e negative charge associated with the tetracoordinatedaluminum is compensated by cations that can be easilyexchanged for other cations by ion exchange processes [48]e exchange of cations is favored by the fact that thecations are not covalently bonded to the structure they areplaced inside the zeolite cavities compensating the defect ofcharge e size and charge of the exchanged cations areimportant variables in the zeolite reactivity Cations of largesize will leave small free spaces in the cavities difficultingthe entrance of reactants is effect is very useful in thosereactions where the selective control is based on geometriceffects [49 50] Among the exchangeable cations that canbe introduced into the zeolite the proton occupies a specialplace e protons are bonded to an oxygen bridge betweenone silicon and one aluminum [51 52] Due to the presenceof channels and cavities of different sizes within the samestructure as well as the existence of nonequivalent positionsthere is a paramount importance to predict minimum energypositions and therefore the location of the exchangeablecations [53] and especially the localization of the protons thatwill determine the activity in acid catalyzed reactions

New scientic applications were considered in the 1980sand 1990s for exploring zeolites as advanced solid state mate-rials Ozin et al [54] considered that zeolites could representa ldquonew frontierrdquo of solid state chemistry with interestingproperties (nanometer dimension window channel and cav-ity architecture) for innovative research and developmentAmong others they consider applications such as molecularelectronics quantum dotschains zeolite electrodes batter-ies nonlinear optical materials and chemical sensors Otherapplications recently reported are related to the use of zeolitesas low k dielectric materials for microprocessors [55]

Future trends in zeolites include (i) discovery of newzeolitic materials (ii) continuous use in petroleum rening(high octane and reformulated gasoline processing of heavycrudes production of diesel and so forth) (iii) use inthe preparation of organic chemical intermediates or end-products and (iv) use in sustainable processes to producebiocompounds and green fuels


Considering the future trends it is quite evident thatzeolites are of great interest for the industry especially dueto the potential they present in elds that are of paramountimportance for the future of our industrialized society suchas raw material transformation environmental pollutioncontrol and energy production and storage

is paper focuses on the application of zeolites forenergy production Specically the use of zeolites in theproduction of hydrogen from renewable energy sourcesis collected biomass (ethanol reforming) and solar (watersplitting)

2 Zeolites for Hydrogen Production

e future energy economy will have an important role forhydrogen (H2) as a clean and CO2-neutral energy source[56] us it has been projected as one of the few long-termsustainable clean energy carriers Currently the synthesisof molecular hydrogen occurs mostly by nonsustainablemethods such as steam reforming (SR) of natural gas orgasication of coal which is associated with the emissionof large quantities of greenhouse gases (GHG) especiallycarbon dioxide (CO2) [57ndash60] us to realize the fullbenets of a hydrogen economy increased energy securitydiverse energy supply and reduced air pollution hydrogenmust be produced cleanly and efficiently from availablerenewable resourcesHydrogen can be produced from renew-able resources (eg biomass and water) using renewableenergy sources (eg sunlight wind wave or hydropower)[61ndash66]

Two important approaches are considered in this paperto produce hydrogen from renewable sources and reduce theCO2 emissions One approach is to apply reforming methodsto biomass-derived compounds for example bioethanolBecause biomass consumes atmospheric carbon dioxide(CO2) during growth it can have a small net CO2 impactcompared with fossil fuels e second approach considersthe production of hydrogen by water splitting using solarenergy Hydrogen production by water splitting correspondsto those methods including outside the C-cycle is processis very attractive due to the potential to use the solar energywhich is very abundant

e use of catalysts to improve the production of hydro-gen by reforming of bioethanol and water splitting has beenreported Among them zeolites seem to have a promisedfuture as catalysts and catalysts supports Here we will reviewrst the use of dierent zeolites in the production of hydrogenby ethanol (or bioethanol) steam reforming We will showthe inuence that the zeolites have as supports to prepareethanol reforming catalysts with high activity selectivity andstability Second we will show the last advances in the use ofthe zeolites to produce hydrogen by water splitting processand the promised future that these materials have by takingadvantage of solar energy

21 Zeolites as Constituents of Catalysts for the SustainableProduction of Hydrogen via EthanolBioethanol ReformingAmong the liquid biomass-derived molecules that can be

used as hydrogen source primary alcohols are interestingcompounds because they can be converted to hydrogen bysteam reforming using moderate reaction conditions emost part of the reforming studies related to alcohols frombiomass is focused on ethanol Ethanol is considered an inter-esting alternative for the sustainable hydrogen productionbecause of (i) its low toxicity (ii) its low production costs (iii)the fact that it is a relative clean fuel in terms of composition(iv) its relatively high hydrogen content (v) its availability andeasiness of handling

Catalytic hydrogen production from ethanol can beperformed by (i) steam reforming (SR) represented by thereaction (2) (ii) partial oxidation (PO) represented bythe reaction (3) and (iii) autothermal reforming (ATR)represented by the reaction (4) as follows

C2H5OH + 3H2O ⟶2CO2 + 6H2

ΔH0 = +1733 kJmol(2)

C2H5OH + 15O2 ⟶ 2CO2 + 3H2

ΔH0 = minus5520 kJmol(3)

C2H5O + 119909119909O2 + (3 minus 2119909119909)H2O ⟶2CO2 + (6 minus 2119909119909)H2

ΔH0 = 1733 minus 119909119909lowast552 kJmol

(4)

e SR of ethanol reaction (2) is an endothermicreaction which takes place at temperatures between 673 and1073K and with a kinetic slower than the PO reactionSR operates at lower temperature and produces a highernumber ofmolecules ofH2 permolecule of converted ethanol(H2C2H5OH = 6) thus the overall efficiency of this reactionis higher than that obtained by PO processes

e PO of ethanol reaction (3) occurs between 973 and1273K It is an exothermic reaction It has several advantagesallows working with adiabatic reactors without the necessityto supply external heat and the kinetics is rapid Obtaininghydrogen from bioethanol by reaction PO is an option thathas been rarely investigated because it would involve theseparation of water included in raw bioethanol which wouldmean a high energy cost

e third option combines the advantages of bothapproaches SR and PO is option includes the simultane-ous reaction of ethanol with water vapor and oxygen in anoxidative reforming process (autothermal reforming ATR)reaction (4) e input of the external heat is not necessarysince it is generated by introducing small amounts of oxygenemoles of H2 obtained permole of ethanol are higher thanthat in the case of the PO reaction but lower than that in thecase of SR

e choice of the reforming route is based on the typeof fuel cell the demands and volume of the system andmanagement strategy Nevertheless the SR of ethanol hasbeen the most studied route e amount of publishedstudies on the SR of ethanol is lower than that onhydrocarbons or methanol Several reviews about thedevelopment of catalysts applied to ethanol SR havebeen published lately [67ndash70] Catalytic materials such as


ITQ-2 Hexagonalprism

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

Co or Ni particles

12 MR

10 MR

F 3 Structure of delaminated zeolite ITQ-2 [103]

metallic oxides (ZnO MgO V2O5 Al2O3 TiO2 La2O3CeO2 SmO3) [71ndash73] supported metals (Co Al2O3CoLa2O3 CoSiO2 CoMgO CoZrO2 CondashZnO CoTiO2 CoV2O5 CoCeO2 CoSm2O3 CoCeO2ndashZrO2Co C NiLa2O3 Ni(La2O3ndashAl2O3) NiAl2O3 NiMgONindashCuSiO2 NindashCuAl2O3 NindashCundashKAl2O3) [74ndash85] andprecious metals supported on oxides (RhTiO2 RhSiO2RhCeO2 RhZrO2 RhAl2O3 RhMgO RhAl2O3RhCeO2ndashZrO2 RhndashAuCeO2 RhndashPtCeO2 PdCeO2PtCeO2 AuCeO2 PdAl2O3 PtndashPdCeO2) [86ndash99] arereported in these reviews

ermodynamic analyses have shown that a high con-version of ethanol to hydrogen is possible above 523K andalso that the highwaterethanolmolar ratio of raw bioethanolis benecial to increase hydrogen yield and to decrease theformation of byproducts such as methane carbonmonoxideand carbon deposition Table 1 shows a summary of thepossible reaction pathways followed by the ethanol during itscatalytic SRe extension in which each reaction takes placeover the catalyst will depend on the nature of metal type ofprecursor preparation method type of support presence ofadditives and operating conditions

Among them it is found that support plays an importantrole in the preparation of highly active and selective ethanolsteam reforming catalysts since it helps in the dispersion ofmetal catalyst and enhances its activity via metal-supportinteractions Specically it has been found that high surfaceareas of the support improve the catalytic activity [73 100]and the particular topology or crystalline structure of onesupport can affect the metal dispersion of the metallic parti-cles improving their stability against sinterization [101 102]Taking this into account the singular structure of zeoliteswould make these materials attractive to be used as supportsfor dispersing active metal phases [102ndash105]

Campos-Skrobot et al [103] reported the rst work inthe steam reforming of ethanol using zeolites as supportSpecically they studied the Y-zeolite exchanged with NaAccording to the results reported by these authors the NaYzeolite had the prime function of increasing the surface areaaiming higher reforming reaction efficiency Potassium andrhodium were added to NaY zeolite in order to improvereforming performance ey found that the addition ofRh and K allowed to prepare an ethanol steam reformingcatalyst with high activity and H2 selectivity Best conversion

Swollen

material

Calcined

NU6(2)

NU6(1)

Sonication

ITQ-18

Calcined Co0

CTMA+

F 4 Synthesis of delaminated zeolite ITQ-18 (adapted from[105])

valueswere achieved for higherH2Oethanol ratio and higherreagent ow ey also veried that reagent ow has greaterinuence on hydrogen yield than K additioney concludedthat NaY zeolite-supported Rh can be considered promisingcatalyst for ethanol steam reforming when compared withother existing studies

Chica et al [102 105] also studied zeolitic materials assupport of catalyst for the SR of bioethanol ey used twodelaminated zeolites (ITQ-2 and ITQ-18) with high externalsurface area (835 and 611m2g resp) to support Ni and Co

ITQ-2 delaminated zeolite consists of thin sheets of25 nm in height presenting a hexagonal array of ldquocupsrdquo(07 nm times 07 nm) that penetrate into the sheet from bothsides connected by a double 6-member ring (MR) window(Figure 3) [102] ITQ-18 is another delaminated zeolite whichhas been obtained by expanding and exfoliating a laminarprecursor of NU-6 zeolite [106] (Figure 4) e singularstructure of these delaminated zeolites and particularly thevery high and well-dened external surface area makes thesematerials very attractive to be used as supports for dispersingactive metal phases

Ni and Co were supported on pure silica ITQ-2 andCo on ITQ-18 with low aluminum content (SiAl = 100)For comparison reasons catalysts based on amorphous silicacontaining the same amount of Co and Ni (20wt) werealso prepared High catalytic activity selectivity and stability(again coke deposition) were reported for the delaminatedzeolite-based catalysts e excellent catalytic performanceexhibited was attributed to the combination of three effectsIt was attributed rst to the absence or very low concen-trations of acid sites in the delaminated ITQ-2 and ITQ-18 zeolites respectively e absence of acid sites wouldhelp to decrease the dehydration reaction that leads to theformation of ethylene and subsequent formation of coke themain causative of the catalyst deactivation It was attributedsecond to its high external surface which can provide alarge surface for coke deposition and help to slow downthe deactivation effects and third to the especial structure


of these delaminated zeolites formed by array of ldquocupsrdquodistributed along of sheets (see Figures 3 and 4) whichcan provide an excellent position for the stabilization of theNi and Co metal particles improving their dispersion andpreventing their agglomeration during the reduction andreaction stages An important conclusion was that while anamorphous support such as SiO2 leads to Co and Ni-basedcatalysts with low stability the use of delaminated zeoliteswith a crystalline structure allowed to prepare a much morestable bioethanol steam reforming catalyst

In the before reported studies zeolites are acting as simplesupports for metals for ethanol steam reforming [102ndash105]However since zeolites exhibit functional properties such asion exchange the charge state of the metal could affect theSR of ethanol In this line Inokawa et al [104] comparedthe ethanol reforming properties of zeolite Y supportingtransition metals and encapsulating transition metal cations

ey studied the catalytic activity of conventional zeoliteY with a SiAl ratio of 275 loaded with Ni and Co andtheir cations e results obtained suggest that transitionmetals selectively enhanced the dehydrogenation of ethanolIn addition the incorporated transition metal cations byion exchange led to the production of mainly C2H4 duringethanol steam reforming indicating that the presence ofthe cations accelerates the dehydration of ethanol usthe presence of transition metal cations in zeolite Y seemsto have a signicant inuence on the ethanol reformingreaction ese authors suggest that conventional zeolitessupporting transitionmetals aremore attractive for industrialapplications than zeolites with a high SiAl ratio supportingnoble metals due to advantages of cost and availabilityalthough the H2 yields produced by Y zeolite containing Coand Ni cations were inferior to that for zeolite Y supportingRh [103] In addition they think that H2 production fromethanol using zeolites with low or medium SiAl ratiossupporting transition metals such as Co and Ni could beimproved by the removal of the metal cations within thezeolites

One important factor affecting the stability of steamreforming catalysts is the formation of carbonaceousdeposits ese deposits can block the active sites andnally encapsulate the metallic particles deactivating thecatalyst completely erefore the stability of the catalysts isdirectly related to their tendency to form carbon e cokeformation on the catalysts during reforming of ethanol is dueto the imbalance between their formation and consumptionreactions (Table 2) is balance formationconsumption isdetermined by the reaction conditions and especially by theselected catalyst composition active phase and support

In order to reduce the coke formation over zeolite-based catalysts and increase the ethanol SR activity atlow temperature Kwak et al [107] prepared MgOzeoliteY catalysts loaded with bimetallic Ni-Ga e impregna-tion of Ga between the Ni and Mg components led tosignicantly higher reforming activity compared to theconventional NiMgzeolite Y catalyst e main productsfrom steam reforming over the NiGaMgzeolite Y catalystwere only H2 and CH4 at above 550∘C and the cata-lytic performances depended on the amount of Ga H2

production and ethanol conversion were maximized overNi(10)Ga(30)Mg(30)zeolite Y at 973K ethanol H2O =1 3 and a gas hourly space velocity (GHSV) of 6740 hminus1ishigh performance was maintained for up to 59 h

ese authors also studied the deactivation of thesecatalysts ey found that deactivation was largely retardedin the zeolite-based catalyst containing Ga compared to thatof the catalyst withoutGae authors reported that aer 60 hthe XRD peaks of the carbon and Ni metal were too enlargedwhile the other peaks assigned to metal or metal oxidesspecies were very small (Figure 5) e improved stabilityat the slower deactivation rate achieved with the NiGasample could not be unequivocally attributed to carbonformation e simultaneous addition of NiGa could alsohave depressed the sintering between the Ni and the supportcontributing to retard of the catalytic deactivation

It is clear that basicity decreases signicantly the for-mation of coke since it contributes to the inhibition ofside reactions that would lead to the formation of cokeprecursors (Table 2) In this sense Inokawa et al [108]studied the ethanol steam reforming over Ni supported onzeolite Y with basicity controlled by the exchange of alkalications As a result it was found that the exchange ofNa+ for K+ and Cs+ affected not only characteristics of thezeolites such as adsorption and basicity but also those ofNi such as reducibility and catalytic activity Ion exchangemainly brought an increase of basic sites which were slightlystrengthened It was found that Ni species on the Cs-Y zeolitewere reduced at a lower temperature than Na-Y zeolite H2production at 573K was improved in the order of NiNa-Y lt NiK-Y lt NiCs-Y according to the size of the cationin the zeolite and the amount of basic sites Improvement ofthe catalytic performance was considered to be due to theincrease of basic sites which weaken the OH bond of ethanoladsorbed on the zeolite In terms of elementary reactions thedehydrogenation reaction of ethanol was accelerated by thebasicity of the zeolite whereas the dehydration reaction thatproduces ethylene was inhibited

e basicity of the zeolite was found to be effective forthe inhibition of coke deposition because NiCs-Y withhigher H2 production than NiNa-Y also exhibited higherresistance to carbon deposition In summary an increase ofthe zeolite basicity by cation exchange can selectively promotethe dehydrogenation of ethanol by Ni on the zeolite andimprove H2 production and resistance to carbon deposition

Ni and Co have been the active sites more studied inthe SR of ethanol using zeolites as support Neverthelessother metals as Sn have been also found actives Lee et al[109] studied the production of hydrogen using Y zeolitepromoted with Sn and K ey studied the effects of the Snand K presence on the H2 production and on the catalyticdeactivation ey reported that the Sn component playedan important role in the oxidation of the feed gases duringethanol reforming while the addition of the K depressedthe formation of CH4 or others hydrocarbon intermediatesBased on the results of H2-TPR and NH3-TPD they suggestthat the reduction of Sn oxides (Sn4+ to Sn0) on SnO2-K2OY catalyst at low temperatures easily occurs compared


T 2 Reaction network for the steam reforming of bioethanol

Reaction EquationReforming with excess of water CH3CH2OH + 3H2O⟶ 2CO2 + 6H2

Reforming with decit of water CH3CH2OH + H2O⟶ 2CO + 4H2

CH3CH2OH + 2H2 ⟶ 2CH4 + H2O

Dehydrogenation CH3CH2OH⟶ C2H4O + H2

Acetaldehyde decomposition C2H4O⟶ CH4 + COAcetaldehyde reforming C2H4O + H2O⟶ 3H2 + 2CO

Dehydration CH3CH2OH⟶ C2H4 + H2OCoke formation C2H4 ⟶ polymeric deposits (coke)

DecompositionCH3CH2OH⟶CO + CH4 + H2

2CH3CH2OH⟶ C3H6O + CO + 3H2

CH3CH2OH⟶ 05CO2 + 15 CH4

Methanation CO + 3H2 ⟶ CH4 + H2OCO2 + 4H2 ⟶ CH4 + 2H2O

Decomposition of methane CH4 ⟶ 2H2 + C

Boudouard reaction 2CO⟶ CO2 + C

Water gas shi reaction CO + H2O⟶ CO2 + H2

Zeolite Y

Ga2O3

Ni

Carbon

MgO

NiO

Inte

nsi

ty (

au

)

(h) NiGaMgzeolite Y(10 30 30) after reaction

(g) NiGaMgzeolite Y(10 30 30)

(f) NiGaMgzeolite Y(10 20 30) after reaction

(e) NiGaMgzeolite Y(10 20 30)

(d) NiGaMgzeolite Y(10 10 30) after reaction

(c) NiGaMgzeolite Y(10 10 30)

(b) NiMgzeolite Y(10 30) after reaction

(a) NiMgzeolite Y(10 30)

5 20 40 60 80 100

F 5 Comparison of XRD patterns of the catalysts Ni(10)Ga(x)Mg(30)zeolite Y (119909119909 119909 119909119909 119909119909119909 119909119909119909 119909119909119909 according to the reactiontemperature before and aer reaction [107]

to conventional Ni120574120574-Al119909O119909 catalysts In addition the acidityof theNi120574120574-Al119909O119909 catalyst induced by the existingAl is higherthan that presented in the SnO119909-K119909OY catalyst us thecondensation of ethanol on the last catalyst is more difficultand consequently the formation of the coke is lower andeventually the higher activity over SnO119909-K119909OZY catalyst ismaintained

Considering all the above mentioned it seems thatthe use of zeolites as metal support to prepare active and

stable reforming catalyst to produce hydrogen could be anattractive option since they have a high external surfacearea and can be prepared with neutral behaviors if theysynthesized all silica with high SiAl ratios or exchangedwithalkaline metals However pore opening of zeolites can limittheir application to the reforming of large molecules usmesoporous molecular sieves with size-tunable mesoporeshave attracted a great deal of attention because of theircontrollable structure and composition [110 111] However


unlike zeolites the wall of the mesoporous is amorphous notcrystalline erefore mesoporous aluminosilicates cannotexhibit the excellent catalytic properties unlike acidic zeolitesMoreover their hydrothermal stability is especially low Toovercome this problem one strategy has been the generationofmesoporosity on zeolites [112ndash114]e presence ofmeso-pores in the crystalline of the zeolite would be equivalent toincreasing the external surface of the zeolites making a largernumber of pore openings accessible to the large reactants[115ndash121] On the other hand the presence of mesoporouscould improve the diffusion affecting the ion exchangeprocesses and catalytic reaction [122ndash129] Although ethanolis a small molecule from biomass processing most part ofthe molecules from biomass susceptible to be reformed arelarge (ie glycerin sugars cellulose lignin hemicelluloseand so forth) making the mesopore-modied zeolites anattractive material to prepared hydrothermally stable steamreforming catalysts In this line da Costa Serra et al [130]studied the effect of mesopores-modied mordenite zeolitepromoted with Ni in the steam reforming of bioethanoleyreported the alkaline treatment of a commercial mordeniteto generate mesoporosity (Figure 6)e idea was to generatemesoporosity in the commercial mordenite zeolite in orderto improve the exchange of alkaline cation (to remove theacidity) and create good positions for the incorporationand stabilization of Ni metallic particles (active sites forsteam reforming of bioethanol) ey found that reformingactivity of catalyst based on mesopores-modied mordenitewas signicantly higher than that shown by the commercialone (without mesopores) e lower size of the Ni metal-lic particles supported on mesopores-modied mordenitewere the main factor responsible for this high activity H2selectivity and catalytic stability were also found higherfor the mesopore-modied material ey reported thatthe formation of coke precursors (favored by acid sites)and the subsequent deposition of carbon was lower in themesopore-modied mordenite is effect is explained bythe generated mesoporosity which would improve rst theNa exchange and thus the neutralization of the acid sitesand second the diffusion of the reactants and productsavoiding the blockage of micropores Indeed for the sameNa exchange conditions the amount of Na exchanged wasfoundhigher in themesopores-modiedmordenite (42 wtagainst 29 wt for original mordenite) suggesting thatthe presence of mesopores would improve the exchange ofprotons (responsible of acid sites) by sodium cations Onthe other hand they observed a higher enlargement of theNi metallic particles supported on not treated mordenite(without mesopores) suggesting that generated mesoporos-ity could be contributing to the generation of good positionfor the incorporation and stabilization of Ni metallic par-ticles avoiding or decreasing the Ni sinterization and thusimproving the catalytic activity and stability

All the works mentioned above have been centered in thereforming of ethanol or bioethanol in gas phaseNeverthelessin the literature the use of zeolites in the reforming of ethanolin liquid phase is also reported Aqueous phase reforming(APR) has been recently reported by Dumesic et al [131ndash133] is process operates at low temperatures (lt573K) at

which the WGS reaction is also thermodynamically favoredmaking it capable of producing hydrogen with high yieldse low reaction temperature minimizes the decompositionreactions and hence avoids carbonization and catalyst deac-tivation Tang et al [134] studied the feasibility of platinum-loaded NaY zeolite catalysts for APR of methanol andethanol e feasibility of APR of ethanol was demonstratedon the PtNaY catalysts e results were compared with thedata on Pt120574120574-Al2O3 catalysts At 538K the 05 wt PtNaYachieved higher H2 selectivity and lower alkane selectivitythan the 3wt Pt120574120574-Al2O3 catalyst with similarly highethanol conversion of sim97 on both catalysts e zeolite-based catalysts with the advantages of high activity reduceduse of precious metal and low cost of zeolite materialsdeserve further investigations ey report that research isongoing into the effect of substrate properties on the catalyticperformance of platinum catalysts in APR reactions

22 Zeolites as Constituents of Photocatalysts for theSustainable Production of Hydrogen via Water Splitting

221 Solar Energy and Water Splitting Reaction eincidence of solar energy on the surface of the earth(180000 TW) by far exceeds all human energy needs [135]us it is easy to understand that the solar energy couldbe considered one of the most important renewable energysources potentially available on earth

Undoubtedly solar energy is the largest renewablecarbon-free resource amongst all other renewable energyoptions However to make use this energy by the currentlyhuman technology solar energymust be captured convertedand stored in order to assure a continuous supply of energyand to overcome the diurnal cycle and the intermittency ofthe terrestrial solar resource

Among the different energy carriers capturing the solarenergy hydrogen from photocatalytic water splitting is con-sidered as one of the most promised carriers since it allowsstoring solar energy in the form of chemical energy andmakes available solar energy for 24 hours a day 7 days a week

In the photocatalytic water splitting hydrogen is pro-duced from water using sun light and specialized semicon-ductors e semiconductor uses light energy to directlydissociate water molecules into hydrogen and oxygen ewater splitting takes place when the semiconductor is irra-diated with light in the presence of an electron donor andacceptor oxidizing OHminus ions to produce O2 and reducingH+ ions to H2 Specically the electrons in the valenceband of the photocatalyst are excited to the conductionband while the holes are le in the valence band istherefore creates the negative-electron (eminus) and positive-hole (h+) pairs is stage is referred to the semiconductorrsquosldquophoto-excitedrdquo state and the energy difference between thevalence band and the conduction band is known as the ldquobandgaprdquo is must correspond to the wavelength of the lightfor it to be effectively absorbed by the photocatalyst Aerphotoexcitation the excited electrons and holes separateand migrate to the surface of the photocatalyst In thephotocatalytic water-splitting reaction they are used as a


MOR original

(a)

MOR modified

(b)

F 6 TEMmicrophotographs of original and alkaline treated mordenite to generate mesoporosity Adapted from [130]

reducing agent and oxidizing agent to produce H2 and O2respectively A schematic representation of the principle ofthe photocatalytic system for water is shown in Figure 7[136] As it can be seen rst that OndashH bonds of twowater molecules need to be broken with the simultaneousformation of one O=O double bond as follows [137]

H2O ⟷ O2 + 4eminus + 4H+

Eanodic = 123V minus 0059 10076491007649pH10076651007665 V (NHE) (5)

Since this reaction requires a high oxidizing potential123V versus NHE (normal hydrogen electrode) (pH = 0)the top level of valence band has to be more positive thanthis potential so that the photogenerated holes have enoughenergy to oxidize water is reaction releases four protons(H+) and four electrons (eminus) which need to be combined toform two H2 molecules as follows [136]

4H+ + 4eminus ⟷ 2H2

Ecathodic = 0V minus 0059 10076491007649pH10076651007665 V (NHE) (6)

erefore the conduction band of the semiconductor has tobe more negative than water reduction potential (0 V versusNHE (pH = 0)) us water molecules are oxidized by theholes to form O2 and are reduced by the electrons to formH2 for overall water splittingerefore the theoretical mini-mum band gap for water splitting is 123 eV that correspondsto light wavelength of about 1000 nm

222 Semiconductors and Zeolites for Water Splitting Cur-rently the photocatalytic water splitting over semiconductormaterials is an area of great interest due to the potential ofhydrogen as a clean-energy fuel source Since the initial worksof Fujishima and Honda [138] who discovered that watercan be photoelectrochemically decomposed into hydrogenand oxygen using a semiconductor (TiO2) electrode underUV irradiation an extensive variety of materials (TiO2 CdSZnO ZrO2 titanates niobates and tantalates) [139ndash151]have been reported to be effective for the photocatalyticdecomposition of water

Initial efforts in this area involved large bandgap (Eg gt30 eV) semiconductors that used only UV light Currently

CB

VB

H+

H2

minus

+

4H+

+ 4eminus rarr 2H2uarr

0 V

+123 V

eminus

h+

O2H2O

2H2O + 4h+

rarr O2uarr + 4H+

F 7 Schematic diagram of band edge requirements for watersplitting reaction Adapted from [137]

the most important efforts are being focused on using visiblelight as the energy source [152ndash170] as the ultimate goal toproduce hydrogen fuel using solar energy While the overallredox potential of the reaction

H2O + h120584120584120584 H2 +12O2 (7)

is only minus123 eV (1000 nm) at pH 7 the crucial reaction forhydrogen production is believed to be the initial one-electrontransfer to H+ ion

H+ + eaqminus 120584 Haq

bull (8)

where EH = minus25V at pH 7 which falls energetically withinthe visible region of light

Taking into account the basic mechanism and reactionsof photocatalytic water splitting process the photocatalystsshould meet several characteristics with respect to semicon-ducting and electrochemical properties [171ndash175] as follows(1) narrow band gap (123 eV lt Eg lt 30 eV) and bandedge potentials suitable for overall water splitting to be acti-vated under visible light (2) successive separation of photo-excited electrons from reactive holes (3) minimum energylosses associated with charge transport and recombination


of photo-excited charges (4) corrosion and photocorrosionresistivity in aqueous mediums (5) facilitated electron trans-fer properties fromphotocatalyst surface towater and (6) lowproduction cost

Tomeet part of the abovementioned expectations exten-sive studies have been performed based on the use of supportwhere effective photocatalysts have been impregnated [176ndash183] e major incentives for implementing the supportedphotocatalyst idea are (1) inhibition of the back electrontransfer as limiting parameter in redox systems (2) takingadvantage of nanosized semiconductors while using them ineasily separable microsized level of the support (3) utilizingthe support to add more solid chemical promoters and (4)structural and chemical characteristics of the support byitself

Among the different supports used to prepare effi-cient water splitting photocatalysts zeolites are presentedas promising materials Zeolites exhibit high surface areaunique nanoscaled porous structure and ion exchange prop-erties which can be used in the design of highly efficient pho-tocatalysts [184] Unique photocatalytic properties whichcannot be realized in normal catalytic systems have beenobserved recently in such modied spaces [185ndash190] It isimportant to note that zeolites can also provide specicphotophysical properties such as the control of charge trans-fer and electron transfer processes [191ndash194] which is veryimportant in photocatalytic reactions

ere are several advantages that zeolites afford as sup-port or host of semiconductor particles For example the poresizes of the host supportmaterial control the resulting particlesize of the supported semiconductor Particle size is a crucialfactor in the dynamics of electronhole recombination pro-cesses especially in semiconductor nanomaterials and thatthe movement of electrons and holes is primarily governedby the well-known quantum connement [195] Generally adecrease in particle size could be expected to lead to a higherefficiency in photocatalysis [196ndash201] is was because thebulk charge recombination of photogenerated electrons andholes dominant in the well-crystallized large semiconductorparticles was reduced by decreasing particle size Reductionin particle size could also lead to a larger surface area and anincreased available surface active sites [202ndash204]

ecreasing particle size has a known benecial effecton catalyst efficiency [205ndash208] Furthermore encapsulationinto a porous structure should provide some protectionagainst surface-mediated reactions that corrode the catalystas exposed surface area will be limited In addition a majorfactor that limits the efficiency of the most part of thephotocatalysts is electron-hole recombination

e incorporation of photocatalysts into the microporestructure of zeolite in order to prepare nanoparticles is anattempt to improve their photocatalytic activity and photo-stability Small nanoparticles show a higher photocatalyticactivity compared to the bulk materials due to changes inthe surface area band gap morphology and generation ofsurface defects [209 210] In addition the incorporation ofphotocatalyst into solid matrices as zeolites is reported tosuppress photocorrosion and improve the activity for waterreduction e incorporated nanoparticles whose sizes are

determined by the nanometric size of zeolite cages showsome novel physical properties such as blue shi of opticalabsorption spectra increased photooxidation potentials andthird-order nonlinear optical properties In this line Sathishet al [211] reported the preparation of cadmium sulphide(CdS) nanoparticles by precipitation process using differentzeolite matrices as templates (H-Y HZSM5 and H-120573120573) Inthis study the micropores of zeolites were used as molds toprepare nanoparticles of CdS with different sizes Aer theremoval of zeolite phase the CdS nanoparticles were used ascatalysts for the photocatalytic decomposition of water ehydrogen evolution ratewas foundhigher than that presentedby the bulk samples which correlated quite well with theparticle size and surface area

Of particular interest is the use of zeolites as supportbecause of the well-dened microporous structure and ion-exchange properties as was mentioned before One of therst work reported in the literature about the use of zeolitesas support to produce hydrogen by water splitting processwas carried out by Fox and Pettit [209] ey studied thephotocatalytic hydrogen evolution on zeolite-supported CdSparticles modied by surface modication with an appropri-ate hydrogen evolution catalyst (Pt or ZnS) Particles formedwithin the zeolite cavities aggregate upon exposure to waterand small clusters were isolated within individual cavitiesonly in nonaqueous solvents at low CdS loading levels (lt3)Sustained hydrogen evolution required the presence of anadded sacricial donor (S2minusSO3

2minus) Platinum deposited onthe photoactive CdS surface is exclusively found inside thecavity where it was inaccessible to large anionic reagents

Ryu et al [212] also studied the water splitting activity ofCdS particles supported on several micro- and mesoporoussilicas (zeolites Y and L mesoporous SBA-15) Specicallythey studied the hydrogen production from waterethanolsolutions using visible light All catalysts were active inthe photocalytic water splitting with the following orderof photoreactivity zeolite-Y gt SBA-15 gt zeolite-L eyfound that optimization of reaction conditions (ie pH ionicstrength and water-to-alcohol ratios) was critical to achievea high level of hydrogen production Preventing loss of CdSduring the course of the photoreaction is also paramount tocreate a stable long-term use catalyst Specically they foundthat there was an efficient dispersion of CdS nanoclusters intothe cages and micropores of zeolite Y and the quantum con-nement of hydrated CdS increased the reduction potentialfor the bound proton to hydrogen atom electron transferand nally the conned CdS supercluster in a more efficientchromophore in the visible portion of the spectrum

e water splitting activity with visible light usingCdS nanocomposites (quantum-sized (Q-sized) CdSCdS nanoparticles embedded in zeolite cavities (CdSzeolite) and CdS quantum dots (Q-CdS) deposited onKNbO3 (CdSKNbO3 and NiNiOKNbO3CdS)) wasalso investigated by Ryu et al [213] ey reported thatthe rate of H2 production in alcoholwater mixtures andother electron donors at 120582120582 120582 400 nm was clearly higherin the the hybrid catalysts including zeolite-basedphotocatalyst e relative order of reactivity as a function


of catalyst is Ni(0)NiOKNbO3CdS gtNi(0)KNbO3CdS gtKNbO3CdS gt CdSNaY-zeolite gt CdSTiY-zeolite gt CdSwhile the reactivity order with respect to the array of electrondonors is 2-propanol gt ethanol gtmethanol gt sulte gt sulde

Titanium exchanged zeolites have been also studied in thewater splitting reaction Yue and Khan [214] were one of therst reporting the use of titano-zeolites to produce hydrogenby water splitting In their study the Ti was exchanged andincorporated into the framework of zeolite A Specicallythey studied the effect of several variables on the photoas-sisted production of hydrogen over this titanium-exchangedzeolite During the reaction oxygen tended to react withtitanium ions exchanged on zeolite forming titanium oxidesultimately leaving the zeolite surface thereby creating vacantsites ese vacant sites were occupied by hydrogen aerthe absorbed hydrogen was successfully displaced from thezeolite structure by the addition of base

Zeolites containing titanium in their framework havebeen also used as support of CdS nanoparticles In this lineGuan et al [215 216] studied the water splitting activity ofCdS encapsulated on ETS-4 and ETS-10 titanosilicalite zeo-lite ey found a stable photocatalytic activity under visiblelight irradiation (120582120582 gt 420 nm) in aqueous solution containingNa2S and Na2SO3 as electron donors Specically the cat-alytic activity for the zeolite-based photocatalysts was foundhigher than that for CdS bulk (175 and 133 120583120583mol H2hgcatalyst forCdSETS-4 andCdSETS-10 resp and 83120583120583molH2hg catalyst for CdS bulk) ese results seem to indicatethat the encapsulation of CdS in these titanosilicalite zeolitesis effective for separating charge-carries photogenerated inCdS and for improving the activity as well as the stability

Dubey et al [217] reported the use of zeolite Y to preparehighly efficient water splitting catalysts under visible lightey reported the incorporation in the zeolite Y of tita-nium dioxide (TiO2) heteropolyacid (HPA) and transitionmetals like cobalt (Co) ey got a photocatalyst where theTiO2 was effectively dispersed and stabilized on the zeolitesurface e high efficiency of the composite photocatalystwas explained by the synergetic work of TiO2 with Co andheteropolyacidwhichmade thematerial active in visible lightfor photoreduction of water to hydrogen ey also reportedthat the aluminosilicate framework of zeolite also contributedtowards delayed charge separation

In the previous studies zeolites have been used for theseparated incorporation of nanoparticles of CdS and titanium(as titanium oxide particles (TiO2) or Ti3+ taking part ofthe zeolite framework) In this way improved water splittingcatalysts were obtained Recently works carried out byWhiteet al [218] report the incorporation of both semiconductorsin zeolite Y ey observed improvements in H2 evolutionrates of sim300 for CdSTiO2 zeolite Y over TiO2 zeolite Yand sim18 for CdSTiO2 zeolite Y over CdS zeolite Y eseimprovements exceed colloidal binary systems reported inthe literature On the other hand improvements in the H2evolution rate of the ternary system PtCdSTiO2-zeoliteY was not as marked as compared to the best colloidalternary systems reported in the literature ey proposedan interesting model to explain the colocalization of the

TiO2 and CdS nanoparticles supported on zeolite Y ismodel explains quite well the high activity of binary system(CdSTiO2 zeolite Y) and also why the incorporation of Ptdid not improve the catalytic activity of the ternary system(PtCdSYiO2 zeolite Y)emain reasonwas that Pt neededto be associated only with TiO2 for best H2 evolution andthe zeolite promoted self-assembly did not provide a route forpositioning the Pt only on the TiO2 particles New strategiesfor the incorporation of Pt will be required in order topromote the association of Pt only with TiO2

3 Conclusions

e intense exploitation of fossil fuels to satisfy the globallygrowing energy demand has caused an increase of CO2 inthe atmosphere and therefore a signicant global warming(green-house effect) Furthermore the reserves of fossil fuelson earth are nite and no matter how long they will lasta cleaned and renewable energy alternative independent offossil fuels has to be developed for the future Hydrogencould be a good option because it exhibits the greatest heatingvalue (394 kWhkg) of all chemical fuels Its combustionto heat or power is simple and clean When combustedwith oxygen hydrogen forms water and no pollutants aregenerated or emitted About 95 of the hydrogen we usetoday comes from reformingnatural gas But to realize the fullbenets of a hydrogen economy increased energy securitydiverse energy supply and reduced air pollution hydrogenmust be produced cleanly efficiently and affordably fromavailable renewable resourcesus renewables are a desiredenergy source for hydrogen production However there aremany challenges to produce hydrogen from renewables andprobably the major one is developing new catalytic processto produce sustainable hydrogen and reducing the cost to becompetitive with the current fuels (gasoline and diesel)

Zeolites are presented as excellent catalysts and support ofcatalysts due to their very special physicchemical properties

(i) High surface area(ii) Molecular dimensions of the pores(iii) High adsorption capacity(iv) Partitioning of reactantproducts(v) Possibility of modulating the electronic properties of

the active sites(vi) Possibility for preactivating the molecules when in


Currently new scientic applications have been devel-oped for these materials Among them the production ofgreen fuels from renewable sources is the focus of a large partof the research efforts

Two different routes to produce sustainable hydrogenusing zeolites have been described and revised in this paperOne of them is based on the biomass conversion via indirectthermochemical conversion to intermediate products eindirect thermochemical option is related to the conversion


of biomass to biofuels (bioethanol biodiesel biogas) fol-lowed by catalytic steam reforming of them to hydrogenAn advantage of this approach is that the biofuels as anintermediate product have a higher energy density thanthe biomass feedstock and can be transported more easilySpecically this paper has considered the steam reformingof bioethanol

Renewable bioethanol is an interesting hydrogen sourcethrough steam reforming but its CndashC bond promotes parallelreactions mainly coke and by-products formation In thisway good ethanol reforming catalysts are still needed euse of zeolites has been able to improve the catalytic activityselectivity and stability of the bioethanol steam reformingcatalysts It has been reported that zeolites play an importantrole in the preparation of highly active and selective ethanolsteam reforming catalysts since they help in the dispersion ofmetal active sites and enhance their activity viametal-supportinteractions Specically it has been found that high surfaceareas of the support improve the catalytic activity and that theparticular topology or crystalline structure of one support canaffect themetal dispersion of themetallic particles improvingtheir stability against sinterization

Another interesting option analyzed in this paper withenormous potential but requiring more development timehas been the photocatalytic decomposition of water usingsolar energy which is also called water splitting In thephotolysis of water solar photons area is used to producehydrogen directly via electrochemical systems is methodinvolves the dissociation of water into hydrogen and oxygendirectly at the surface of a semiconductor through theirradiation of the semiconductor by solar photons ephotovoltaic semiconductor material acts as a catalyst toproduce hydrogen directly at the semiconductor and waterinterface

It has been shown that among the different supports usedto prepare efficient water splitting photocatalysts zeolitesare presented as promising materials Zeolites exhibit highsurface area unique nanoscaled porous structure and ionexchange properties which can be used in the design ofhighly efficient photocatalyst In addition zeolites can alsoprovide specic photophysical properties such as the controlof charge transfer and electron transfer processes which arevery important in photocatalytic reactions

It has been seen that there are several advantages thatzeolites afford as support or host of semiconductor particlesFor example the pore sizes of the host support materialcontrol of the resulting particle size of the supported semi-conductor Semiconductors such as TiO2 and CdS have beenincorporated in zeolites in order to improve their photocat-alytic activity and photostability Small nanoparticles of thesesemiconductors incorporated in zeolites have been reportedto show a higher photocatalytic activity compared to thebulk materials due to changes in the surface area band gapmorphology and generation of surface defects In additionthe incorporation of photocatalyst into zeolites helps tosuppress photocorrosion and improve the activity for waterreduction Although the studies presented here using zeolitescan be considered promising the major problem to solvewould be to nd a semiconductor material that had the right

photoelectrochemical properties while being economicaland robust enough to withstand the severe chemical andphysical environment

References

[1] A F Cronstedt ldquoRoumln och beskrifning om en obekant baumlrg artsom kallas Zeolitesrdquo Akademeins Handlingar Stockholm vol18 p 120 1756

[2] R M Barrer and D A Ibbison ldquoOcclusion of hydrocarbons bychabazite and analciterdquo Transactions of the Faraday Society vol40 pp 195ndash206 1944

[3] R M Barrer ldquoProcess for the manufacture of crystallineabsorbentsrdquo US Patent 2413134 1946

[4] R M Barrer ldquoSeparation of mixtures using zeolites as molecu-lar sieves I ree classes of molecular-sieve zeoliterdquo Journal ofthe Society of Chemical Industry vol 64 p 130 1945

[5] DW Breck ldquoCrystalline molecular sievesrdquo Journal of ChemicalEducation vol 41 no 12 pp 678ndash689 1964

[6] R M Milton ldquoPerformed zeolites and silicatesrdquo in MolecularSieves p 199 Society of Chemical Industry London UK 1968

[7] J A Rabo ldquoUnifying principles in zeolite chemistry andcatalysisrdquo Catalysis Reviews Science and Engineering vol 23no 1-2 pp 293ndash313 1981

[8] E M Flanigen ldquoZeolites and molecular sieves An historicalperspectiverdquo in Introduction To Zeolite Science and PracticeH van Bekkum E M Flanigen and J C Jander EdsStudies in Surface Science and Catalysis pp 11ndash37 ElsevierAmsterdam e Netherlands 2nd Completely Revised andExpanded Edition edition 1991

[9] E Houdry W F Burt A E Pew andW A Peters ldquoe houdryprocessrdquo Oil and Gas Journal Engineering and Operating Sec-tion vol 37 pp 40ndash45 1938

[10] httpwwwiza-onlineorg[11] J M Newsman ldquoe zeolite cage structurerdquo Science vol 231

no 4742 pp 1093ndash1099 1986[12] W M Meier and D H Olson Atlas of Zeolite Structure Types

Structure Commission of the International Zeolite Asociation1978

[13] C C Freyhardt M Tsapatsis R F Lobo K J Balkus Jr andME Davis ldquoA high-silica zeolite with a 14-tetrahedral-atom poreopeningrdquo Nature vol 381 pp 295ndash298 1996

[14] R F LoboM Tsapatsis C C Freyhardt et al ldquoCharacterizationof the extra-large-pore zeolite UTD-1rdquo Journal of the AmericanChemical Society vol 119 no 36 pp 8474ndash8484 1997

[15] T Wessels C Baerlocher L B McCusker and E J CreyghtonldquoAn ordered form of the extra-large-pore zeolite UTD-1 synthesis and structure analysis from powder diffractiondatardquo Journal of the American Chemical Society vol 121 no 26pp 6242ndash6247 1999

[16] PWagnerM YoshikawaM Lovallo K TsujiM Taspatsis andM E Davis ldquoCIT-5 a high-silica zeolite with 14-ring poresrdquoChemical Communications no 22 pp 2179ndash2180 1997

[17] A Burton S Elomari C Y Chen et al ldquoSSZ-53 and SSZ-59two novel extra-large pore zeolitesrdquo Chemistry vol 9 no 23pp 5737ndash5748 2003

[18] K Strohmaier and D E W aughan ldquoStructure of the rstsilicate molecular sieve with 18-ring pore openings ECR-34rdquoJournal of the American Chemical Society vol 125 no 51 pp16035ndash16039 2003


[19] A Corma M J Diaz-Cabantildeas J L Jorda C Martinez and MMoliner ldquoHigh-throughput synthesis and catalytic properties ofa molecular sieve with 18- and 10-member ringsrdquo Nature vol443 pp 842ndash845 2006

[20] J L Sun C Bonneau A Cantin et al ldquoe ITQ-37mesoporouschiral zeoliterdquo Nature vol 458 no 7242 pp 1154ndash1157 2009

[21] M E Davis C Saldarriaga C Montes J Garces and CCrowdert ldquoA molecular sieve with eighteen-membered ringsrdquoNature vol 331 no 6158 pp 698ndash699 1988

[22] S M Csicsery ldquoshape-selective catalysis in zeolitesrdquo in ZeoliteChemistry and Catalysis vol 171 p 680 1976

[23] S M Csicsery ldquoShape-selective catalysis in zeolitesrdquo Zeolitesvol 4 no 3 pp 202ndash213 1984

[24] E G Derouane ldquoNew aspects of molecular shape-selectivitycatalysis by zeolite ZSM-5rdquo Studies in Surface Science andCatalysis vol 5 pp 5ndash18 1980

[25] G E Derouane Zeolite Science and the Technology vol 80of NATO ASI Series E Martinus Nijhoff e Hague eNetherlands 1984

[26] A Corma ldquoInorganic solid acids and their use in acid-catalyzedhydrocarbon reactionsrdquo Chemical Reviews vol 95 no 3 pp559ndash614 1995

[27] A Corma and AMartinez ldquoZeolites and Zeotypes as catalystsrdquoAdvanced Materials vol 7 pp 137ndash144 1995

[28] J Weitkamp and S Ernst ldquoLarge pore molecular sieves chapter5 catalytic test reactions for probing the pore width of large andsuper-large pore molecular sievesrdquo Catalysis Today vol 19 no1 pp 107ndash149 1994

[29] W W Kaeding C Chu L B Young B Weinstein and SA Butter ldquoSelective alkylation of toluene with methanol toproduce para-Xylenerdquo Journal of Catalysis vol 67 no 1 pp159ndash174 1981

[30] R A Anderson ldquoMolecular Sieve Adsorbent Applications Stateof the Artrdquo in Molecular Sieves-II vol 40 of ACS SymposiumSeries chapter 53 pp 637ndash649 1977

[31] E M Flanigen ldquoMolecular sieve zeolite technology the rsttwenty-ve yearsrdquo in Proceedings of the Properties and Applica-tions of Zeolites p 760 Naples Italy 1980

[32] D B Broughton ldquoBulk separations via adsorptionsrdquo ChemicalEngineering Progress vol 73 p 49 1977

[33] H Odawara Y Noguchi and M Ohno ldquoFructose is effectivelyseparated from a mixture of sugars by contacting an aqueoussolution of a mixture of sugars with crystalline alumino-silicaterdquo US Patent 4014711 1977

[34] R W Neuziland and J W Preighitz US Patent 4024331 1977[35] H Minato and T Tamura Natural Zeolites Ocurrence Proper-

ties and Use Pergamon London UK 1978[36] J Novaacutekovaacute and Z Dolejšek ldquoA comment on the oxidation of

coke deposited on zeolitesrdquo Zeolites vol 10 no 3 pp 189ndash1921990

[37] A P Antunes M F Ribeiro J M Silva F R Ribeiro PMagnoux and M Guisnet ldquoCatalytic oxidation of tolueneover CuNaHY zeolites coke formation and removalrdquo AppliedCatalysis B vol 33 no 2 pp 149ndash164 2001

[38] A P Bolton Experimental Methods in Catalytic Research vol 2Academic Press New York NY USA 1976

[39] E M Flanigen ldquoZeolites science and technologyrdquo in Proceed-ings of the NATO ASI F R Ribeiro Ed p 4 Atinus Nijhoff1984

[40] H W Haynes ldquoChemical physical and catalytic properties oflarge pore acidic zeolitesrdquo Catalysis Reviews vol 17 no 2 pp273ndash336 1978

[41] E M Flanigen R W Broach and S T Wilson IntroducitonZeolites in Industrial Separation and Catalysis Wiley-VCHWeinheim Germany 2010

[42] H Beyer and I Belenykaja Catalyisis by the Zeolites Edited byY Imelik Elsevier Amsterdam e Netherlands 1987

[43] J Scherzer and J L Bass ldquoInfrared spectra of ultrastable zeolitesderived from type Y zeolitesrdquo Journal of Catalysis vol 28 no 1pp 101ndash115 1973

[44] N Y Chen ldquoHydrophobic properties of zeolitesrdquoe Journal ofPhysical Chemistry vol 80 no 1 pp 60ndash64 1976

[45] EM Flanigen JM Bennett RWGrose et al ldquoSilicalite a newhydrophobic crystalline silicamolecular sieverdquoNature vol 271no 5645 pp 512ndash516 1978

[46] E M Flanigen and R L Patton ldquoSilica polymorph and processfor preparing samerdquo US Patent 4073865 1978

[47] D W Breck Zeolite Molecular Sieves Structure Chemistry andUse John Wiley amp Sons New York NY USA 1974

[48] R M Barret Zeolites and Clay Minerals As Sorbents andMolecular Sieves Academic Press London UK 1978

[49] D W Breck Zeolite Molecular Sieves Wiley New York NYUSA 1974

[50] J Scherzer J L Bass and F G Hunter ldquoStructural char-acterization of hydrothermally treated lanthanum Y zeolitesI Framework vibrational spectra and crystal structurerdquo eJournal of Physical Chemistry vol 79 no 12 pp 1194ndash11991975

[51] P B Venuto L A Hamilton and P S Landis ldquoOrganic reac-tions catalyzed by crystalline aluminosilicates II Alkylationreactions mechanistic and aging considerationsrdquo Journal ofCatalysis vol 5 no 3 pp 484ndash493 1996

[52] J W Ward ldquoSpectroscopic study of the surface of zeolite YII Infrared spectra of structural hydroxyl groups and adsorbedwater on alkali alkaline earth and rare earth ion-exchangedzeolitesrdquo e Journal of Physical Chemistry vol 72 no 12 pp4211ndash4223 1968


[54] G A Ozin A Kuperman and A Stein ldquoAdvanced zeolitematerials sciencerdquo Angewandte Chemie vol 28 no 3 pp359ndash376 1989

[55] Z Wang A Mitra H Wang L Huang and Y Yan ldquoPure-silicazeolite low-k dielectric thin lmsrdquo Advanced Materials vol 13no 10 pp 746ndash749 2001

[56] EuropeanCommunities Office forOfficial Publications Hydro-gen and electricity New carriers and novel technologies for afuture clean and sustainable energy economy EU Brochure forthe Sixth Framework Programme KI-46-02-533-EN-D 2002

[57] MA Pentildea J P Gomez andG J L Fierro ldquoNew catalytic routesfor syngas and hydrogen productionrdquo Applied Catalysis A vol144 no 1-2 pp 7ndash57 1996

[58] J A Armor ldquoe multiple roles for catalysis in the productionof H2rdquo Applied Catalysis A vol 176 no 2 pp 159ndash176 1998

[59] D L Trimm and Z I Onsan ldquoOnboard fuel conversion forhydrogen-fuel-cell-driven vehiclesrdquo Catalysis Reviews Scienceand Engineering vol 43 no 1-2 pp 31ndash84 2001


[60] R M Navarro M A Pentildea and J L G Fierro ldquoHydrogenproduction reactions from carbon feedstocks fossil fuels andbiomassrdquo Chemical Reviews vol 107 no 10 pp 3952ndash39912007

[61] T A Milne C C Elam and R J Evans ldquoHydrogen frombiomassrdquo Report for the International Energy Agency IEAH2TR-02001 2002

[62] P C Hallenbeck and J R Benemann ldquoBiological hydrogen pro-duction Fundamentals and limiting processesrdquo InternationalJournal of Hydrogen Energy vol 27 no 11-12 pp 1185ndash11932002

[63] D Gardner ldquoHydrogen production from renewablesrdquo Renew-able Energy Focus vol 9 no 7 pp 34ndash37 2009

[64] G A Deluga J R Salge L D Schmidt and X E VerykiosldquoRenewable hydrogen from ethanol by autothermal reformingrdquoScience vol 303 no 5660 pp 993ndash997 2004

[65] J R Salge B J Dreyer P J Dauenhauer and L D SchmidtldquoRenewable hydrogen from nonvolatile fuels by reactive ashvolatilizationrdquo Science vol 314 no 5800 pp 801ndash804 2006

[66] R M Navarro M C Saacutenchez-Saacutenchez M C Alvarez-GalvanF D Valle and J L G Fierro ldquoHydrogen production fromrenewable sources biomass and photocatalytic opportunitiesrdquoEnergy and Environmental Science vol 2 no 1 pp 35ndash54 2009

[67] P D Vaidya and A E Rodrigues ldquoInsight into steam reformingof ethanol to produce hydrogen for fuel cellsrdquo Chemical Engi-neering Journal vol 117 no 1 pp 39ndash49 2006

[68] G Kolios B Gloumlckler A Gritsch A Morillo and G Eigen-berger ldquoHeat-integrated reactor concepts for hydrogen produc-tion by methane steam reformingrdquo Fuel Cells vol 5 no 1 pp52ndash65 2005

[69] A Haryanto S Fernando N Murali and S Adhikari ldquoCurrentstatus of hydrogen production techniques by steam reformingof ethanol a reviewrdquo Energy and Fuels vol 19 no 5 pp2098ndash2106 2005

[70] M Ni D Y C Leung and M K H Leung ldquoA review onreforming bio-ethanol for hydrogen productionrdquo InternationalJournal ofHydrogen Energy vol 32 no 15 pp 3238ndash3247 2007


[72] A N Fatsikostas and X E Verykios ldquoReaction network ofsteam reforming of ethanol over Ni-based catalystsrdquo Journal ofCatalysis vol 225 no 2 pp 439ndash452 2004

[73] J Llorca P Ramiacuterez de la Piscina J Sales and N Homs ldquoDirectproduction of hydrogen from ethanolic aqueous solutions overoxide catalystsrdquo Chemical Communications no 7 pp 641ndash6422001

[74] C Diagne H Idriss and A Kiennemann ldquoHydrogen pro-duction by ethanol reforming over RhCeO2-ZrO2 catalystsrdquoCatalysis Communications vol 3 no 12 pp 565ndash571 2002

[75] J Llorca P Ramiacuterez De La Piscina J A Dalmon J Salesand N Homs ldquoCo-free hydrogen from steam-reforming ofbioethanol over ZnO-supported cobalt catalysts effect of themetallic precursorrdquo Applied Catalysis B vol 43 no 4 pp355ndash369 2003

[76] E Vanhaecke A C Roger J C Vargas and A KiennemannldquoChallenges amp opportunities to bring hydrogen amp fuel cellsto an international marketrdquo in Proceedings of the1st EuropeanHydrogen Energy Conference p 2 Grenoble France September2003

[77] M S Batista R K S Santos E M Assaf J M Assaf and EA Ticianelli ldquoHigh efficiency steam reforming of ethanol bycobalt-based catalystsrdquo Journal of Power Sources vol 134 no1 pp 27ndash32 2004

[78] A Kaddouri and CMazzocchia ldquoA study of the inuence of thesynthesis conditions upon the catalytic properties of CoSiO2 orCoAl2O3 catalysts used for ethanol steam reformingrdquoCatalysisCommunications vol 5 no 6 pp 339ndash345 2004

[79] J Llorca J A Dalmon P Ramiacuterez De la Piscina and N HomsldquoIn situ magnetic characterisation of supported cobalt catalystsunder steam-reforming of ethanolrdquo Applied Catalysis A vol243 no 2 pp 261ndash269 2003

[80] F Haga T Nakajima H Miya and S Mishima ldquoCatalyticproperties of supported cobalt catalysts for steam reforming ofethanolrdquo Catalysis Letters vol 48 no 1-2 pp 223ndash227 1997

[81] H Idriss ldquoEthanol reactions over the surfaces of noblemetalcerium oxide catalystsrdquo Platinum Metals Review vol 48no 3 pp 105ndash115 2004

[82] J Bussi N Bespalko S Veiga A Amaya R Faccio and M CAbello ldquoe preparation and properties of Ni-La-Zr catalystsfor the steam reforming of ethanolrdquo Catalysis Communicationsvol 10 no 1 pp 33ndash38 2008

[83] G B Sun K Hidajat X S Wu and S Kawi ldquoA crucial role ofsurface oxygen mobility on nanocrystalline Y2O3 support foroxidative steam reforming of ethanol to hydrogen over NiY2O3catalystsrdquo Applied Catalysis B vol 81 no 3-4 pp 303ndash3122008

[84] E B Pereira N Homs S Marti J L G Fierro and P R de laPiscina ldquoOxidative steam-reforming of ethanol over CoSiO2Co-RhSiO2 and Co-RuSiO2 catalysts catalytic behavior anddeactivationregeneration processesrdquo Journal of Catalysis vol257 no 1 pp 206ndash214 2008

[85] H V Fajardo L F D Probst N L V Carreno I T S Garciaand A Valentini ldquoHydrogen production from ethanol steamreforming over NiCeO2 nanocomposite catalystsrdquo CatalysisLetters vol 119 no 3-4 pp 228ndash236 2007

[86] S Cavallaro ldquoEthanol steam reforming on RhAl2O3 CatalystsrdquoEnergy and Fuels vol 14 no 6 pp 1195ndash1199 2000

[87] M Toacuteth M Doumlmoumlk J Raskoacutex A Hancz and A ErdohelyildquoCatalysts a comparison between cobalt integration and cobaltImpregnationrdquo in Presented in the Technical Program Pisa ItalyMay 2004

[88] V Fierro V Klouz O Akdim and C Mirodatos ldquoOxidativereforming of biomass derived ethanol for hydrogen productionin fuel cell applicationsrdquo Catalysis Today vol 75 no 1ndash4 pp141ndash144 2002

[89] S Velu N Satoh C S Gopinath and K Suzuki ldquoOxidativereforming of bio-ethanol over CuNiZnAl mixed oxide catalystsfor hydrogen productionrdquo Catalysis Letters vol 82 no 1-2 pp145ndash152 2002

[90] M A Goula S K Kontou and P E Tsiakaras ldquoHydrogenproduction by ethanol steam reforming over a commercialPd120574120574-Al2O3 catalystrdquo Applied Catalysis B vol 49 no 2 pp135ndash144 2004

[91] P Sheng and H Idriss ldquoEthanol reactions over Au-RhCeO2catalysts Total decomposition and H2 formationrdquo Journal ofVacuum Science amp Technology A vol 22 no 4 article 1652 7pages 2004

[92] D Srinivas C V V Satyanarayana H S Potdar and PRatnasamy ldquoStructural studies on NiO-CeO2-ZrO2 catalystsfor steam reforming of ethanolrdquo Applied Catalysis A vol 246no 2 pp 323ndash334 2003


[93] N R C F Machado R C P Rizzo and P P S PeguenldquoPerformance of catalysts with Nb2O5 for hydrogen productionfrom ethanol steam reformingrdquo Acta Science vol 26 pp1637ndash1642 2002

[94] V V Galvita V D Belyaev V A Semikolenov P Tsiakaras AFrumin and V A Sobyanin ldquoEthanol decomposition over Pd-based catalyst in the presence of steamrdquo Reaction Kinetics andCatalysis Letters vol 76 no 2 pp 343ndash351 2002

[95] A Platon H S Roh D L King and Y Wang ldquoDeactivationstudies of RhCe08Zr02O2 catalysts in low temperature ethanolsteam reformingrdquo Topics in Catalysis vol 46 no 3-4 pp374ndash379 2007

[96] A Birot F Epron C Descorme andD Duprez ldquoEthanol steamreforming over RhCe119909119909Zr1minus119909119909O2 catalysts impact of the CO-CO2-CH4 interconversion reactions on the H2 productionrdquoApplied Catalysis B vol 79 no 1 pp 17ndash25 2008

[97] W Cai F Wang E Zhan A C Van Veen C Mirodatos andW Shen ldquoHydrogen production from ethanol over IrCeO2catalysts a comparative study of steam reforming partialoxidation and oxidative steam reformingrdquo Journal of Catalysisvol 257 no 1 pp 96ndash107 2008

[98] M Domok K Baan T Kecskes and A Erdohelyi ldquoPromotingmechanism of potassium in the reforming of ethanol onPtAl2O3 CatalystrdquoCatalysis Letters vol 126 no 1-2 pp 49ndash572008

[99] A C Bagasiannis P Panagiotopoulou and X E VerykiosldquoPrefacerdquo Topics in Catalysis vol 51 no 1ndash4 p 1 2008

[100] J Llorca N Homs J Sales and P Ramiacuterez de la Piscina ldquoEffi-cient production of hydrogen over supported cobalt catalystsfrom ethanol steam reformingrdquo Journal of Catalysis vol 209no 2 pp 306ndash317 2002

[101] J F da Costa Serra R Guil-Loacutepez and A Chica ldquoCoZnOand NiZnO catalysts for hydrogen production by bioethanolsteam reforming Inuence of ZnO support morphology on thecatalytic properties of Co and Ni active phasesrdquo InternationalJournal of Hydrogen Energy vol 13 no 143 pp 6709ndash67162010

[102] A Chica and S Sayas ldquoEffective and stable bioethanol steamreforming catalyst based on Ni and Co supported on all-silicadelaminated ITQ-2 zeoliterdquo Catalysis Today vol 146 no 1-2pp 37ndash43 2009

[103] F C Campos-Skrobot R C P Rizzo-Domingues N RC Fernandes-Machado and M P Cantatildeo ldquoNovel zeolite-supported rhodium catalysts for ethanol steam reformingrdquoJournal of Power Sources vol 183 no 2 pp 713ndash716 2008

[104] H Inokawa S Nishimoto Y Kameshima and M MiyakeldquoDifference in the catalytic activity of transition metals andtheir cations loaded in zeolite y for ethanol steam reformingrdquoInternational Journal of Hydrogen Energy vol 35 no 21 pp11719ndash11724 2010

[105] J F da Costa Serra and A Chica ldquoBioethanol steam reformingon CoITQ-18 catalyst effect of the crystalline structure of thedelaminated zeolite ITQ-18rdquo International Journal of HydrogenEnergy vol 36 no 6 pp 3862ndash3869 2011

[106] A Corma V Fornes and U Dıaz ldquoITQ-18 a new delam-inated stable zeoliterdquo Chemical Communications no 24 pp2642ndash2643 2001

[107] B S Kwak J S Lee J S Lee B-H Choi M J Ji and M KangldquoHydrogen-rich gas production from ethanol steam reform-ing over NiGaMgZeolite Y catalysts at mild temperaturerdquoApplied Energy vol 88 no 12 pp 4366ndash4375 2011

[108] H Inokawa S Nishimoto Y Kameshima and M MiyakeldquoPromotion of H2 production from ethanol steam reforming byzeolite basicityrdquo International Journal of Hydrogen Energy vol36 no 23 pp 15195ndash15202 2011

[109] J S Lee J Kim and M Kang ldquoHydrogen production fromethanol steam reforming over SnO2-K2Ozeolite Y catalystrdquoBulletin of the Korean Chemical Society vol 32 no 6 pp1912ndash1920 2011

[110] C T Kresge M E Leonowicz W J Roth J C Vartuli and J SBeck ldquoOrdered mesoporous molecular sieves synthesized by aliquid-crystal template mechanismrdquo Nature vol 359 no 6397pp 710ndash712 1992

[111] S Inagaki Y Fuhushima and K J Kuroda ldquoSynthesis of highlyordered mesoporous materials from a layered polysilicaterdquoJournal of the Chemical Society Chemical Communications no8 pp 680ndash682 1993

[112] Y Tao H Kanoh L Abrams and K Kaneko ldquoMesopore-modied zeolites preparation characterization and applica-tionsrdquo Chemical Reviews vol 106 no 3 pp 896ndash910 2006

[113] J Perez-Ramirez C H Christensen K Egeblad C H Chris-tensen and J C Groen ldquoHierarchical zeolites enhancedutilisation of microporous crystals in catalysis by advances inmaterials designrdquo CChemical Society Reviews vol 37 no 11pp 2530ndash2542 2008

[114] M Ogura ldquoTowards realization of a micro- and mesoporouscomposite silicate catalystrdquo Catalysis Surveys from Asia vol 12no 1 pp 16ndash27 2008

[115] A Corma ldquoApplication of zeolites in uid catalytic cracking andrelated processesrdquo Studies in Surface Science and Catalysis vol49 pp 49ndash67 1989

[116] J C Groen J A Moulijn and J Peacuterez-Ramirez ldquoDesilicationon the controlled generation of mesoporosity in MFI zeolitesrdquoJournal of Materials Chemistry vol 16 no 22 pp 2121ndash21312006

[117] D Verboekend and J Perez-Ramirez ldquoDesign of hierarchicalzeolite catalysts by desilicationrdquo Catal Science amp Tecnology vol1 no 6 pp 879ndash890 2011

[118] J C Groen L A A Peffer J A Moulijn and J Peacuterez-Ramiacuterez ldquoMesoporosity development in ZSM-5 zeolite uponoptimized desilication conditions in alkaline mediumrdquo Colloidsand Surfaces A vol 24 no 1ndash3 pp 53ndash58 2004

[119] J C Groen R Caicedo-Realpe S Abelloacute and J Peacuterez-Ramirez ldquoMesoporous metallosilicate zeolites by desilicationon the generic pore-inducing role of framework trivalentheteroatomsrdquo Materials Letters vol 63 no 12 pp 1037ndash10402009

[120] Y TaoHKanoh andKKaneko ldquoDevelopments and structuresof mesopores in alkaline-treated ZSM-5 zeolitesrdquo Adsorptionvol 12 no 5-6 pp 309ndash316 2006

[121] M M Otten M J Clayton and H H Lamb ldquoPlatinum-mordenite catalysts for n-hexane isomerization characteriza-tion by X-Ray absorption spectroscopy and chemical probesrdquoJournal of Catalysis vol 149 no 1 pp 211ndash222 1994

[122] B T Carvill B A Lerner B J Adelman D C Tomazackand V M W Sachtler ldquoIncreased catalytic activity caused bylocal destruction of linear zeolite channels effect of reductiontemperature on heptane conversion over platinum supportedin H-mordeniterdquo Journal of Catalysis vol 144 no 1 pp 1ndash81993

[123] M S Holm E Taarning K Egeblad and C H ChristensenldquoCatalysis with hierarchical zeolitesrdquo Catalysis Today vol 168no 1 pp 3ndash16 2011


[124] D H Park S S Kim HWang et al ldquoSelective petroleum ren-ing over a zeolite catalyst with small intracrystal mesoporesrdquoAngewandte Chemie vol 48 no 41 pp 7645ndash7648 2009

[125] H J Park K H Park J K Jeon et al ldquoProduction of phenolicsand aromatics by pyrolysis of miscanthusrdquo Fuel vol 97 pp379ndash384 2012

[126] A J Foster J Jae Y T Cheng G W Huber and R F LoboldquoOptimizing the aromatic yield and distribution from catalyticfast pyrolysis of biomass over ZSM-5rdquo Applied Catalysis A vol423-424 pp 154ndash161 2012

[127] G T Neumann and J C Hicks ldquoNovel hierarchical cerium-incorporatedMFI zeolite catalysts for the catalytic fast pyrolysisof lignocellulosic biomassrdquo ACS Catalysis vol 2 no 4 pp642ndash646 2012

[128] M J Jeon S S Kim K J Jeon et al ldquoCatalytic pyrolysis ofwaste rice husk overmesoporousmaterialsrdquoNanoscale ResearchLetters vol 7 article 18 2012

[129] V Paixao A P Carvalho J Rocha A Fernandes and AMartins ldquoModication of MOR by desilication treatmentsstructural textural and acidic characterizationrdquo Micro andMesoporous Materials vol 131 no 1ndash3 pp 350ndash357 2010

[130] J F da Costa Serra M T Navarro F Rey and A Chicaldquoioethanol steam reforming on Ni-based modied mordeniteEffect of mesoporosity acid sites and alkaline metalsrdquo Interna-tional Journal of Hydrogen Energy vol 37 no 8 pp 7101ndash71082012

[131] R D Cortright R R Davda and J A Dumesic ldquoHydrogenfrom catalytic reforming of biomass-derived hydrocarbons inliquid waterrdquo Nature vol 418 no 6901 pp 964ndash967 2002

[132] R R Davda J W Shabaker G W Huber R D Cortrightand J A Dumesic ldquoA review of catalytic issues and processconditions for renewable hydrogen and alkanes by aqueous-phase reforming of oxygenated hydrocarbons over supportedmetal catalystsrdquo Applied Catalysis B vol 56 no 1-2 pp171ndash186 2005

[133] GW Huber and J A Dumesic ldquoAn overview of aqueous-phasecatalytic processes for production of hydrogen and alkanes ina bioreneryrdquo Catalysis Today vol 111 no 1-2 pp 119ndash1322006

[134] Z Tang J Monroe J Dong T Nenoff and D WeinkaufldquoPlatinum-loaded NaY zeolite for aqueous-phase reforming ofmethanol and ethanol to hydrogenrdquo Industrial and EngineeringChemistry Research vol 48 no 5 pp 2728ndash2733 2009

[135] N S Lewis and D G Nocera ldquoPowering the planet chem-ical challenges in solar energy utilizationrdquo Proceedings of theNational Academy of Sciences of the United States of Americavol 103 no 43 pp 15729ndash15735 2006

[136] X Chen S Shen L Guo and S S Mao ldquoSemiconductor-based photocatalytic hydrogen generationrdquo Chemical Reviewsvol 110 no 11 pp 6503ndash6570 2010

[137] A Kudo and YMiseki ldquoHeterogeneous photocatalyst materialsfor water splittingrdquo Chemical Society Reviews vol 38 no 1 pp253ndash278 2009

[138] A Fujishima and K Honda ldquoElectrochemical photolysis ofwater at a semiconductor electroderdquo Nature vol 238 no 5358pp 37ndash38 1972

[139] A Kudo H Kato and I Tsuji ldquoStrategies for the developmentof visible-light-driven photocatalysts for water splittingrdquoChem-istry Letters vol 33 no 12 pp 1534ndash1539 2004

[140] K Domen S Naito T Onishi and K Tamaru ldquoPhotocatalyticdecomposition of liquid water on a NiOSrTiO3 catalystrdquo Chem-ical Physics Letters vol 92 no 4 pp 433ndash434 1982

[141] Y Inoue T Kubokawa and K Sato ldquoPhotocatalytic activityof sodium hexatitanate Na2Ti6O13 with a tunnel structurefor decomposition of waterrdquo Journal of the Chemical SocietyChemical Communications no 19 pp 1298ndash1299 1990

[142] T Takata Y Furumi K Shinohara et al ldquoPhotocatalyticdecomposition of water on spontaneously hydrated layered per-ovskitesrdquo Chemistry of Materials vol 9 no 5 pp 1063ndash10641997

[143] A Kudo K Sayama A Tanaka et al ldquoNickel-loaded K4Nb6O17photocatalyst in the decomposition of H2O into H2 and O2structure and reaction mechanismrdquo Journal of Catalysis vol120 no 2 pp 337ndash352 1989

[144] K Sayama A Tanaka K Domen K Maruya and TOnishi ldquoPhotocatalytic decomposition of water over platinum-intercalated K4Nb6O17rdquo Journal of Physical Chemistry vol 95no 3 pp 1345ndash1348 1991

[145] A Kudo and H Kato ldquoPhotocatalytic decomposition of waterinto H2 and O2 over novel photocatalyst K3Ta3Si2O13 withpillared structure consisting of three TaO6 chainsrdquo ChemistryLetters vol 26 no 9 pp 867ndash868 1997

[146] T Ishihara H Nishiguchi K Fukamachi and Y Takita ldquoEffectsof acceptor doping to KTaO3 on photocatalytic decompositionof pure H2Ordquo Journal of Physical Chemistry B vol 103 no 1pp 1ndash3 1999

[147] A KudoH Kato and SNakagawa ldquoWater splitting intoH2 andO2 on New Sr2M2O7 (M=Nb and Ta) photocatalysts with lay-ered perovskite structures factors affecting the photocatalyticactivityrdquo e Journal of Physical Chemistry B vol 104 no 3pp 571ndash575 2000

[148] H Kato and A Kudo ldquoWater splitting into H2 and O2 on alkalitantalate photocatalysts ATaO3 (A = Li Na and K)rdquoe Journalof Physical Chemistry B vol 105 no 19 pp 4285ndash4292 2001

[149] A Kudo K Asakura and H Kato ldquoHighly ecient watersplitting into H2 and O2 over lanthanum-doped NaTaO3 pho-tocatalysts with high crystallinity and surface nanostructurerdquoJournal of the American Chemical Society vol 125 no 10 pp3082ndash3089 2003

[150] Z Zou J Ye K Sayama and H Arakawa ldquoDirect splitting ofwater under visible light irradiation with an oxide semiconduc-tor photocatalystrdquoNature vol 414 no 6864 pp 625ndash627 2001

[151] M Machida J I Yabunaka and T Kijima ldquoSynthesis and pho-tocatalytic property of layered perovskite tantalates RbLnTa2O7(Ln = La Pr Nd and Sm)rdquo Chemistry of Materials vol 12 no3 pp 812ndash817 2000

[152] H Kato and A Kudo ldquoVisible-light-response and photocat-alytic activities of TiO2and SrTiO3 photocatalysts codoped withantimony and chromiumrdquoe Journal of Physical Chemistry Bvol 106 no 19 pp 5029ndash5034 2002

[153] T Ishii H Kato and A Kudo ldquoH2 evolution from an aqueousmethanol solution on SrTiO3 photocatalysts codoped withchromium and tantalum ions under visible light irradiationrdquoJournal of Photochemistry and Photobiology A vol 163 no 1-2 pp 181ndash186 2004

[154] I Tsuji H Kato H Kobayashi andA Kudo ldquoPhotocatalytic H2evolution reaction from aqueous solutions over band structure-controlled (AgIn)119909119909Zn2(1minus119909119909119909S2 solid solution photocatalysts withvisible-light response and their surface nanostructuresrdquo Jour-nal of the American Chemical Society vol 126 no 41 pp13406ndash13413 2004

[155] I Tsuji H Kato and A Kudo ldquoPhotocatalytic hydrogen evolu-tion on ZnSminusCuInS2minusAgInS2 solid solution photocatalysts with


wide visible light absorption bandsrdquoChemistry ofMaterials vol18 no 7 pp 1969ndash1975 2006

[156] D Yamasita T Takata M Hara J N Kondo and K DomenldquoRecent progress of visible-light-driven heterogeneous photo-catalysts for overall water splittingrdquo Solid State Ionics vol 172no 1ndash4 pp 591ndash595 2004

[157] R Niishiro H Kato and A Kudo ldquoNickel and either tantalumor niobium-codoped TiO2 and SrTiO3 photocatalysts withvisible-light response for H2 or O2 evolution from aqueoussolutionsrdquo Physical Chemistry Chemical Physics vol 7 no 10pp 2241ndash2245 2005

[158] I Tsuji and A Kudo ldquoH2 evolution from aqueous sultesolutions under visible-light irradiation over Pb and halogen-codoped ZnS photocatalystsrdquo Journal of Photochemistry andPhotobiology A vol 156 no 1ndash3 pp 249ndash252 2003

[159] O Diwald T L ompson E G Goralski S D Walck andJ T Yates ldquoe effect of nitrogen ion implantation on thephotoactivity of TiO2 rutile single crystalsrdquo Journal of PhysicalChemistry B vol 108 no 1 pp 52ndash57 2004

[160] R Konta T Ishii H Kato and A Kudo ldquoPhotocatalyticactivities of noble metal ion doped SrTiO3 under visible lightirradiationrdquo Journal of Physical Chemistry B vol 108 no 26pp 8992ndash8995 2004

[161] I Tsuji H Kato and A Kudo ldquoVisible-light-induced H2evolution from an aqueous solution containing sulde andsulte over a ZnS-CuInS2-AgInS2 solid-solution photocatalystrdquoAngewandte Chemie vol 44 no 23 pp 3565ndash3568 2005

[162] T L ompson and J T Yates ldquoSurface science studies ofthe photoactivation of TiO2 new photochemical processesrdquoChemical Reviews vol 106 no 10 pp 4428ndash4453 2006

[163] J L Gole J D Stout C Burda Y Lou and X Chen ldquoHighlyefficient formation of visible light tunable TiO2minus119909119909N119909119909 photocat-alysts and their transformation at the nanoscalerdquo Journal ofPhysical Chemistry B vol 108 no 4 pp 1230ndash1240 2004

[164] C Di Valentin G Pacchioni and A Selloni ldquoOrigin of thedifferent photoactivity of N-doped anatase and rutile TiO2rdquoPhysical Review B vol 70 Article ID 18202 4 pages 2004

[165] G Hitoki A Ishikawa T Takata J N Kondo M Hara andK Domen ldquoTa3N5 as a novel visible light-driven photocatalyst(120582120582 120582 600 nm)rdquo Chemistry Letters no 7 pp 736ndash737 2002

[166] A Kasahara K Nukumizu G Hitoki et al ldquoPhotoreactionson LaTiO2N under visible light irradiationrdquo Journal of PhysicalChemistry A vol 106 no 29 pp 6750ndash6753 2002

[167] H Kato K Asakura and A Kudo ldquoHighly efficient watersplitting into H2 and O2 over Lanthanum-Doped NaTaO3 pho-tocatalysts with high crystallinity and surface nanostructurerdquoJournal of the American Chemical Society vol 125 no 10 pp3082ndash3089 2003

[168] W Shangguan and A Yoshida ldquoPhotocatalytic hydrogen evo-lution from water on nanocomposites incorporating cadmiumsulde into the interlayerrdquo Journal of Physical Chemistry B vol106 no 47 pp 12227ndash12230 2002

[169] A Koca and M Sahin ldquoPhotocatalytic hydrogen productionby direct sun light from suldesulte solutionrdquo InternationalJournal of Hydrogen Energy vol 27 no 4 pp 363ndash367 2002

[170] G Milczarek A Kasuya S Mamykin T Arai K Shinodaand K Tohji ldquoOptimization of a two-compartment photoelec-trochemical cell for solar hydrogen productionrdquo InternationalJournal of Hydrogen Energy vol 28 no 9 pp 919ndash926 2003

[171] J R Plunkett and United States Energy Information Adminis-tration International Energy Outlook and Projections NovaScience Hauppauge NY USA 2011


[173] M Ni M K H Leung D Y C Leung and K SumathyldquoA review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen productionrdquo Renewable andSustainable Energy Reviews vol 11 no 3 pp 401ndash425 2007

[174] M Matsuoka M Kitano M Takeuchi K Tsujimaru M Anpoand J M omas ldquoPhotocatalysis for new energy productionRecent advances in photocatalytic water splitting reactions forhydrogen productionrdquo Catalysis Today vol 122 no 1-2 pp51ndash61 2007

[175] T Bak J Nowotny M Rekas and C C Sorrell ldquoPhoto-electrochemical hydrogen generation from water using solarenergy Materials-related aspectsrdquo International Journal ofHydrogen Energy vol 27 no 10 pp 991ndash1022 2002

[176] Y A Shaban and S U M Khan ldquoVisible light active carbonmodied n-TiO2 for efficient hydrogen production by pho-toelectrochemical splitting of waterrdquo International Journal ofHydrogen Energy vol 33 no 4 pp 1118ndash1126 2008

[177] H Y Lin T H Lee and C Y Sie ldquoPhotocatalytic hydrogenproduction with nickel oxide intercalated K4Nb6O17 undervisible light irradiationrdquo International Journal of HydrogenEnergy vol 33 no 15 pp 4055ndash4063 2008

[178] H Y Lin Y F Chen and Y W Chen ldquoWater splitting reactionon NiOInVO4 under visible light irradiationrdquo InternationalJournal of Hydrogen Energy vol 32 no 1 pp 86ndash92 2007

[179] P S Lunawat S Senapati R Kumar and N M GuptaldquoVisible light-induced splitting of water using CdS nanocrys-tallites immobilized over water-repellant polymeric surfacerdquoInternational Journal of Hydrogen Energy vol 32 no 14 pp2784ndash2790 2007

[180] M Sathish B Viswanathan and R P Viswanath ldquoAlternatesynthetic strategy for the preparation of CdS nanoparticlesand its exploitation for water splittingrdquo International Journal ofHydrogen Energy vol 31 no 7 pp 891ndash898 2006

[181] N Koriche A Bouguelia A Aider and M Trari ldquoPhotocat-alytic hydrogen evolution over delafossite CuAlO2rdquo Interna-tional Journal of Hydrogen Energy vol 30 no 7 pp 693ndash6992005

[182] J Ye Z Zou and A Matsushita ldquoA novel series of watersplitting photocatalysts NiM2O6 (M=Nb Ta) active undervisible lightrdquo International Journal of Hydrogen Energy vol 28no 6 pp 651ndash655 2003

[183] Y Bessekhouad andMTrari ldquoPhotocatalytic hydrogen produc-tion from suspension of spinel powders AMn2O4(A =Cu andZn)rdquo International Journal of Hydrogen Energy vol 27 no 4pp 357ndash362 2002

[184] P K Dutta and W Turbeville ldquoIntrazeolitic photoinducedredox reactions between Ru(bpy)2+3 and methylviologenrdquo Jour-nal of Physical Chemistry vol 96 no 23 pp 9410ndash9416 1992

[185] H Yamashita Y Fujii Y Ichihashi et al ldquoSelective formationof CH3OH in the photocatalytic reduction of CO2 with H2Oon titanium oxides highly dispersed within zeolites and meso-porous molecular sievesrdquo Catalysis Today vol 45 no 1ndash4 pp221ndash227 1998

[186] M Anpo H Yamashita Y Ichihashi Y Fujii and M HondaldquoPhotocatalytic reduction of CO2 with H2O on titanium oxidesanchored within micropores of zeolites effects of the structureof the active sites and the addition of Ptrdquo Journal of PhysicalChemistry B vol 101 no 14 pp 2632ndash2636 1997


[187] S G Zhang Y Fujii H Yamashita K Koyano T Tatsumiand M Anpo ldquoPhotocatalytic reduction of CO2 with H2O onTi-MCM-41 and Ti-MCM-48 mesoporous zeolites at 328KrdquoChemistry Letters no 7 pp 659ndash660 1997

[188] M Anpo M Matsuoka Y Shioya et al ldquoPreparation and char-acterization of theCu+ZSM-5 catalyst and its reactionwithNOunderUV irradiation at 275K In situ photoluminescence EPRand FT-IR investigationsrdquo Journal of Physical Chemistry vol 98no 22 pp 5744ndash5750 1994

[189] M Anpo and H Yamashita ldquoPhotochemistry of surface speciesanchored on solid surfacesrdquo in Surface Photochemistry MAnpo Ed p 117 Wiley London UK 1996

[190] H Yamashita Y Ichihashi M Anpo M Hashimoto C Louisand M Che ldquoPhotocatalytic decomposition of NO at 275K ontitanium oxides included within Y-zeolite cavities the structureand role of the active sitesrdquo e Journal of Physical Chemistryvol 100 no 40 pp 16041ndash16044 1996

[191] H Chen A Matsumoto N Nishimiya and K TsutsumildquoPreparation and characterization of TiO2 incorporated Y-zeoliterdquo Colloids and Surfaces A vol 157 no 1ndash3 pp 295ndash3051999

[192] X Liu K K Lu and J K omas ldquoEncapsulation of TiO2in zeolite Yrdquo Chemical Physics Letters vol 195 no 2-3 pp163ndash168 1992

[193] X Liu K K Lu and J K omas ldquoPreparation characteriza-tion and photoreactivity of titanium(IV) oxide encapsulated inzeolitesrdquo Journal of the Chemical Society vol 89 pp 1861ndash18651993

[194] Y Kim and M Yoon ldquoTiO2Y-Zeolite encapsulatingintramolecular charge transfer molecules a new photocatalystfor photoreduction of methyl orange in aqueous mediumrdquoJournal of Molecular Catalysis A vol 168 no 1-2 pp 257ndash2632000

[195] X Chen and S S Mao ldquoTitanium dioxide nanomate-rials synthesis properties modications and applicationsrdquoChemical Reviews vol 107 no 7 pp 2891ndash2959 2007

[196] S Ikeda A Tanaka K Shinohara et al ldquoEffect of the particlesize for photocatalytic decomposition of water on Ni-loadedK4Nb4O17rdquoMicroporous Materials vol 9 no 5-6 pp 253ndash2581997

[197] M C Hidalgo M Aguilar M Maicu J A Naviacuteo and GColoacuten ldquoHydrothermal preparation of highly photoactive TiO2nanoparticlesrdquo Catalysis Today vol 129 no 1-2 pp 50ndash582007

[198] A Testino I R Bellobono V Buscaglia et al ldquoOptimizing thephotocatalytic properties of hydrothermal TiO2 by the controlof phase composition and particle morphology A systematicapproachrdquo Journal of the American Chemical Society vol 129no 12 pp 3564ndash3575 2007

[199] A Datta A Priyam S N Bhattacharyya K K Mukherjea andA Saha ldquoTemperature tunability of size in CdS nanoparticlesand size dependent photocatalytic degradation of nitroaromat-icsrdquo Journal of Colloid and Interface Science vol 322 no 1 pp128ndash135 2008

[200] S Y Chae M K Park S K Lee T Y Kim S K Kim andW I Lee ldquoPreparation of size-controlled TiO2 nanoparticlesand derivation of optically transparent photocatalytic lmsrdquoChemistry of Materials vol 15 no 17 pp 3326ndash3331 2003

[201] G Liu C Sun H G Yang et al ldquoNanosized anatase TiO2single crystals for enhanced photocatalytic activityrdquo ChemicalCommunications vol 46 no 5 pp 755ndash757 2010

[202] Y Lee T Watanabe T Takata M Hara M Yoshimura and KDomen ldquoHydrothermal synthesis of ne NaTaO3 powder as ahighly efficient photocatalyst for overall water splittingrdquoBulletinof theChemical Society of Japan vol 80 no 2 pp 423ndash428 2007

[203] Z Zhang C C Wang R Zakaria and J Y Ying ldquoRole of parti-cle size in nanocrystalline TiOi-based photocatalystsrdquo Journal ofPhysical Chemistry B vol 102 no 52 pp 10871ndash10878 1998

[204] W Sun S Zhang Z Liu C Wang and Z Mao ldquoStudies onthe enhanced photocatalytic hydrogen evolution over PtPEG-modied TiO2 photocatalystsrdquo International Journal of Hydro-gen Energy vol 33 no 4 pp 1112ndash1117 2008

[205] D W Bahnemann C Kormann and M R Hoffmann ldquoPrepa-ration and characterization of quantum size zinc oxide adetailed spectroscopic studyrdquo Journal of Physical Chemistry vol91 no 14 pp 3789ndash3798 1987

[206] A J Hoffman E R Carraway and M R Hoffmann ldquoPho-tocatalytic production of H2O2 and organic peroxides onquantum-sized semiconductor colloidsrdquo Environmental Scienceamp Technology vol 28 no 5 pp 776ndash785 1994

[207] A J Hoffman G Mills H Yee and M R Hoffmann ldquoQ-sizedcadmium sulde synthesis characterization and efficiency ofphotoinitiation of polymerization of several vinylicmonomersrdquoe Journal of Physical Chemistry vol 96 no 13 pp 5546ndash55521992

[208] A J Hoffman H Yee G Mills and M R Hoffmann ldquoQ-sizedcadmium sulde synthesis characterization and efficiency ofphotoinitiation of polymerization of several vinylicmonomersrdquoe Journal of Physical Chemistry vol 96 no 13 pp 5540ndash55521992

[209] M A Fox and T L Pettit ldquoPhotoactivity of zeolite-supportedcadmium sulde hydrogen evolution in the presence of sacri-cial donorsrdquo Langmuir vol 5 no 4 pp 1056ndash1061 1989

[210] M Warrier M K F Lo H Monbouquette and M AGarcia-Garibay ldquoPhotocatalytic reduction of aromatic azides toamines using CdS and CdSe nanoparticlesrdquo Photochemical andPhotobiological Sciences vol 3 no 9 pp 859ndash863 2004

[211] M Sathish B Vishwanathan and R P Vishwanath ldquoAlternatesynthetic strategy for the preparation of CdS nanoparticlesand its exploitation for water splittingrdquo International Journal ofHydrogen Energy vol 31 no 7 pp 891ndash898 2006

[212] S Y Ryu W Balcerski T K Lee and M R HoffmannldquoPhotocatalytic production of hydrogen fromwater with visiblelight using hybrid catalysts of CdS attached tomicroporous andmesoporous silicasrdquo Journal of Physical Chemistry C vol 111no 49 pp 18195ndash18203 2007

[213] S Y Ryu J Choi W Balcerski T K Lee and M R HoffmannldquoPhotocatalytic production of H2 on nanocomposite catalystsrdquoIndustrial and Engineering Chemistry Research vol 46 no 23pp 7476ndash7488 2007

[214] P Yue and F Khan ldquoMethods for increasing photo-assistedproduction of hydrogen over titanium exchanged zeolitesrdquoInternational Journal of Hydrogen Energy vol 16 no 9 pp609ndash613 1991

[215] G Guan T Kida K Kusakabe K Kimura X Fang and T MaldquoPhotocatalytic H2 evolution under visible light irradiation onCdSETS-4 compositerdquo Chemical Physics Letters vol 385 no3-4 pp 319ndash322 2004

[216] G Guan T Kida K Kusakabe et al ldquoPhotocatalytic H2 evolu-tion under visible light irradiation on CdSETS-4 compositerdquoChemical Physics Letters vol 385 no 3-4 pp 319ndash322 2004


[217] N Dubey S S Rayalu N K Labhsetwar and S DevottaldquoVisible light active zeolite-based photocatalysts for hydro-gen evolution from waterrdquo International Journal of HydrogenEnergy vol 33 no 21 pp 5958ndash5966 2008

[218] J CWhite and P K Dutta ldquoAssembly of nanoparticles in zeoliteY for the photocatalytic generation of hydrogen fromwaterrdquoeJournal of Physical Chemistry C vol 115 no 7 pp 2938ndash29472011


F 1 Representation of the projection of the frameworkstructure of zeolites (a) T-site connectivity only (b) ball and stick(c) space lling and (d) (Si Al) O4 tetrahedra

Zeolite framework is formed from corner sharing[SiO4]

4minus and [AlO4]5minus tetrahedra which dene the cavities

and channels in which the cations can be found coordinatingto the framework oxygens andor water molecules Figure 1shows the different representations typical of those used inthe literature of the framework of one zeolite

e ways to combine each tetrahedron are extremelywide e structure of the zeolite is dened by its cornersharing tetrahedra of [SiO4]

4minus and [AlO4]5minus and these are

called secondary building units (SBUs) [12] (see Figure 2)e utility of these constructions is that the angles and

distances of zeolites are contained in these SBUs so thestructural characterization of one zeolite could be carried outby examining the SBUs that it containsere are 16 differentSBUs and the structure of each zeolite can be described usingone or more of these SBUs

In zeolites the organization of TO4 tetrahedra can resultin the formation of rings with different numbers of T atoms(Si Al) e most common rings are 4-T 6-T 8-T 10-T and12-T however zeolitic structures containing 14 18 and 30member rings have been also synthesized [13ndash20]e size ofthemicropores of the zeolite varies depending on the numberof members in the rings between 4 and 12Aring On rings T-O-T angles vary mostly in the range 130∘ndash180∘e exibility ofthis angle is one of the most important factors determiningthe huge variety of existing zeolites

12 Properties Zeolites may act as molecular sieves thusone of their main physical properties is the porosity emicroporous properties of zeolites make them present anextremely large internal surface area in relation to theirexternal surface Micropores are open to the outside allowing

o

o

o o

oo o

o o o

o

o

oo

o o

o ooo

o

o

o o

o

o o

ooo oo o

o

o o

o

o

ooo

oo

o o o o

oo

o

oo

ooo

o o o

o

o oo o

o

o

o o o

o

o

o

o o

o

o

o

o o

oo

o

oo

o o

o

o o

o

o

oo

oo

o

o

o oo o

o

oo

o oo

oo

o

o

o

o

4 6 8 5

4-4 6-6 8-8 6-2

4-1 6-1 5-2 5-1

4-1 4-4-1 5-3 Spiro-5

F 2 Basic secondary units (BSUs) to dene the structure ofzeolites

the transference of matter between the intracrystalline spaceand the surrounding environment

Tridimensional networks of well-dened micropores canact as reaction channels whose activity and selectivity will beenhanced by introducing active sites e presence of strongelectric elds and controllable adsorption properties withinthe pores will produce a unique type of catalyst which byitself can be considered as a catalytic microreactor

e size of the pores and channels of zeolites rangesbetween 4 and 12Aring [21] and the channel system may bemono- bi- or three-directional Table 1 shows the classi-cation of zeolites based on the number of tetrahedrals thatform the pores and give access to the intracrystalline space[22ndash25]

Summarizing the main properties of zeolites are asfollows

(i) high surface area(ii) molecular dimensions of the pores(iii) high adsorption capacity(iv) partitioning of reactantproducts(v) possibility of modulating the electronic properties of

the active sites(vi) possibility for preactivating the molecules when in


13 Applications Zeolites have a variety of industrial applica-tions especially as ion exchangers adsorbents and chemicalscatalysts























C2H5OH + 3H2O ⟶2CO2 + 6H2

ΔH0 = +1733 kJmol(2)

C2H5OH + 15O2 ⟶ 2CO2 + 3H2




(4)







OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

Co or Ni particles

12 MR

10 MR






Swollen

material

Calcined

NU6(2)

NU6(1)

Sonication

ITQ-18

Calcined Co0

CTMA+
































Zeolite Y

Ga2O3

Ni

Carbon

MgO

NiO

Inte

nsi

ty (

au

)









5 20 40 60 80 100















MOR original

(a)

MOR modified

(b)











CB

VB

H+

H2

minus

+

4H+


0 V

+123 V

eminus

h+

O2H2O

2H2O + 4h+

rarr O2uarr + 4H+



H2O + h120584120584120584 H2 +12O2 (7)



bull (8)






















3 Conclusions















References

























































































































































































































































C2H5OH + 3H2O ⟶2CO2 + 6H2

ΔH0 = +1733 kJmol(2)

C2H5OH + 15O2 ⟶ 2CO2 + 3H2




(4)







OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

Co or Ni particles

12 MR

10 MR






Swollen

material

Calcined

NU6(2)

NU6(1)

Sonication

ITQ-18

Calcined Co0

CTMA+
































Zeolite Y

Ga2O3

Ni

Carbon

MgO

NiO

Inte

nsi

ty (

au

)









5 20 40 60 80 100















MOR original

(a)

MOR modified

(b)











CB

VB

H+

H2

minus

+

4H+


0 V

+123 V

eminus

h+

O2H2O

2H2O + 4h+

rarr O2uarr + 4H+



H2O + h120584120584120584 H2 +12O2 (7)



bull (8)






















3 Conclusions















References





































































































































































































































OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

Co or Ni particles

12 MR

10 MR






Swollen

material

Calcined

NU6(2)

NU6(1)

Sonication

ITQ-18

Calcined Co0

CTMA+
































Zeolite Y

Ga2O3

Ni

Carbon

MgO

NiO

Inte

nsi

ty (

au

)









5 20 40 60 80 100















MOR original

(a)

MOR modified

(b)











CB

VB

H+

H2

minus

+

4H+


0 V

+123 V

eminus

h+

O2H2O

2H2O + 4h+

rarr O2uarr + 4H+



H2O + h120584120584120584 H2 +12O2 (7)



bull (8)






















3 Conclusions















References





























































































































































































































































Zeolite Y

Ga2O3

Ni

Carbon

MgO

NiO

Inte

nsi

ty (

au

)









5 20 40 60 80 100















MOR original

(a)

MOR modified

(b)











CB

VB

H+

H2

minus

+

4H+


0 V

+123 V

eminus

h+

O2H2O

2H2O + 4h+

rarr O2uarr + 4H+



H2O + h120584120584120584 H2 +12O2 (7)



bull (8)






















3 Conclusions















References













































































































































































































































MOR original

(a)

MOR modified

(b)











CB

VB

H+

H2

minus

+

4H+


0 V

+123 V

eminus

h+

O2H2O

2H2O + 4h+

rarr O2uarr + 4H+



H2O + h120584120584120584 H2 +12O2 (7)



bull (8)






















3 Conclusions















References






















































































































































































































































3 Conclusions















References










































































































































































































































References



































































































































































































































reviewarticle zeolites:promisedmaterialsfor

Documents