Catalysis

Catalysis ApplicationsCatalysis Applications

World catalystsWorld catalysts• 9 G$ business in 1999• 24% for Refining, 24% for Chemicals,

23% for Polymers, 29% for Environment

oxidation

According to Dept. Energy, USA, in 2003

Catalysis & Catalytic processes are

•responsible for about 20% of the U.S. gross domestic product (all goods and services)

• the keys to future gains in energy efficiency, environmental stewardship and attendant economic prosperity for the country

The twelve principles of Green Chemistry1. It is better to prevent waste than to treat or clean up

waste after it is formed.

2. Synthesis methods must be designed to maximize the incorporation of all materials used in the process into the final product.

3. Whenever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

4. - - - -

9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

10.- - - -

Early History of Catalysis

•Neolithic age (新石器時代 ~5000B.C.)

Biocatalytic fermentation in wine manufacture

•500B.C.

Soap manufacture (hydrolysis of animal fats with potash lye)

•1500A.C.

Alchemists formed sulfuric acid by a mysterious catalytic process

•1831

Pelegrine Phillips (a Bristol vinegar manufacturer) obtained the 1st known patent in catalysis for the reaction

SO2 + air → SO3 (Pt sponge as catalyst)

The catalyst used now-a-day is V2O5/ SiO2

•1835

J.J. Berzelius coined the word “catalysis”

Greek words “cata”means “down”

“lysis”means “split”or “break”

“This new force, which is unknown until now, is common to both organic and inorganic nature. I do not believe that it is a force completely independent of electrochemical affinities; … It is more convenient to give this force a separate name. I would therefore call this the catalytic force. I would furthermore, call the decomposition of substances resulting from this force catalysis, just as the decomposition of substances resulting from chemical affinity is calledanalysis.”

•1880 Carl Groebeaccidentally broke a thermometer while stirring a mixture of hot naphthalene and H2SO4

⇒ phthalic anhydride & phthalic acid⇒ dye chemistry

•1899 Arrhenius equation k = A exp(-Ea/RT)

•1903 Ostward process

2NH3 + 7/2 O2 → 2NO2 + 3 H2O (Pt sponge as

catalyst)

⇒ HNO3 industry

•1909 Ostward (German) received Nobel Prize

for studies of reaction rate over catalysts

•1912 Paul Sabatier (French) received Nobel Prize

for studies of catalytic hydrogenation of organic

compounds

•1915 Haber Process

N2 + 3 H2 → 2 NH3 (Fe catalyst)

•1919 Fritz Haber (German) received Nobel Prize

•1920 Sabatier published the 1st book on catalysis

•1923 Methanol synthesis

CO + 2 H2 → CH3OH (Cr2O3-ZnO catalyst)

•1930 Fischer-Tropsch Process

CO + H2 → (CH)n (Fe catalyst)

• 1932 Langmuir (USA) received Nobel Prize

For surface chemistry and Langmuir isotherm

• 1936 Modern era in catalysis

Catalytic cracking of petroleum (acid treated clays as catalyst)

BET surface area

Deuterium discovery ⇒ isotope research

• 1963 Ziegler (German) & Natt (Italian)received Nobel Prize for stereoregulated

polymerization catalyst

Three Classes of Catalysts

• Heterogeneous- The catalyst and the reactants are in different phases

• Homogeneous- The catalyst and the reactants are in the same phase

• Biological - Enzymes

Effect of Catalyst on Reaction Profile and Activation Energy

Reaction profiles for theuncatalyzed and catalyzed decomposition of ozone

⇒ Homogeneous Catalysis

Homogeneous CatalysisProduction of acetic acid

1916 acetylene→acetaldehyde→acetic acid1950-1960 oxidation of n-butane or naphtha1955 homogeneous methanol carbonylation use

Ni catalyst by BASF1960 iodide-promoted CO catalyst under 2300C

600atm yield 90%1970 Monsanto synthesis use Rh complex

(180-2200C 30-40atm) yield 99%1980 Celanese and Daicel improve Monsanto

process adding LiI or NaI1996 use Ir-based process improved Celanese process1997 direct oxidation of ethylene by Denko

Production of acetic acid

Methanol carbonylation- Rh catalyzed methanol carbonylation

CH3OH + CORh complex

CH3COOH180-2200C30-40atm

r.d.s Rate ∝ [cat.][CH3I]

14-15wt.% of H2O is required

Enzyme Catalysis

• Enzymes are high-molecular-mass proteins that usually catalyze one specific reaction – or a set of quite similar reactions – but no others.

• Extremely high selectivity• The reactant substance (S), called the substrate,

attaches itself to an area on the enzyme (E) called the active site, to form an enzyme-substrate complex (ES).

• The rates of enzyme-catalyzed reactions are influenced by factors such as concentration of the substrate, concentration of the enzyme, acidity of the medium, and the temperature.

“Induced-fit” Model of Enzyme Action

“Lock and key” Model by Emil Fischer in 1894

Effect of Substrate Concentrationon Rate: [Enzyme] = Constant

Effect of Enzyme Concentrationon Rate: [Substrate] = Constant

Enzyme Activity as a Functionof Temperature

Heterogeneous Catalysis• Many reactions are catalyzed by the surfaces of

appropriate solids.

• Steps in heterogeneous catalytic reactions1. Diffusion to the surface2. Adsorption of reactants3. Surface diffusion of reactants4. Surface reaction5. Surface diffusion of products6. Desorption of products7. Diffusion away from the surface

• Heterogeneous catalysis requires balance of adsorption, reaction, and desorption

Catalyst strongly adsorbing ––> no rxn.Catalyst weakly adsorbing ––> no rxn.

A Surface-Catalyzed Reaction

Nanostructured Materials ( <100 nm)

•Nanostructures represent the transition from atom to solid.• It is essential to obtain particles or pores with uniform diameters and shapes and, for the purpose of particular applications, to arrange and embed them in a superstructure.•Size quantization effects, high number of surface atoms, and special surface states.•Special optical, electronic, magnetic, and chemical properties•Good applications in the areas of signal transmission, data and energy storage, as well as catalysis.

Catalytic Reaction Steps

Adsorption

CO

O2

Surfacediffusion

Precursor

Surfacereaction

Desorption

2CO

Ni,PtNi, Co, Pt metals

RhPt metalsPtPt metals

PtAu, Pt metals

Ag

AgoxidationPtGroup Ⅷdehydrogenation

PtPt, Ir, Pd, Auskeletal isomerization of (HC)n

Group Ⅷhydrogenation

PdPt metals

double bond shift

Group Ⅷhydrogenolysis

W, Ptmost trans. metalsH-D exchange

High activityCatalystRxn’s catalyzed by Metals

Ru, Rh, PdOs, Ir, Pt

CH2=CH2 CH2 CH2

O+O2

CH3OH HCHOO2+

CO CO2O2+

Ostwald process(i)

NO CO+2 2 CO2+2N2

CH4+ H2O CO+ H2

+ 6454 + O2 H2ONONH3850oC

CatalystRxnCu2O or multimetallic oxidee.g. Bi2O3-MoO3

Transition Metal oxide catalysts

C3H6 CH2 CH CN +O2, NH3

H2OComplex metal molybdatesor multimetallic oxidee.g. CdMoO4,

M8ⅡFeⅢBiⅢ(MoO4)12O12

Co2+, Ni2+

One-step ammoxidationto acrylonitrile

butane butadiene

Oxidativedehydrogenation

C4H8 + O2 C4H6 + H2O12

∆H < 0exo

H2+C4H6C4H8dehydrogenation ∆H > 0

endo

Ferrite spinelse.g. MnFe2O4, Zn(Cr2-xFex)O4

“metal” catalyst, high temp. easily coking

Propylene → acrolein + acrylic acid

CatalystRxn

Naphthalene or o-xylene + air→ phthalic anhydride

Supported V2O5

n-butane → maleic anhydride (VO)2P2O7

Butene (or benzene) + air→ maleic anhydride

(VO)2P2O7 (V2O4/MoO3)

SO2 O2 SO3 H2SO412

+ V2O5 + K2SO4 /SiO2

Transition Metal oxide catalysts (continue)

CH3OH lean – Fe2O3-MoO3CH3OH rich – Ag

Solid acid catalysts

(i) alumina & acid-treated clays(ii) alumino-silicate (incorporation of alumina in silica)

silica-alumina(iii) protonated zeolites – behave as highly acidic solutions

amorphous

crystalline

shape selectivityacid amount α no. of Alacid strength α 1 / no. of Al

(iv) super acids

TiO2ZrO2Fe2O3

H2SSO4

-2

SO2

+ calcination

H0-14.5-16.0-12.9

Acid-Catalyzed Rxn’s

Isomerization (alkene double-bond isomerization;trans, cis-isomerization)

Alcohol dehydrationPolymerizationCrackingSkeletal isomerizationAlkylation

Acylation

AcidStrength

increases

e.g.

Disproportation

CH3

+ CH3OH + +

CH3

CH3

CH3

CH3

CH3

CH3

+CH3 C

O

O CH3

CH3 C

O

Cl

C CH3

O

CH3 CH3

CH3

CH3

CH3

CH3

CH3

+ ++2

Solid basic catalysts – less used, and less developed

MgO (/Li2O), CaOK/Al2O3KNH2/Al2O3

M-zeolites (M: Li < Na <K < Rb< Cs specific activity )

Base-Catalyzed Rxn’s

dehydrogenation

aldol condersation

Side-chain alkylation with methanol

CH3CH2CH3

OH

CH3CH2CH3

O

CH3CH CH2

+

+ H2O

H2

CH3CH2CH3

OCH3CCH2C

O OH

CH3

CH3

CH3CCH

O

C

CH3

CH3

H2O-

+ H2OCH3OH+

CH3 CH2CH3

CH2CN CH3OH+ CHCN

CH3

H2O+623K

acid-catalyzed

base-catalyzed

Nanotechnology of Catalysis

• Catalysts are perhaps the first industrial nanotechnology

• 2-10 nm particles (sometimes larger) on high surface area support (Al2O3, SiO2)

Automotive catalyst:nm Pt on γ-Al2O3

Catalyst Particles

• Catalytic reactions occur on catalyst surfaces

• Small particles maximize surface area- optimize use of catalysts

(more metal atoms at surface)

• Catalyst dispersionfraction of catalyst atomsat surface (10-40%)

O2

O OOOOC

OC

2 CO

2 CO 2

Turn-over

Reactive site

Catalyst TurnoverTurnover rate [=] s–1: number of reaction cycles completed at a catalyst site per second

車輛所排放的廢氣是造成空氣污染的最大來源之一，一般引擎所排放的廢氣主要組成為：

carbon monoxide (CO, 0.5 vol.%)unburned hydrocarbons (HC, 350 vppm)nitrogen oxides (NOx, 900 vppm)hydrogen (H2, 0.17 vol.%)water (H2O, 10 vol.%)carbon dioxide (CO2, 10 vol.%)oxygen (O2, 0.5 vol.%)其中對環境危害最嚴重的是CO，NOx，及HC。

Automotive Emission Control

Automotive Emission Control

• Largest use of Pt, Pd and Rh industrially

• Example of typical heterogeneous catalytic reaction

• Three-way catalyst: Pt/Pd/Rh on CeO2

Pt/Pd: CO + 1/2 O2 ––> CO2

Pt/Pd: HC + O2 ––> CO2 + H2O

Rh: NOx + HC(CO) ––> N2 + CO2 + H2O

The Catalytic ConverterThe catalytic converter consists of Rh, Pt and Pd

particles on an Al2O3/CeO2 wash-coat deposited on a

monolith of cordierite

Three Way Converter

OxygensensorEngine

Catalyst

AcceleratorAir

Fuel

Exhaust

Computer

Pt/Pd/RhCeria washcoat

A/F ratio

14.914.614.3

0

100

Conv. %CO

NOx

HC

stoic

Catalyst Support Effects

• Note cyclic operation of catalytic converterFuel lean: CO, HC oxidationFuel rich: NOx reduction

• Yet oxidation and reduction continue even when the A/F mixture favors the opposite reaction!

• How does this occur?

• CeO2 acts as an oxygen storage medium

Fuel rich: Oc + Ce3+ ––> Ce4+ (i.e. CeO2)

Fuel lean: CeO2 ––> Ce3+ + O

Nanoscale Effects in Catalysis

• Are catalyst particles simply small versions of the catalyst material?

• Does the nanoscale influence catalytic properties beyond simply presenting more surface atoms?

• What possibilities exist for nanoscale modification of catalyst behavior?

1. Modification of electronic structure2. Interaction of different structure surfaces3. Spill-over effects/other support interactions4. Variation in fluid phase transport properties

Fuel cells

• Liquid electrolyte : AFC, PAFC, MCFCsolid electrolyte: PEMFC, SOFC

• Low temperature: AFC, PAFC, PEMFChigh temperature: MCFC, SOFC

Fuel cells

Fuel cells

Fuel cells• Concept of solid oxide fuel cell (SOFC)

Fuel cells• Concept of proton-exchange membrane fuel cell PEMFC

The catalysts for fuel cells

• Electrode catalyst supports:@ AFC: carbon, Ni- or Ag-based @ PAFC: carbon@ MCFC: Ni-based cement@ SOFC: Ni-YSZ cement, LSM/YSZ@ PEMFC: carbon

• Fuel cells with non-hydrogen fuel@ direct methanol FC: Pt-Ru/carbon, Pd-Ru/carbon electrode catalysts

@ CH4, gasoline as fuels: adding component of oxidation catalyst into anode

Figure 2. (a) Cyclic voltammograms of carbon-supported Pt catalyst samples recorded in 0.1 M HClO4 solution; T= 20 °C, scan rate 50 mV/s; currents are normalized to the measured Pt surface area (Hupd charge after double layer correction); HRTEM images of a carbon-supported Pt nanoparticle (b), and the nanostructured Pt film supported on organic whiskers (c).

J. AM. CHEM. SOC. 127, (2005) 6821

Catalyst Size Effect- I

• EXAFS of Pt/C and Pt-alloy/C catalysts[S. Mukerjee, J. McBreen, J. Electrochem. Soc. 146 (1999) 600.]

Change in d-band density

particle size / nm

2 4 10

Effect of change in potential of 0-0.54 V

0

0.22

Pt/C

Pt d-band density

Pt-Pt bond distance / nm

2.66 2.78

Pt-alloy effects

Pt/Ni/C

Pt/Co/CPt/Fe/C

Pt/Cr/C

• Pt/Cr/C optimal for O2 redn. due to optimal d-band vacancy

Active sites on edge

Active sites on terrace

TOF = (AR)/(FE)Atomic rate

Fraction expose

demanding

facile

Catalyst Size Effect- II

structure-insensitive

structure-sensitive

Reaction on NanocatalystsH2/O2 reaction at 1000 K

(nonflammable mixture in Ar)

H2 + 1/2 O2 ––> H2O130 nm Pt/CeO2 fresh and after 10 min of reaction

[S. Johansson, K. Wong, V.P. Zhdanov, B. Kasemo, J. Vac. Sci. Tech. A 17 (1999) 297.]

Equilibrium Particle Shape

Reaction alters particle shape!

• Polycrystalline particles become crystalline

• Large particles disintegrate to faceted crystals

500 nm Pt/CeO2 (a) fresh and (b) after 10 min of reaction

Influence of Surface Reaction

• Role of oxygen as reactant- Oxygen adsorption weakens Pt-Pt bonds- Pt (in oxide form) becomes more mobile- Effects not seen for H2, H2O

• Energy transfer from reaction- Adsorption highly exothermic (2.5 eV/t.o.)- High reaction rates (t.o. ˜ 103!)

• Local temperature increase

Angew. Chem. Int. Ed. Vol. 41, pp. 688-714 (2002)

Nano-porous materials

Development of Zeolites

•1950sLinde company; Synthetic A-type zeolite for separation of

normal and branched paraffins•1960s

X and Y-type zeolites for catalytic cracking•1968

First use of “Shape Selectivity” properties of zeolites in selective hydrocracking on erionite•In the past 40 years

Zeolites are used in refining and petrochemicals worldwide.⇒ Many synthetic zeolites are prepared.Many synthetic zeolites are prepared.•1998

160 x 103 tons in catalysis applications

Shape-Selectivity:Catalytic reactions in

Molecular Sieves

Polymerization in Confined Space• Adsorption of Monomer in Vapor Phase• Conducting Polymerization• Control of Polymer Morphology and Physical

Properties• Molecular blending of different polymers

Extrusion polymerization: Catalyzed synthesis of crystalline linear polyethylene nanofibers within a mesoporous silica

Science; 285 (1999) 2113.

Modify Meso-Pore Properties By:

• Direct Synthesis — Changes Pore Diameter by Change in Surfactant Chain

Length — Changes Pore Diameter by Addition of Solubilization Agents — Changes Reactivity by Co-precipitation with Functional

Silane • Post Functionalization

— Silylation Changes Pore Diameter and Sorption Properties — Changes Reactivity by Adding Reactive Species

Si-OH

Si-OH

Si-OH

H3COSiH3CO

H3CO

SHO

O

OSi SH

H2O2

O

O

OSi

SOH

O

O

Grafting of Sulphonic Acid Groups on Nano-porous Materials

MCM-SO3H

Summary

• Catalysts are an existing nanotechnology

• Nanotechnological aspects of catalysis only just beginning to be understood

• More effects to explore- Modification of electronic structure- Interaction of facets- Interaction with support (spillover effects)- Mass transport resistances- Confined space reactions and catalysis