Synthesis of γ-Valerolactone by Hydrogenation of Biomass-derivedLevulinic Acid over Ru/C Catalyst

Zhi-pei Yan,† Lu Lin,*,† and Shijie Liu*,‡

State Key Laboratory of Pulp and Paper Engineering, South China UniVersity of Technology,Guangzhou, 510640, Guangdong ProVince, China and Department of Paper and Bioprocess Engineering,

State UniVersity of New York - College of EnVironmental Science and Forestry, 1 Forestry DriVe,Syracuse, New York 13210, USA

ReceiVed March 24, 2009. ReVised Manuscript ReceiVed June 17, 2009

Ru/C catalyst was used in hydrogenation of levulinic acid to produce γ-valerolactone. The conversion rateand the selectivity of levulinic acid to γ-valerolactone with Ru/C as catalyst were higher than those with Pd/C,Raney nickel, and Urushibara nickel. The optimum preparation conditions of γ-valerolactone by hydrogenationof levulinic acid catalyzed by Ru/C were as follows: temperature at 130 °C, hydrogen pressure at 1.2 MPa,dosage of catalyst at 5.0% (based on the mass fraction of levulinic acid), the solvent being methanol, and areaction time of 160 min. The conversion rate of levulinic acid to γ-valerolactone was found to be 92%, andthe selectivity of γ-valerolactone was 99%. The surface structure variations of the fresh and used catalystswere characterized by XRD and XPS. Furthermore, the reaction pathway for the hydrogenation of levulinicacid was proposed.

1. Introduction

Fossil resources on the background of an increasing worldpopulation and their limited supply will run short in the future.As a result, fossil resource prices will increase drastically dueto more difficult access and increased effort in productionaccompanied by stronger economic dependencies. However,biobased resources are renewable and CO2 neutral in contrastwith fossil fuels. The molecules extracted from biobasedresources already contain functional groups so that the synthesisof chemicals generally requires a lower number of steps thanfrom alkanes. In addition, biobased products may have uniqueproperties compared to hydrocarbon-derived products, forinstance, biodegradability and biocompatibility. Furthermore,products obtained from biomass can fetch a higher added valuebecause of the “natural” or “bio” label. The Biomass Programof the US Department of Energy1 and the Implementation ActionPlan 2006 of SUSCHEM organization in Europe2 promote theincreasing use of renewable biomass for energy and chemicalproduction. On a long-term basis, biomass as the only carboncarrier containing renewable primary energy has to be utilizedas a feedstock for energy and for the chemical industry.3,4 Inparticular, the class of carbohydrates possess a remarkablepotential to act as a future resource. Nature produces the vastamount of 170 billion tons of biomass per year by photosyn-thesis, 75% of which can be assigned to the class of carbohy-drates. Surprisingly, only 3-4% of these compounds are used

by mankind in food and nonfood sectors.5 Thus, much attentionshould be given to increasing the use of biomass for energy,chemicals, and material supply.

Levulinic acid (LA), 4-oxo-pentanoic acid, results fromsubsequent hydrolysis of hydroxymethylfurfural from biomass.It is relatively stable toward further chemical reaction athydrolysis conditions. Processes have been developed to produceit from wood, cellulose, starch, or glucose.6-10 The active groupsof levulinic acid are keto and carboxyl groups. Substitution oflevulinic acid for a portion of the acetyl groups in vinyl acetate-containing resins and cellulose acetate yields materials ofincreased strength. R-Angelica lactone, one of the simplestproducts to be made from levulinic acid, can be converted to aseries of pseudolevulinic acid derivatives and provides a meansof obtaining 3-chlorolevulinic acid. It is convertible to bothR-angelica lactone and γ-valerolactone. The three lactones anddimethylpyrrolidone derived from levulinic acid are goodsolvents.11 The exceptional reactivity of levulinic acid and itslactones coupled with its raw material source would seem toprovide an ideal set of conditions for the use of levulinic acidas a basic chemical raw material.

Hydrogenation of levulinic acid, which can produce γ-vale-rolactone, a potentially useful polyester monomer (as hydroxy-valeric acid); 1,4-pentanediol, also of value in polyesterproduction; methyltetrahydrofuran, a valuable solvent or agasoline blending component; and diphenolic acid with potential

* To whom correspondence should be addressed. E-mail: lclulin@scut.edu.cn (L.L.), sliu@esf.edu (S.L.).

† South China University of Technology.‡ State University of New York.(1) US Department of Energy. Energy Efficiency and Renewable Energy,

Biomass Program; http://www.eere.energy.gov/biomass/ (Accessed June2009).

(2) SusChem. http://www.suschem.org/media.php?mId)5189.(3) Belgiorno, V.; De Feo, G.; Delia Rocca, C.; Napoli, R. M. A. Waste

Manag.(Amsterdam, Netherlands). 2003, 23 (1), 1–15.(4) Kamm, B.; Kamm, M. Chem. Biochem. Eng. Q. 2004, 18 (1), 1–6.

(5) Roper, H. Starch/Starke. 2002, 54, 89–99.(6) Chang, C.; Cen, P. L.; Ma, X. J. Bioresour. Technol. 2007, 98, 1448–

1453.(7) Schraufnagel, R. A.; Rase, H. F. Ind. Eng. Chem., Prod. Res. DeV.

1975, 14 (1), 40–44.(8) Stephen W. Lignocellulose degradation to furfural and leVulinic acid;

US Patent No. 4,897,497; 1990-01-30.(9) Stephen W. Production of leVulinic acid from carbohydate-containing

materials; US Patent No. 5,608,105; 1997-3-4.(10) Cha, J. Y.; Hanna, M. A. Ind. Crops Prod. 2002, 16, 109–118.(11) Leonard, R. H. Levwlinic Acid as a Basic Chemical Raw Material.

Newport Industries, Inc., Pensacola, Fla. 1956, 48 (8), 1331–1341.

Energy & Fuels 2009, 23, 3853–3858 3853

10.1021/ef900259h CCC: $40.75 2009 American Chemical SocietyPublished on Web 07/08/2009

for use in polycarbonate production.12 The present paper focusesexclusively on the catalytic conversion of biomass-derivedlevulinic acid to γ-valerolactone by Ru/C catalyst. We proposethat γ-valerolactone (GVL), a naturally occurring chemical infruits and a frequently used food additive, exhibits the mostimportant characteristics of an ideal sustainable liquid, whichcould be used for the production of both energy and carbon-based consumer products. GVL is renewable, easy and safe tostore and move globally in large quantities, has low meltingtemperature (-31 °C), high boiling point (207 °C) and opencup flashing temperature (96 °C), and a definitive but acceptablesmell for easy recognition of leaks and spills.13

The conversion of LA to GVL has been investigated byseveral groups. Schutte Thomas14 hydrogenated LA using aplatinum oxide catalyst to give GVL with an yield of 87%. LAwas hydrogenated to GVL in the neat liquid phase with a Raneynickel catalyst with an yield of 94%.15,16 Changing to acopper-chromite catalyst produced a complex mixture of GVL,1,4-pentanediol, and methyltetrahydrofuran. Rhenium catalysts[Re black, Re(IV) oxide hydrate] for hydrogenation of LA toGVL have also been described.17 More recent studies haveexamined the homogeneous catalysis of the hydrogenation steps.Both ruthenium and rhodium complexes catalyze hydrogenationof LA at low temperature (60 °C) in aqueous solutions.18,19 GVLwas also produced from LA with a yield of 85-100% usingruthenium iodocarbonyl complexes.20 Ruthenium triphenylphosphine complexes gave a conversion of 99% and an yieldof 86% on GVL in toluene solution.21

The objective of this study was to assess the applicability ofRu/C catalyst in the hydrogenation of LA to GVL, to comparethe activity and selectivity of Ru/C catalyst with Pd/C, Raneynickel, and Urushibara nickel. We decided to examine thereaction conditions for GVL production via hydrogenation ofLA catalyzed by Ru/C and the reaction kinetics of LAhydrogenation.

2. Experimental Section

2.1. Catalytic Reaction Procedure. LA hydrogenation wasperformed in a three-phase 1000 mL steel autoclave. The hydro-genation experiments at elevated pressure were performed in anautoclave made by Switzerland Buchi. A 300 mL portion of a 5wt % solution of LA in methanol with catalyst was introduced intothe autoclave. The system was flushed with hydrogen and thehydrogen pressure was adjusted to the desired value. The systemwas then heated to the desired temperature.

Unless stated otherwise, the following conditions were applied:a temperature of 130 °C and hydrogen pressure at 1.2 MPa. The

catalyst was 5% Ru/C with a dosage of 5.0% (based on the massfraction of LA), and the solvent was methanol. The reaction timewas 160 min. The experiments were repeated twice, then averagedand discussed (the standard deviation was less than 1%).

2.2. Sample Analysis. Samples taken during the reaction wereanalyzed with a GC using an Agilent 6820 (G1176A) gaschromatograph equipped with an HP Innowax polyethylene glycolcapillary column with dimensions of 30 m × 250 µm × 0.25 µmand a flame ionization detector (FID) operating at 250 °C. Thecarrier gas was helium with a flow rate of 1.0 mL/min. Thefollowing temperature program was used in the analysis: 60 °C (1min) - 10 °C/min - 230 °C (5 min). The sample analysis wasconfirmed by a gas chromatograph-mass spectrometer technique(GC-MS). Few samples obtained at different reaction conditionswere analyzed with a gas chromatograph Agilent 6890-5975 GC-MS instrument, equipped with an HP Innowax polyethylene glycolcapillary column of 30.0 m length, 0.25 mm of internal diameter,and a film thickness of 0.15 µm. A carrier gas (helium) flow was1 mL/min, and the following temperature program was used: 60°C (1 min) - 10 °C/min - 230 °C (5 min). The injector temperaturewas 250 °C, and the mass spectrometer used an electron impact(EI) ionization mode with 70 eV of electron energy.

2.3. Catalyst Characterization. The fresh Ru/C was character-ized directly. After reaction, the Ru/C was filtered and washed withcold deionized water. Then it was dried at 55 °C and characterized.

X-ray diffraction (XRD) measurements were performed on aRigaku powder diffractometer (Rigaku, Japan) with Cu KR radia-tion. The tube voltage was 45 kV, and the current was 40 mA. TheXRD diffraction patterns were taken over 2 h in a range of 10-90°at a scan speed of 2°/min.

The X-ray photoelectron spectroscopy (XPS) analysis wasperformed on a Kratos Axis Ultra system with 0.1 eV per step fordetail scan, and the binding energies for each spectrum werecalibrated with a C1s spectrum of 284.6 eV. The core levels of Ru3p and C1s species were recorded and their relative intensitiesdetermined.

3. Results and Discussion

3.1. Synthesis of GVL from LA over Ru/C. Results fromthe experiment on the hydrogenation of LA indicated that nohydrogenation reaction occurred in the absence of the catalyst.Thus, there was no noncatalytic reaction taking place. Therewas little byproduct generated during the conversion of LA toGVL. Therefore, the catalytic activity could be expressed byhydrogenation rate defined as the amount of GVL generatedper minute and per gram of catalyst, at constant reaction timeand dosage of catalyst, which is in proportion with theconversion of LA and the selectivity to GVL.

Initial screening for the hydrogenation of LA involved a seriesof catalysts contains 5% Ru/C, 5% Pd/C, Raney nickel, andUrushibara nickel. The catalytic activity of the catalysts is shownin Figure 1. The hydrogenation rate of 5% Ru/C is higher thanthe others at similar reaction conditions. Hence, Ru/C wasclearly the most suitable catalyst chosen.

Ruthenium is the most active catalyst for hydrogenation ofaliphatic carbonyl compounds.22 The surface area, pore size,particle size distribution, metal dispersion, crystallinity, com-position of the support, reducibility of the precursors, SMSI,hydrogen spillover, traces of elements with modification effects,etc., are factors governing the performance of the catalysts.23

Furthermore, from the results of catalyst characterization, onecan stipulate that the reason for higher catalytic activity of Ru/Cis a combination of the small particle size and the high surfacemetal dispersion degree.

(12) Bozell, J.; Moens, L.; Elliott, D. C.; Wang, Y.; Neuenscwander,G. G.; Fitzpatrick, S. W.; Bilski, R. J.; Jarnefeld, J. L.; Production oflevulinic acid and use as a platform chemical for derived products. Resourc.ConserV. Recycl. 2000, 28, 227-239.

(13) Istvan, T.; Horvath, H. M.; Viktoria, F.; Laszlo, B.; Laszlo, T. M.Green Chem. 2008, 10, 238–242.

(14) Schutte, H. A,; Thomas, R. W. J. Am. Chem. Soc. 1930, 52, 3010–3012.

(15) Christian, R. V., Jr.; Brown, H. D.; Hixon, R. M. J. Am. Chem.Soc. 1947, 69, 1961–1963.

(16) Kyrides, L. P.; Groves, W.; Craver, J. K. Process for the productionof lactones; US Patent No. 2,368,366; 1945-01-30.

(17) Broadbent, H. S.; Campbell, G. C.; Bartley, W. J.; Johnson, J. H.J. Org. Chem. 1959, 24, 1847–1854.

(18) Jou, F.; Tuth, Z.; Beck, M. T. Inorg. Chim. Acta, 1977, 25, L61-62.

(19) Jou, F.; Somsak, L.; Beck, M. T. J. Mol. Catal. 1984, 24, 71–75.(20) Bracca, G.; Raspolli-Galletti, A. M.; Sbrana, G. J. Organomet.

Chem. 1991, 417, 41–49.(21) Osakada, K.; Ikariya, T.; Yoshikawa, S. J. Organomet. Chem. 1982,

231, 79–90.

(22) Kluson, P.; Cerveny, L. Appl. Catal., A 1995, 128, 13–31.(23) Du, Y.; Chen, H. L.; Chen, R. Z.; Xu, N. P. Appl. Catal., A 2004,

277, 259–264.

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A kinetic study is essential for the analysis of the productionefficiency. The reaction time was varied from 0 to 240 min, asshown in Figure 2. Figure 2 shows that with the extension oftime, the conversion of LA and the selectivity of GVL grewvery fast at the beginning of the reaction. After 80 min ofreaction, the pace of progress became slower. When reactiontime exceeded 160 min, the pace of progress reached a plateau.Thus, one can conclude that the most effective reaction timefor catalytic hydrogenation of LA to GVL is 160 min.

The effect of hydrogen partial pressure in the pressure rangeof 0.3-1.5 MPa on the rate of hydrogenation is shown inFigures 3 and 4. Figure 3 shows that the hydrogenation rateincreases with increasing hydrogen partial pressure. At lowhydrogen pressure, the concentration of hydrogen dissolved inmethanol solution follows with Henry’s law.24 Hence, theincrease of hydrogen concentration with enhancement of thehydrogen pressure leads to an clear increase of reaction rate. Inaddition, as Figure 4 shows, with increasing hydrogen pressure,the conversion of LA continues to grow and the selectivity ofGVL increased first, then decreased after the pressure reached1.2 MPa. Since the dehydration of γ-hydroxyvaleric acid togenerate GVL is endothermic, increase in hydrogen pressurewas less favorable to the conversion of LA to GVL. With theaugumentation of hydrogen pressure, the reaction rate wasdominated by the increase of the concentration of hydrogendissolved in methanol solution. After the pressure reached 1.2MPa, adverse influence of increased pressure on the chemicalequilibrium of reactions becames significant. When all factorswere taken into consideration, the optimum hydrogen partialpressure chosen is 1.2 MPa.

The effects of temperature on reaction rate were shown inFigure 5. The curves are similar to those in Figure 4. Elevated

temperature promoted the diffusion of hydrogen in methanolsolution. On the other hand, the hydrogenation is reversibleexothermic process. Elevation of temperature is unfavorable forthe extent of reaction. The benign temperature exerted is130 °C.

The system was checked for external transport limitation byvarying the dosage of the catalyst and the agitation speed. Thevariation in reaction rate over the dosage of the catalyst is shownin Figure 6. One can observe from Figure 6 that the conversionof LA increased rapidly as the dosage of Ru/C increased from1 to 3%. The increase in the conversion of LA slowed to a

(24) College of Industry of Forest Products in Nanjing. Handbook ofChemical Industry of Forest Products; China Forestry Press: Beijing, China,1980.

Figure 1. The effect of catalysts on the hydrogenation of LA (the whitebar is the conversion of LA in %, the black bar is the selectivity ofGVL in %).

Figure 2. The effect of the reaction time on the hydrogenation of LA(the open symbols are for conversion of LA in %, the filled squaresrepresent the selectivity of GVL in %).

Figure 3. The effect of system pressure on the hydrogenation of LA(the open circles represent the conversion of LA in %, the filled squaresrepresent the selectivity of GVL in %).

Figure 4. The effect of system pressure on the rate of hydrogenationof LA (the filled squares represent 1.5 MPa system pressure, the opencircles are for 1.2 MPa system pressure, the upward triangles are for0.9 MPa system pressure, the filled downward triangles are for 0.6MPa system pressure, and the open diamonds are for 0.3 MPa systempressure).

Figure 5. The effect of temperature on the hydrogenation of LA (theopen circles are for the conversion of LA in %, the filled squares arefor the selectivity of GVL in %).

γ-Valerolactone from LeVulinic Acid Energy & Fuels, Vol. 23, 2009 3855

trickle with further increase in the dosage of Ru/C. The variationin selectivity over the dosage of the catalyst is an ascendingcurve, with its uptrend rate descending at the Ru/C dosage of5%. A possible explanation for this phenomenon is that duringcatalytic reaction active sites of the catalyst undergo changes.Active sites increased as the dosage of Ru/C was increased,which may have promoted the hydrogenation of LA. However,the number of active sites no longer is a limiting factor for thehydrogenation of LA when the dosage of the catalyst increasedto a critical value. The benign dosage of Ru/C was found to be5%.

In solid-catalyzed gas-liquid reactions like hydrogenation,the mass transfer effect can be more important than the reactionitself. Agitation speed, an important process parameter influenc-ing the hydrogenation reaction, was varied from 200 to 1200rpm, and the results of reaction are given in Figure 7. Figure 7shows that the conversion of LA increased slowly and theselectivity to GVL grew rapidly as agitation speed increased

from 200 rpm to 1000 rpm. There is no influence of the agitationspeed (when the agitation speed is equal or greater than 1000rpm) on the activity. These results show that the agitation speedof 1000 rpm is preferable for the best result of reaction.

3.2. Catalyst Characterization and Reuse. The XRD pat-tern of the fresh and used Ru/C is shown in Figure 8. Only twodiffraction peaks at 25.7 and 43.2° are observed in the 2θ rangefrom 10 to 90°, which are the characteristic peaks of activecarbon. The characteristic peaks of Ru did not appear. Thereare two reasons for the missing peaks. First, there is less loadof Ru in the catalyst of Ru/C. Second, particle size of Ru isvery small and the granules dispersion is homogeneous.However, XPS results show that the catalyst consists of Ru, C,Cl, and a small amount of oxygen, and no other elements aredetected by XPS.

Because of the electron binding energy of C1s at closequarters with Ru3d3/2, it exhibited the strongest characteristicpeak of Ru. We adopted the Ru3p diffraction peak to detectthe content changes of Ru in Ru/C. Figure 9 is Ru3p XPS

Figure 6. The effect of catalyst dosage on the hydrogenation of LA(the open circles are for the conversion of LA in %, the filled squaresare for the selectivity of GVL in %).

Figure 7. The effect of agitation speed on the hydrogenation of LA(the open circles represent the conversion of LA in %, the filled squaresare for the selectivity of GVL in %).

Figure 8. XRD pattern of the fresh and used Ru/C catalysts (the blacktrace is fresh, and the blue trace is used).

Figure 9. Ru 3p XPS spectra of fresh and used Ru/C catalysts (theblack trace is fresh, and the blue trace is used).

Figure 10. The effect of Ru/C catalyst reuse times on the hydrogenationof LA (the open circles represent the conversion of LA in %, the filledsquares are for the selectivity of GVL in %).

Figure 11. GC spectra of LA hydrogenation products (the green tracesis 40 min, and the red trace is 100 min).

3856 Energy & Fuels, Vol. 23, 2009 Yan et al.

spectra of the fresh and the used Ru/C. One can oberve thatthere is Ru on the surface of the catalyst, and part of Ru is lostduring the catalysis process. The ratio of the integral area underthe peaks of Ru3p and C1s for fresh and used Ru/C, respectively,are AC:ARu ≈ 37:1 for fresh Ru/C and AC:ARu ≈ 49:1 for usedRu/C. The value of AC:A Ru approaches the ratio of the numberof C atoms to the number of Ru atoms. Hence, it can beconcluded that part of Ru was lost during catalysis process. Thisleading to speculation that the used Ru/C are active but theactivation will be depressed.

The oxygen detected by XPS might be caused by someoxides, such as RuO or RuO2, which is formed during thestorage process. Although Ru is in its metallic form underreducing conditions, it will oxidize when exposed to oxygen.The ratio of the integral area under the peaks of O1s and C1sfor the fresh and the used Ru/C, respectively, are AC:AO ≈ 9.8:1for fresh Ru/C and AC:AO ≈ 10.2:1 for used Ru/C. The valueof AC:AO approaches the ratio of the number of C atoms to thenumber of O atoms. There was a minor change of the numberof O atoms between the fresh and the used Ru/C. Therefore,the oxides do not change during reaction, and they do not haveany real influence over the hydrogenation of LA except for theformation of oxides-deactivated Ru/C. Probably as a result ofthe extremely low concentration, those oxides are not observedwith XRD. The excessive broadening of diffraction peaks couldbe due to the very fine nature of the metal particles.

On the basis of the analysis above, it was conjectured thatthe Ru/C catalyst can be reused. Then, the reuse experimentsof 5 wt % Ru/C catalyst were conducted (Figure 10). The initialhydrogenation rate decreased over 5 wt % Ru/C catalyst in thereuse. It can be seen that the fresh Ru/C catalyst gave 92% LAconversion and 99% GVL selectivity. However, on the twice-used Ru/C, the LA conversion and the GVL selectivity droppedto 61 and 70%, respectively. On the fourth-used Ru/C, the LAconversion and the GVL selectivity remained at about 42 and48%, respectively. It can be concluded that the activity stabilityof Ru/C is not very good, but the catalyst can be reused withsome fresh catalyst added.

3.3. The Reaction Pathway for the Hydrogenation ofLA. During the experimentation, the products of hydrogenationreaction were analyzed by GC-MS, as shown in Figure 11.Products were detected as methyl levulinate, GVL, pseudo-LA,γ-hydroxyvaleric acid, and LA, respectively, based on the

different appearance time of peaks at 9.7, 10.4, 10.9, 11.5, and17.7 min. The methyl levulinate might be the product of theesterification reaction of LA and methanol, but counter-reactionof the esterification reaction will take place with the release ofLA. Pseudo-LA coexists with LA in the reaction solution. Bothof them have a reciprocal transformation.25 The amount ofisomer of LA gradually decreased as the reaction progressed.Hydrogenation of LA first yields γ-hydroxyvaleric acid, which,as the free acid, lactonizes readily to γ-valerolactone (lactoneof γ-hydroxyvaleric acid). With no other products found in themixture, the Ru/C catalyst is found to exhibit high catalyticselectivity.

Under the experimental conditions employed for hydrogena-tion of LA over Ru/C catalyst, a reaction pathway is proposedas summarized in Scheme 1. It is proposed that the first stepduring hydrogenation reaction was chemisorption of hydrogenand LA. Hydrogen was adsorbed on the surface of Ru throughthe formation of hydrogen bonds between hydrogen and Ru. Itis analogous to the coordination compound of hydrogen andRu. LA was adsorbed on the surface of Ru by the combiner ofRu with carbonylic C and O atoms.26 Followed is the divisionof the H diatom. The two atoms of H are transferred separately.20

When the first H was added to LA molecule, an intermediatethat is linked by a σ-bond is formed. The intermediate isstablized by its interaction with Ru. If the intermediate acquiresone more H atom, it then forms γ-hydroxyvaleric and is bondedon the surface of Ru. Then, γ-hydroxyvaleric loses one moleculeof water, rapidly generating GVL.

4. Conclusion

It was shown that γ-valerolactone could be synthesizedthrough hydrogenation of biomass-derived levulinic acid overRu/C catalyst. Results from the reaction processes led to thefollowing conclusion:

GVL can be produced in very high yield from biomass-derived LA. Ru catalyst is particularly active and selective forthis reaction.

(25) Chen, S. Y.; Chen, P. Kinetics of catalytic reaction; ChemicalIndustry Press: Beijing, China, 2007.

(26) Kieboom, A. P. G.; van Rantwiik, F. Hydrogenation and Hydro-genolysis in Synthetic Organic Chemistry; Science Press: Beijing, China,1981.

Scheme 1. Reaction Pathway for the Hydrogenation of LA

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The optimum conditions for preparing GVL by hydrogenationof LA catalyzed by Ru/C were as follows: a temperature of130 °C, a pressure of 1.2 MPa, a dosage of Ru/C catalyst of5.0% (based on the mass fraction of LA), and the solvent beingmethanol. The conversion rate of LA was 92%, and theselectivity of GVL was 99%.

Acknowledgment. The authors are grateful for the financialsupport from Natural Science Foundation of China (50776035,U0733001), Foundation of Scientific Research for Universities

(20070561038) and Initiative Group Research Project (IRT0552)from Ministry of Education of China, National High TechnologyProject (863 project) (2007AA05Z408), and National Key R&DProgram (2007BAD34B01) from the Ministry of Science andTechnology of China.

Note Added after ASAP Publication. Reference 12 wasmodified in the version of this paper published ASAP July 8, 2009;the corrected version published ASAP July 10, 2009.

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