Effect of La on Partial Oxidation of Ethanol to Hydrogen over Ni/Fe Catalysts

CHEM. RES. CHINESE U. 2003. 19(2), 206-210Effect of La on Partial Oxidation of Ethanol to Hydrogenover Ni/Fe CatalystsWANG Wei-ping, WANG Zhi-fei, DING Yan and LU Gong-xuanState Key laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical PhysicsChinese Academy of sciences, Lanzhou 730000, P.R. ChinaReceived Jan. 18, 2002The partial oxidation of ethanol to hydrogen was investigated over Ni/Fe/ La catalysts prepared by theco-precipitation method. The effects of introduction of La promoter and the reaction temperature on thecatalytic performance were studied. It was found that the introduction of La into Ni /Fe catalysts is helpful toincrease the selectivity to hydrogen and the stability of the catalysts. The results of XRD and XPS characterzation show that the structure of the catalyst was changed during the reaction. The existence of LaFeO3species is possibly the main reason of the increase of the catalyst stability.Keywords Ethanol, Ni/Fe/La catalyst, Partial oxidation, Production of hydrogenArticle|D1005-9040(2003)-02-206-05Introductiondrogen from ethanol is promising.Offering significant advantages, which includeAt present, only a limited number of reportsthe absence of pollutant emission and high efficien- have been found in the literature dealing with pro-cy, fuel cells may be an important power of vehi- ducing hydrogen from ethanol, and the work wascles. However, the extensive use of fuel cells is mainly focused on the development of the processeslimited due to the difficulties in H, storage and dis- for ethanol steam-reforming to syngas or hydrogertribution. Producing hydrogen from liquid hydro- rich gasesIn regard of the use of the supportgen fuel and applying it to the fuel cell will be an ed catalysts, copper- and cobalt-based catalystsalternative solution to resolve the problems. have been mainly studied in the steam-reforming ofAmong various liquid fuels, many efforts I-3) have ethanol. However, ethanol partial oxidation to hybeen made to produce hydrogen from methanol by drogen has hardly been studied except for ouring methanol synthesis-based catalysts. Hydro- work. Compared with the process of ethanolgen can be produced by the decomposition of steam-reforming, the process of ethanol partial oxmethanol, the steam-reforming of methanol and idation to hydrogen shows significant advantagesthe partial oxidation of methanol etc.. However, for instance, easily obtained raw material, exothermethanol is mainly produced from the fossil fuel 4, mic reaction does not need the additional heat sup-but its reservation is limited and it causes the envi- ply, easy start-up and all that, and will be a potenronmental pollution. Therefore, ethanol as an al- tial method of producing hydrogenternative raw material is full of promise. The reaIn the previous work, we found Ni/Fe catasons are: (1) the amount of hydrogen produced lysts showed good catalytic properties for ethanolfrom per mole of ethanol is higher than that from partial oxidation to hydrogen under the mild condiper mole of methanol;(2) ethanol is a renewable tions(573 K). However, the stability of this kindmaterial which can be easily obtained from of catalyst is poor, the reason may be that thebiomass; (3) there is no sulfur in ethanol which FeNi phase is partially converted to the (Ni, Fe)usually leads to the poisoning of the Pt electrode of Fe中国煤化工ocess of ethanothe fuel cell (4)there is no CO2 evolution in the oxiCNMHGintroduced promoterprocess of ethanol to hydrogen since CO2 produced LaCLIlis consumed for biomass growth, thus offering a found that the introduction of La promoter signifinearly closed carbon loop. So the production of hy- cantly increased the hydrogen selectivity and theSup数据the973 project of China(G20000264)** To whom correspondence should be addressedWANG Wei207stability of the catalysts 19.20. The present paper 3Characterizationcovers the Xrd and Xps characterization results ofThe x-ray diffraction (XRD) patterns werethe Ni/Fe/La catalysts, which indicate that the recorded on a D/MAX-RB X-ray diffractometerformation of LaFeO3 species may be the main cause with Cu Ka radiation and a Ni filter in the scanningExperimental4/ min at 50kv and 80 mA. The X-ray photoelecI Preparation of the Catalyststron spectroscopy(XPs) measurements were perNi/Fe/La catalysts were prepared by the co- formed at room temperature on a VG ESCALABecipitation method. The catalysts precursors 210 spectrometer with Mg Ka radiation (hvwere prepared by adding an aqueous mixture solu1253. 6eV). If it was necessary, the sample wastion of the metal salts. i. e. Ni(NO,,, ion-sputtered by Ar ions for 0, 30 and 90 min atFe(NO3)3, La(NO3)2, which depended on the indi3kv and 80 ma before the measurement. Thecated catalyst comnt,to a vigorously stirred binding energies are calibrated by the Cis bindingsolution of Na,cO, at room temperature. The re- energy of 285.0 evsulted precipitate was filtered and washed with dis-Results and discussiontilled water until ph was 7, then dried in air at 3831 XRD ResultsK over a night. At last, the co-precipitated cata-There were (Ni, Fe)Fe,O, species and Feni3lyst precursors were calcined in air at 400 C for 3 h alloy species in the Ni/Fe catalysts. However,and crashed to 40-60 mesh. The composition of the introduction of promoter La into the Ni/ Fe catthe catalysts was expressed in the molar ratios of alysts changed the composition of the Ni/Fe catametals Ni, Fe and La(Niso Feso; Nis Feas La4; Nilysts. The xrd patterns of the used Ni/Fe/la catalysts are shown in FiThe phase LaFeo3 was2 Reaction StudyThe partial oxidation reaction of ethanol wasFe)Fe2O3 species and FeNi alloy species, and thefixed-bedreactor(04 mm). Typically, 200 mg of the cata- species increases gradually with the increase of thelyst was used each time and diluted with quartzLa content, while the intensities of (Ni, Fe)Fe, O3And the reaction temperature increased from 473 to823K. The calcined catalysts were reducedby a 10% H, in n, stream (flow rate 30 mL/ min)at573 K for 3 h prior to use. Ethanol was supplied bmeans of n, and O, carriers in a set of jacketed saturator that was maintained by an external temperaUture bath which could ensure that the ethanol flow28/(°)5 mL/min, the total fl35 mL/min. The gas phase effluents were analyzedFig. I XRD patterns of the catalysts after the reactionn two on-line chraphs equipped with that 823 K and n(O,/n(EtOH)=1.mal-conductivity detectors(TCD), a 13X moleculara. NisFesLai: b. Nias ajo; c. Nia Fea Laigsieve and porapak Qand FeNi3 diffraction peaks decrease. The peaks ofHydrocarbons as well as oxygenated productsthe fresh Nias Feas Laa catalyst in the XRD patternwere separated on a porapak T column and ana- having been reduced in a hydrogen stream at 573Klyzed by means of a flame ionization detector and cooled to room temperature in a nitrogen(FID). The catalysts were cooled to room temper中国煤化工 ak compared with theature in a nitrogen stream to prevent them from beCNMHGe Fig 2). That meansing oxidized. The ethanol conversion was definedhe degree of the crystallization of the LaFeO3as the molar ratio of CH OHonsumption 1/ is greatly enhanced during the reaction, which mayLC,H OHed and the hydrogen selectivity was debe caused by the reconstruction of the sample. It isfined as [333359-3H2preduced ]/[1 mol C, H, OHd]. of interest to note that the LaFeOa phase or theother La species phases were not observed in the208CHEM. RES CHINESE UVol. 19fresh Nias FeasLa4 catalyst, which indicates that the contrary, the average particle sizes of (Ni, Fe)La species is highly dispersed or exists as an amor- Fe2O, and FeNis increase graduallous statHowever, the average particle size of FeNi, ofthe Niso Feso catalyst is the largest, which correFeOssponds to the decrease of the catalytic activity at aFe)Fe2O 4ther high temperature. Typically, catalystNisFesla, shehighealyticwhich (Ni, Fe)Fe,O and FeNis have a rather smallparticle size26/(°Table 1 The average particle size of LaFe O3,(Ni, FeFe,0. and FeNi, in Ni/ Fe/ La catalysts calculatedby Scheerer formulaFig 2 XRDrns of Nias Fea La catalystLaFe(Fe)Fe,O FeNiThe average particle sizes of all the phases ofNisFeaslay(usedthe Ni/Fe/La catalysts calculated by means ofNis FesLay(usedNia Fear laig (used)Scherrer formula are shown in Table 1. It can beNiagFeaslag(fresh1413seen that the average particle size of LaFeO, deNisoFeso(used14creases with the increase of the La content, on theFe 0 mina Ni o min832834g36838840842c Fe 90 min(E)(F)Fe 30836838840842Fig 3 XPS of Nizp, Fexp and La, for the Nias Fe s La, and Ni. Fe4 Lais catalysts2 XPS Resultstributable to the oxidized Ni( I ) And consideringFig 3 shows the XPS patterns of Ni, Fe and the XRD results, it is believed that the metal NiLa of catalysts Nigs Fe48 La4 and Nia Fe, La and belongs to the alloy FeNis species and the oxidizedthose having been sputtered by argon ions for difNi(I)is(Ni, Fe)Fe,O3 species. The intensities offerent time. The binding energies of Layd andall the patterns reduced after sputtering, whichmay be caused by the effect of electric charges onFezparz are 835. 90 and 711. 47 eV, respectivelyAccording to the standard XPS data, 835. 90 and中国煤化工, the Xps results were711. 47 ev are assigned to oxidized La and FmaCNMHG multiple(3 times).Itspecies in the Nias Fes La, catalyst, respectivelyan be found that only one binding energy of nizpbefore sputtering. Yet the two Nizpy, binding ener- is shown, at 853. 04 eV, assigned to the metal Ngies indicate the two chemical states of Ni speciesHowever, the peak of Fs dividedOne is 859522*3, which is assigned to metal Ni, peaks, at 710. 37 and 706. 76 eV, respectivelyand the other is 856. 41 eV. which can be atAccording to the standard xps data, the lowerWANG Wei-ping et al.binding energy is assigned to the metal Fe, and the ev with the increase of sputtering times, whichother is attributable to the oxidized Fe( I). Comdicates that the chemical environment around thebined with the XRD results, the metal Ni or Fe be- La atom changed to the reductive ambience. Andngs to alloy FeNis, while the oxidized Ni and Fe the two binding energies of the Nizp of catalystare(Ni Fe)Fe2O3 speciesNia Fe, Lais appeared, according to above analysisIn the case of catalyst Nia Fe, Lais before sput- whichcan be assgned to the metal Ni and oxidizedtering,the similar phenomena were observed. Af- NI( ) respectively. And the surface concentra-ter sputtering, however, the binding energy of tion ratio of the metal and oxidized Ni increasesLa, decreased gradually from 835. 18 to 834. 89 markedly from 0 to 1. 194(Table 2)Table 2 The ratio of atomic concentration calculated from XPs resultsThe ratio of atomicNiagFeaslaNiasFeasl-aNin Feal laigconcentrationsputteringputtering for 60 minMetal Fe/2/Fepe2(Ⅱ)1.204194Metal Niz/N(I)1.480The trend of Fe peaks is similar to that of Ni are higher than that of catalyst Ni/ Fe at 673-823peaks. Combined with the XRD results, the metal K may be that LaFeO3 species stabilizes the activeNi and Fe are assigned to FeNi, that mainly locates species. Catalyst NiAs Feasla, shows a higher H2 seon the surface of the catalysts, while the oxidized lectivity at 523--773 K, which is possibly resultedNi and Fe can be attributed to the complex com- from the small average particle size of (Ni, Fe)pound (Ni, Fe)Fe2O3 that primarily exists in the Fe,O, and FeNis speciesbody of this sample, and LaFeO3 phase dispersesall the catalyst3 The Effect of Reaction Temperature on theCatalvtic ActivitPartial oxidation of ethanol to hydrogen wascarried out in a fixed-bed continuous flow quartzreactor at a feed ratio O, / C,H,OH of 1. 5. It can befound from Fig 4 that the ethanol conversion over473523573623673723773823T/Kcatalyst Nis Feso is obviously higher than that overthe Ni/Fe/ La catalysts in the temperature rangeFig4 Ethanol conversion as function of temperaturefrom 473 to 723K, but decreases when temperaover Ni/Fe/La catalysts and Nise Fe se catalystture is over 723 K. The decrease of the activity ofNi4Fe4La;▲ NisFeisla;◆ Nia Fellas;■ NisoFecatalyst Niso Feso may be caused by the sinter of thecatalyst at a rather high temperature. The ethanolconversion over the Ni/ Fe/La catalysts increaseswith the increase of the reaction temperature. Andcatalyst Nias Fe4 La, shows a higher catalytic activity at a relatively lower temperature(473--573 K)and the highest activity at higher temperatures(723--823K than the other Ni/Fe/La catalysts047352357362367372373823r/Kand among all the catalysts. The ethanol conver-sion reaches 65. 6% at 523 K and increases toFig 5 Hydrogen selectivity as function of temperature22 at 823 K. Hydrogen selectivities of all the niFe/La catalysts increase markedly with the in-中国煤化工 s and nisofesohe as those in Fig 4.crease of reaction temperature in the relatively lowCNMHnalysistemperature range, but increase slowly at a ratherThe stability of catalyst Nis Feas Lao was ehigh temperature( Fig. 5). In the case of catalystamined at 773 K and a feed ratio O2/C2,OH ofNiso Feso, the hydrogen selectivity of it decreases1.5. The results are shown in Fig. 6, in which thewhen the F h*ure is 823 K. The reason of the alternations of activity and selectivity to hydrogenfact that H, selectivities of the Ni/Fe/La catalysts210CHEM. RES CHINESE UVol. 19Under the experimental conditions Fig 6), XRD and XPS characterization show that theethanol conversion kept about 90% during the first structures of the catalysts were changed during the23 h and increased with the time-on-stream, and reaction. The existence of LaFeO3 species is possireached 100% after 63 hoursrogen selectivity bly the main reason of the increase of the catalystfirstly increased slightly then decreased appreciably stabilitywith the time-on-stream, and maintained 70% during the last 40 h. Compared with the stability of Referencescatalyst Nis] Feso, whose hydrogen selectivity de- L 11 Shen W J. Matsumura Y. Phys. Chem. Chen. Physreased quickly during the first 40 h, the stabilities2000,2,1519of the Ni/Fe/ La catalysts were improved obvious-[2 Reits T. L, Ahmed S, Krumpelt M.,. .Mol. CataL. Aly, which is probably due to the existence of [3 wU Gui-Sheng, CHEN Xiao-Ping, REN Jie, Chem. chaLaFeO3 species.nese niversit[4 YANG Hui, LU Tian-Hong, LIU Chang-Peng, et alChem... Chinese Universities, 2000, 21(8),12835 Llorca J, Ramirez P,, Sales I,, Chem. Commun.,2001L6 Rykios X. E,Chem. Commun.2001.851[7 Garcia E. Y, Laborde M. A, Int. Hydrogen Energy1991,16(5),307[8 Marino F. J, Cerrella E. G, Duhalde S, et aL., Int.Hydrogen Energy, 1998, 23(12),1095[9 Freni S, Mondello N., Cavallaro S, et al., React. Kinet.Catal,lett,,2000,71(1),14310」 Galvita vSemin G. L, Sobyanin V. A, ApplFig 6 Conversion of ethanol and selectivity to hydrogenCatal.A,2001,220,123as a function of time-on-stream over Nisa Fese and[11] Marino F, Boveri M., Baronetti G., et al., Int. HydroNiss Feas Lao catalystsgen Energy, 2001, 26,665Experimental condition catalyst 200 mg: T[12 Maggio G, Freni S, Cavallaro S.,, Power Sourn(O2)/n(EtOH)=1.5;p=1.0×105Pa.▲Niso1998,74NisoFeso;■ Nia1Feal.a[13 Freni S.J., Power Sources,2001.14Conclusion14 Vasueva K. Mitra N., Umasanker P, et alThe activities of the different Ni/Fe/La catadrogen Energy, 1996, 21(6),13[15 Luenga C. A, Ciampi G, Cencig M, O, Int. Hydrolysts were investigated at 473--823 K. The experigen Energy,1992,17(9),677mental results indicate that the introduction of proL16 Freni S, Maggio G, Cavallaro S,..Powermoter La can increase obviously the hydrogen se1996lectivity and the stability of the Ni/Fe catalyst[17] loannides T, Power Sources, 2001,92, 17The effect of the reaction temperature on the[18 Wang w. P. Wang Z. F, Ding Y, et aL., Catal. Lett.2002,8(1),6catalytic activity was studied. It has been found [19 Kim D. H, Woo S. I, Lee J. M, et al., Catal. Lettthat the catalytic activity is improved with the tem2000,70,35perature, the ethanol conversion is 96% and the[20] Provendier H, Petit C, Estournes C, et al., Applhydrogen selectivity is 74% at 823 K and a feedCatal.A,1999,180,163molar ratio O,/ C,H Oh of 1. 5. The results of中国煤化工CNMHG