Methanol Steam Reforming Catalysts for Fuel Cell Driven Electric Vehicles

雪Journal o[ Natural Gas Chemistry 12(2003)71-73SCIENCE PRESSMethanol Steam Reforming Catalysts for Fuel CellDriven Electric VehiclesYongfeng Li"，Xinfa Dong;Weiming LinSouth China Uniwversity of Techwlogy, Gtuangzhou 510640. China[Manuscript received Junuary 24, 2003; revised February 18, 2003]A bstract: Cu/ZnAIO catalysts derived from hydrox ycurbonate precursors containing hydrotalcite-likelayered double bhydroxides (LDHs) were studied. The infuence on the performance of the catalysts wasalso studied when the Al in the Cu/ZnAI0 catalyst was partly or completely replacxd by Zr or Ce.Key words: methanol, steam rloning, lyered double hyorxide. fucell } i的。1. Introductionformance over these catalysts in the SRM.2. ExperimentalScientific evidence strongly suggests that therapid build-up of greenhouse gases in the atmosphereA series of Cu/Zn(Zr.Ce)AIO catalysts were pre-is raising the earth's temperature (global warming)pared from hydrotalcite- like layercd double hydrox-and changing the earth's climate with many potentialides (LDHs) precursors. First, the LDHs precrsorsconsequences. Eforts are ciurrently under way to re-were prepared by a specific method [1], then the re-duce the emissions of greenhousc gases such as CO2sulting powders were calcined at 450 C for 6 h andfrom the transportation sector by the use of hydro-used as catalysts for SRM.gen (H2) fueled fuel cells such as polymer electrolyteThe performance of the catalysts was measured inmembrane fuel cells (PEMFC) for powering vehicles.a specific fixed-bed quartz Aow reactor. The catalystsHowever, crrent techuology does not permit the stor-were first rednced in a streain of H2-N2 mixed gasesage of enough H2 to maintain the driving ranges in at 300°C for 3 h. Subsequently. after cooling t reac-which notorists are accustomned just by storing hy-tion temperature of 250 °C, a premixed feed of waterdrogen fucl onboard in high-pressure tanks. So, it isand methanol, with a H2O/McOH molar ratio of 1.3,proposed that hydrogen may be supplied from liquidwas fed into the pre-heater by meaus of a micro- federfuels such as methanol. For the purpose of aford-(iquid flow rate was 2.5 ml/h). The reaction productsing hydrogen to fucl cell electric vehicles (FCEV), thewere scparated with a cooling tank. The gaseous ef-steam reforming of methanol (SRM) is a typical reac-fAuents were determincd on-line by an HP4890D lypetion for generating hydrogen rich gases. Recently wegas chromatograph, and the liquid products were de-have developed a series of Cu/ Zn(Zr .Ce)AIO catalyststermined by a 102G type gas chromatograpb. Thederived from hydroxycarbonate precursors containingcatalytic activity was evaluated from the data col-lydrotalcite-like layered double hydroxides (LDHs). lected from the period between 4 h and 5 h of theThe objcctive of the study is tu investigate the per-on-stream operatiou.”Corresponding author. E mail: yfi021cn.comn.Financial suppurt from Giuangdong Provincial Natural Science Foundation of China (000135), the Doctoral Program Foun-dation of the Ministry of Education (20010561003) and Guangzhou Munici中国煤化工(2001J1-C0211).fYHCNMHG72Yongfeug Li et al/ Jorn of Nialural Ciae Chemnistry: Vol. 12No. I 20033. Results and discussionUsually the reformed gas must pass a Co refinerto remove CO, becausc when feeding hydrogen to a3.1. Performance of the Cu/ ZnAlO catalystsPEMFC, even traces of CO (> 100 ppm) in the hydro.gen rich gas will poison the Pt electrode and lower theThe performance of the Cn/ZnAlO catalysts dc-cell performance dramatically. So, for the purpose ofrivel from LDHs precursor is shown in Table 1. Thetrying 1o minimize the volume of the CO refiner andcalal.ysts displaved good catalytic uctivities at a lowenhancing the wholc cfticiency of the FCEV, the COreaction temperaturc (250 °C). Conmpared with re-content should also be lowcred in the SR.M while keep-latedl results in the litcrature [2 4小this type of Cu-ing a good cratalytie activity. Thus, it is of great sig-based catalysts displayed bigher met hanol coversionnificancc to st udy these catalysts deriving from IIDHsnd better CO2 selectivity (outlct CO molar contentprecursors.reacied 0.11%).Table 1. Performance of CuZn(Zr,Cc)AIO catalysts derived from LDHs precursors in SRMOutlct product cuntenl (%)CatalystX(MeOH)/% 5(H2)/% Y(H2)/% S(C02)/%MeOH H2O H2 CO2CO OtherCu/ZnAIO54.192.149.899.315.318.7 50.0 15.2 0.107 0.596(^an/ZnZrAIO68.586.859.499.59.9715.6 56.3 17.6 0.090 0.448Cn/7nZrO93.281.378.608.01.90 11.6 65.6 20.2 0.224 0.455Cu/ZnCeAIO44.894.342.399.619.3 22.0 44.4 13.6 0.058 0.493Cu/ZnCeO34.494.432.599.226.8 36.6 11.2 0.093 0.556Reaction cundition: 250 "C 0.1 MPa, the mole ratio of H2O to MeOH: 1.3, GHSV=1.757 h 1. no carrier gas.X(A[eOH), S(H2). Y(H2). S(CO2) respectively refer to methanol courvursation, H2 sclctivity, H2 yield and CO2 selectivity.3.2. Efect of substitution of Al by Zr on theore apparent, and the rates of methanol conversioncatalytic performanceand H2 production increased respectively by 39% and29%. On the other hand, CO2 selectivity falls greatly:The methanol decomposition/ refrming reactionresulting in an outlet CO molar content increase by acau be considlered as the reverse of the methanol syn-factor of2. i.e.. to 0.217%.thesis reuct ion over Cu- based catalysts using CO/H2or CO2/1I2 as the feed stocks. It is well kuown in the3.3. Effect of substitution of Al by Ce on theliterature that ratalysts containing copper and ZrO2behave in a bifunctional mnaerr in the mnethanol sSyIn-thesis reaction [5]. A recent repurt U1l tle investiga-CeO2 exhibits good ability in storing and releas-tion of nethaol deconpusition oLl a Cu/ZrO2/SiO2ing oxygell, so it is often used in redox catalysts tocatalyst revcaled the involvement of similar bifuuc-change the valence states o[ the active core ions. Andtional roles of copper and ZrO2 [6]. So, we preparedit is well known that suitable Cn/Cu+ ratio is bene-(wo more catalysts by subtituting Al either partly orficial to the catalytic activity of the SRM reaction. Itcompletely by Zr in the Cu/ZnAIO catalyst. Theirwas reported that Cen _Cu;O2-5 catalysts revealledperformances are given in Table 1.high prformance in the complete oxidation of COFrom a comparison in the performanres betweenand mcthane [7. and rendering CO oxidation at athe Cu/ZnAlO and thc Cu/ZnZrAlO catalysts. it canlower temperature [8]. So we have prepared two ad-be seen that the addition of Zr plays an importantdlitional catalysts by substituting AI either partly orrole in the rates of Inethanol conversion and H2 pro-conupletely by Ce in the Cu/ZnAIO catalyst. Theirduction, with a respective increase of 15% and 10%.perfornances are ilustrated in Table 1.From a furt her comuparisou of the performances be-By comparing the performances of the Cu/ZnAIOtwel the Cu/ZuAlO aud the Cu/ZuZrO calalysts,aurd the Cu/ZnCeAlO catalysts, it can be seen thatit can be seen that when substituting AI cuupletelythe addition of Ce can introve both the H2 selectiv-by Zr in the Cu/ZnAl0 catalyst, this effect becomes中国煤化工ulting in a decreaseYHCNMHGResearch Notes / Journal of Naturul Gas Chermistry Vol. 12 No.1 200373in the onttlet CO molar content to 0.058%. However,Referencesthe addition of Cc lowered the rates of methanol co1-version and H2 production greatly, decreasing by 9%[1] Velu s, Suznuki K. Osaki T. Catalysis Lotters, 1999.and 7% respectively. Moreover, when substituting Al62: 159completely by Ce in the Cu/ ZnAlO catalyst. the rates[2)| Qi A D. Hong X L, Wang Sh D. Mod Chem Indu,of methanol conversion and H2 production decreased2000. 20(7): 37further by 20% and 17% respectively.[3] Liu Y Y, Hayakawa T, Suzuki K, et al. CatalysisCununications, 2001, 2: 1954. Conclusion|4] Chen B. Dong X F, Lin W M. Natur Gas Chem Indu,2000. 25(2): 1Cu/Zn(Zr,Ce)AIO catalysts derived from LDHs[|5] FisherI A. Bell A T. J Catal, 1998, 178: 153precursors revealed good catalytic perfornances inthe SRM reaction at a lower termperature. The addi-[6] Fisher 1 A. Bell A T. J Catal, 1999, 184: 357tion of Zr can enhance the rates of methanol cover-[7] Liu w. Hlytxani-Stcphanopoulos M. J Catal, 1995,sion and H2 production grcatly, and the addition of153: 304Ce can improve both the H2 selectivity and the CO2[图Arias A M, Cataluna R, Conesa J C. Soria J. J Physselectivily.Chem B, 1998, 102: 809中国煤化工MYHCNMHG