Effects of La2O3 contents on the Pd/Ce0.8Zr0.2O2-La2O3 catalysts for methanol decomposition

Available online at www.sciencedirect.comJOURNALOPScienceDirectRARE EARTHISELSEVIERJOURNAL OF RARE EARTHS, VoL 29, No.6, Jun.2011,P. 544www.re-journal.com/en/Effects of La2O3 contents on the Pd/Ceo.gZro:2O2-La2O3 catalysts for methanoldecompositionLI Xue (李雪), ZHANG Lihua (张利作)，ZHANG Chao (张超), ZHAO Ming (赵明), GONG Maochu (龚茂初),CHEN Yaoqiang (陈耀强)Key Laboratory of Green Chemistny & Technology ofMinistry of Education, Colle ofChemisty Sichuan University, Chengdu 61006. China)Roceived 23 Decemnber 2010; revised 18 March 2011Abstract: The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CcO2-ZrO2 promoted with La2Oz were investigated for methanoldecomposition. The measurements of inductively coupled plasma emission spectroscopy (CP), N2 adsorption-desorption (BET), powderX-ray dfaction (XRD), X may photolectron spectroscopy (XPS), temperature programmed reduction (TPR) and oxygen storage capacity(OSC) were used to characterize the properties of catalysts. The catalysts' activities were tested in a fixed bed continuous flow reactor operat-ing under atmospheric presure. The PdCevygZro2O>~-5 wt.%La2O3 catalyst exhibited the best acivity. The reasons for this were twofold: (1)doping ofLa improved efectively textural properties ofCeO2 ZrO2 oxygen storage materials, and (2) Pd/Ce,gZTo2O2-5 wt.%L a2O3 pssessedsuper oxygen storage property and reducibilityt due to the existence of lttice defect oxygen or mobile oxygen, which helped to re oxidize 7erovalent Pd' to a partly oxidized Pd+. By introducing 5 wt.%I a2O3, the specific surface area of the sarmple increased, but declined if furtherincreasing the content ofLa2O3 to 10 wt%.Keywords: methanol decomposition; palladium; CcO2- ZrO>2-La2O3; XPS; catalyst; rare earthsIn order to solve the energy crisis and environmental pol-CeO2 ZrO2 catalysts with different methods and found thatlution problems, methanol is regarded as an altemative fuelcatalysts prepared by co-precipitation method were betterfor automobiles in the future. Recently the decomposition ofthan that by impregnation method because the former pos-methanol to CO and H2 is of concerm. The decomposition ofsessed smaller Pd particles (about 3 nm), and there was anmethanol is an endothermic reaction and can recover theactive state of Pd* (0<8 2), which was advantageous towaste heat from methanol-fuelled vehicles in which the de-methanol decomposition. Moreover, CeO2-ZrO2 supportcomposition gas is fed to the engine. Experimental resultscould enhance the dispersion and stability of palladium par-demonstrate that decomposed methanol could be up to 60%ticles.d. Research by Sun et al!(7 and Yang et al!8] showedmore efficient than gasoline and up to 34% better thanthat addition of La2O3 into CeO2 support increased signifi-un-decomposed methanol. NOx emission will also be greatlycantly the activity of catalysts because lanthanum oxidereduced due to lower combustion temperatureslha. However,promoted greatly the dispersion of active components andbecause of the limited space in the engine fuel compartment thereout increased the number of active centers. Li et al.9and the limited temperature of the exhaust heat, especially atreported that CeO2 and/or La2O3 increased the electron den-cold start, the methanol decomposition catalysts present thesity around Pd, which was owing to the electron donationlow temperature activity and selectivity to CO and H2, whichfrom CeO2 and La2O3 to Pd. Recently, La2O3 was doped onare the stringent problems to be solved. Various metals likeZrO2-Y2O3, Fe2O3, CeO2- ZrOr~Al2O3 and CeO2-ZrO2 re-nickel, copper, iron, platinum and palladium supported onspectively in order to decrease densification and enhanceAl2O3, SiO2, TiO2, Z02, CeO2, active carbon or syntheticthermal stability at operating temperature for the preparationclays were reported to be effective for methanol decomposi-of thermal barrier coating (TBC) material, low-temperaturetion!34]. For Cu-based and Ni-based catalysts, their low tem-CO oxidation, the treatment of exhaust of natural gas en-perature activity and selectivity to CO and H2 are poor, whilegined vehicles (NGVS) and catalytic combustion of toluenePd-based catalyst pssesses the high activity at low tem-by a number of reearhersto i31. Doping La2O3 retarded theperature and high selectivity for methanol decomposition,collapse of mcsoporous structure of catalysts during the cal-exhibits comprehensive application foreground. However,cination at high temperature, kept high specific surface area,the activity of Pd-based catalyst is greatly affected by thesmall pore size and narrow pore distribution, and restrainedsupports. Liu et al.s and Kapoor et al.6o prepared the Pd/the growth of particles of support and calyt!4-16.中国煤化工Foundation item: Projet spported by the Programs Foundation of Ministry of Education oural Science FoundationofChina (20773090, 20803049)YH ;CNMHGCorresponding author: ZHAO Ming (E-mail: zhaoming@scu.cdu.cn; TeL: +86-28 85418451)DOI: 10161/10020721(10)604954LI Xue et al, Effects ofLa2Oz contents on the PdVCexavZrazO-LazO; catalysts for methanol decomposition545Wang et al!I7] have investigated the activity of Pd cata- applicd to optimize the scparation of H2, CO, CH4 and CO2lysts supported on CeO2-ZrO2-La2O3 mixed oxides with dif-as well as CHzOH, CHzOCH3 and HCOOCH3.ferent Ce/Zr molar ratios for methanol decomposition. The13 Catalyst characterizationresults showed that Pd/Ceo 7Zr.1L20.0O.97 catalyst showedthe highest BET surface area, the highest Pd dispersion, theChemical analysis was carried out by ICP (IRIS Advan-strongest metal- support interactin and the best activity fortage System from Thermo Electron), which was performedmethanol decomposition. Nevertheless, they did not investi-for catalysts melted in acid solution to evaluate contents ofgate the optimum content of lanthanum in CeOr ZrO2-La2O3metals in the catalysts.supports. And the efet of lanthanum doping on CeOr-ZrO2The BET surface area and pore size distribution were cal-support and catalytic activity of catalysts for methanol de-culated by nitrogen adsorpotion-desorpotion at -196 °C us-composition is lttle studied.ing a ZXF-6 instrument (Xibei chemical institute, China). ToIn this paper, a series of palladium catalysts promoted withdesorb surface impurities, the samples were degassed for 1 hdifferent contents of lanthanum on CeOx-ZrO>rLa2Oz supportsat 350 °C in vacuum before measurement.were prepared by co-precipitation. N2 adsorption-desorptionPowder X-ray diffraction (XRD) patterns were obtained(BET), powder X-ray diffaction (XRD), X-ray photoelec-on a D/MAX-Ra rotarory diffractometer, using Cu Ka radia-tron spectroscopy (XPS), temperature-programmed reduc-tion (2=0.15406), 50 kV and 180 mA; samples were scannedtion (TPR) and oxygen storage capacity (OSC) were used tofrom 20 equal to 20° up to 90%).characterize the properties of catalysts.The X-ray photoclectron spectroscopy (XPS) experimentswere carried out on a spectrometer (XSAM-800, KRATOS1 ExperimentalCo.) with Mg Ka radiation under UHV. All samples werepretreated in a stream of 5% H-95% N2 at 400 °C for 1 h, and.1 Catalyst preparationcooled to room temperature. The binding energy was deter-mined by reference to the C1s binding energy of 284.8 eV.The Ceo.gZTo2O2-La2O3 samples with different contents ofTemperature-programmed reduction (H2-TPR) experi-La2O3, e.g. 0, 5 wt%, and 10 wt.% were prepared by Co-ments were carried out in a conventional system equippedprecipitation method from the corresponding chemicals:with a thermal conductivity detector (TCD). All samplesCe(NO3);6H2O, ZrOCO3 and La(NO3):6H2O at a nominal(100 mg) were pretreated in a quartz U-tube in a flow ofcomposition. The precursors were mixed in an aqueous solu-pure N2 at 400 °C for 45 min, then cooled. The reduction re-tion respectively, and an appropriate amount of fresh H2O2action was carried out in a flow of 5% H2 in N2 from 50°C towas added. Then the mixed salt solution was added dropwise900 °C with a linear heating rate of 8 °C/min.into a mixed aqueous solution of ammonia and ammo-Oxygen storage capacity (OSC) was estimated as follows.nia-carbonate to reach a pH value of 9.0 while strring. Fi-A certain amount of catalysts were heated in a quartz reactornally the precipitates were filtered, thoroughly washed, dried,in a flow of 40 m/min H2 at 550 °C for 45 min. Then cata-and calcined at 600。C for 4 h to achieve the Ceo.zZra2O+rlysts were switched to heat in a flow of 20 m/min N2 atLa2O3 powder.200 °C and were iteratively pulsed at a desired temperatureThe prepared CeogZro2Or-La2O3 powders were impreg-until no more loss of O2 injected was detected.nated with the solution of Pd(NO3)2. Afterwards the materi-als were dried at 105 °C overmight and calcined at 500 °C for2 Results and discussion3 h in air, mixed with some water, ground and finally formedshurry. The resulting slurry was coated on a honeycomb cor-dierite (1.5 cm, Coming, America) and the excessive slurry2.1 Characterization of catalystswas blown away with compressed air, then dried and cal-X-ray difaction patterns of the samples are shown in Fig. 1.cined at 500 °C for 3 h in air. Finally, a monolithic catalystAl1 samples were calcined at 600 °C. All the diffactionwas obtained.peaks of catalysts are broad and dispersive. The charateris-tic diffraction peaks of all samples are basically in the same1.2 Determination of methanol decomposition activityposition as those of Ceo xZro2O2 cubic type rysallite, andThe reaction of gas phase methanol decomposition wasthe diffraction peaks of La2O3 do not appear, indicating thatperformed in a fixed bed continuous flow reactor operatingLa+ ions are completely dissolved into the CeO2-ZrO2 lat-under atmospheric pressure. The catalysts were placed in atices and form a steady CeO2-ZrO2-La2O3 solid solution orconventional tubular quartz reactor. Reduction of the cata-well disperse on the surface of supprtsl4. After introducinglysts was performned in a flow of 1.8 dm/h 5% H2 in N2 at5 wt.%La2O3, the four characteritic diffraction peaks shift to400 °C for 1 h before catalytic test. Then methanol dilutedlowera中国煤化工0.106 omn)is argrwith argon (MeOH, 15%; GHSV, 3400 h) was fed atthan thaomn (0.084 nm), La2+160- 300 °C. The outlet reaction gas was analyzed with anions aYHCNMHGesandresultedinon-lie gas chromatograph, equipped with a TDX-1 columnlttice expansion, interplanar distance increased and the dif-(2 m) and Porapak-Q column (2 m). Column switching wasfraction angles loweredl5si8. Futher increasing the La2O3JOURNAL OF RARE EARTHS, Vol 29, Na.6, Jun. 201146thanum oxide coverage of the surface of CoOrZrO2 solid11golution, PCexszZra2O-5 wt.%L&2O, psssed the highestspecifc surface area of 148.4 m/g and the largest pore vol-ume of0.25 cm/g, which are favorable to the disribution of220active components. The textural proetics of PdU20031Cen,xZra2Or-5 wt%La2Oz do grcat contribution to tho cn.hancement of catalytic activity.(3)。Fig. 2 shows the diferent pore size distributions of cata-(2)lysts. The pore size distributions of all catalysts are within0 30 nm. All catalysts show a bimodal pore size dsribution.The most probable pore sie of PdCo.sZrq2Ozis 4 nm,2030405067030whereas it is 10 nm about Pd/Cco.zZToxO2r5 w.%La2O; and201()PdCexzZro2O-10 wt.%La2O3 According to the references,Fig. I XRD ptterns of PCeo,xZro2O>-La2O0 catalystsmesoporous CeO2 and ZrO2 not only made active compo-(1) PdCogZqa2O2; (2) PdCegsZrazOrs wt%La2Oj;nents well disperse, but also promoted the mass transfer of(3) PdCeo Zro2O-10 w%La2O3catalysts6l. Therefore pore size distributio of PdCeo. gZro2Ox-5 wt.%La2O, is more benefial to mass transfercontent to 10 wt.%, position of diffractionlines do not than other two catalysts in methanol decompoition andchange either, implying that a part of La cations are incor-thereof improved reaction activity greatly.porated into the CeO-ZrO2 latie to form solid solution andTable 2 shows the OSC of Pd/CcgsZra;O-LaxO, catalyst8.the remaining La with the form of La2O3 are finely dispersedIt was observed that the addition ofLa increased the OSCofon the surface of the solid solution. This conclusion iscatalysts due to the formation of increased structure defectsconfirmed by the fact that no other dfraction peaks ofLa2O3 by the addition of La to CeOr ZrOz, which increased tho nbesides Cc0O2-ZrO2 solid solution was detected by XRDion-vacancy and promoted the migration ability of oxygenalyisl1920. Besides, no difraction peaks corresponding toions", When the content of La2O3 is 5 Wt.%, the OSCplladium (20= 40.0) and PdO (20 34.0)or PdO2(20- 54.60) reaches the maximum (357.1 umolg). With the increase ofare observed in the XRD pttens for all samples, sugsting La2O, content to 10 wt.%, the OSC dereascs (326.5 umolg),that plladiuam particles are wide dispersedon spprts surace. but are sil markedly higher than catalysts without doping ofThe contents and the ratios of metals in catalysts by ICPLa. It is well known that the higher OSC is, the strongertechnique are shown in Table 1. The theoretical calculating ability of releasing oxygen is, and then the reaction ofvalue was in accordance with experimental value basically.Ce*+→Ce'+ is easy to occur. The releasing of atomic oxygenN2 adsorption-desorpion (BET) measurement results areparially caused zero valent Pd to be oxidized into PdO,summarized in Table 2. All catalysts showed high specificwhich kept palladium in a state of highlyly active Pd'*t (22surface areas and large pore volumes after being calcined at Here, in the process of methanol decomposition, electrons600 C. The specific surface area of PdCevzZrczO2 is 114.6would shift from methoxy group to ectotodficicnt Pd* .m/g and the surface areas of the catalysts doped by lantha-Thus the C H bond in methoxy group was weakened, whichnum oxide increased significantly, indicating that La2O3 en-enhanced reaction rates of methanol decomposition,hanced the textural properties of CeOr-ZrO2 in agreementTPR profiles of the diferent catalysts are shown inFig.3.with resuts reported in lteretures2". But when La contentAs can be seen from the figure, all of the PdCosZra2Orexceeds to 5 wt%, the surface area and pore volumeLa2O, catalysts exhibit two reductin peaks. The sharp rdropped about 15%. This may be due to the excessive lan-duction peak below 100 °C may belong to the consump-Table 1 Contents and the ratios of metals in catalysts by ICPtechnique_CatalystsCe7(Atomie ntio w(Lx01%曾25只入2)PdCeazZro2O24.58:1 (4:1)0(0)"6.03(5YPCovZn:O-r10wt96LaO)3.93:1 (4:I户9.37(10*15ta The theorctical calculating value of metalsg 10Table 2 Textural properties ofPd/ CesZrazOrLa2OceatalystsSuwe/RwwOSC/Catalyts中国煤化工40 50(m'/g) (mlg) mm___ (umolg)_PdCe.sZra:O2114.60.223.684 298.9.YHC N M H Gor-aOcatalysPCenyZyO-s 毗9%[LaO,148.40.252992 357.1(1)PdCeo .ZTo 20;(2) PCogZoa2Or5 w%LaxO;_PdCe.,Z0:0-10 w%LaO131.1 0.203.245 326.5(3) PCgjZa2O2-10 wt%La2OsLI Xue et al, Effects ofLazOscontents on the PdVCeasZrazOrLazO3 catalysts for methanol decomposition547The spectra ofPd 3d lines for all samples are shown in Fig. 4.The binding energies of all catalysts are basically similarabout 336.0 eV and shown in Table 3. Recent XPS studiesl201of PdO and maeallic Pd showed that the binding energies ofPd 3dsn were respectively 336.8 and 335.2 eV. In this study,the binding energies of Pd 3dsz of all catalysts are signifi-cantly higher than that of Pd, but lower than that of PdO. It(3indicates that Pd exists in a partly oxidized state, which ismore active than zero-valent Pd. Research!I shows that the100 200 300 400 500 600 700 80breaking of C H bond absorbed in methoxy group is con-Temperature1 Csidered to be the rate-determining step (CHzO(a)+H(a)=Fig. 3 H2-TPR profile of all catalystsCH2O(a)+H()). When Pd exists in a partly oxidized state in(1) Pd/Ceo.zZro2O2; (2) PdCegZrx2O2-5 w.%La2O;catalysts, an electron will transfer from themethoxy group toPd, which weakens the C -H bond of the methoxy group, re-(3) Pd/ CesZTo2O2-10 wt.%La2O3sulting in the acceleration of the breaking of the C -H bond.tion of hydrogen for the reduction of PdO. The results areConsequently, it also contributes indirectly to a series of Pd/higher than references23.21. The insertion of Lat and Zr*CeoeZro2Oz-La2O3 catalysts in a state of high activity.into the CeO2 lttice promoted active ability of the ltticeThe OIs spectra for samples are presented in Fig. 5, andoxygen and accelerated the diffusion of oxygen ions in solidthe binding energy of O1s is listed in Table 3. There are threesolution from the bulk to the support surface and from thedifferent oxygen species in Pd/Ceo,zZro2O2-La2O3 catalystssupport to Pd particles. Furthermore, the increase of mobileaccording the results of the OIs in Table 3. The peaks locatedoxygen ions can contribute to maintain the PdO in a moreat 529.5- 529.8 eV and 531.1- -531.4 eV can be assigned tocationic state, and thus hindered the reduction of Pdol7.lattice o'^ and the pealks located at 532.4 532.7 eV are dueWith the addition of La, the reduction temperature of PdOto the presence of lttice defect oxygen or mobile oxygen'271shifs to high temperature, especially the reduction tempera-The active oxygen species are one of species in methanolture of PdO in PdCeo.gZto.2O2-5 wt.%I a2O3 is the highest,decomposition. In this situation even if the cationic palla-which indicates that there are strong interaction between Pddium is reduced to matallic Pd', the active oxygen willand Ceo.gZro2O2-5 wt.%La2O3 support29. The introductionre- oxidize zerovalent Pd' to a partly oxidized Pd"t, accordingof lanthanum oxide into Ceo.gZro2O2 lttices promoted theto the equation: Pd*+O- →Pd*. Pd*+ state is favorable tooxygen transfer from the bulk to the support surface andmethanol decomposition.from the support to the Pd particles. The increase of oxygen2.2 Catalytic activity for methanol decompositionmobility can facilitate the reduction of the CeO2 and main-tain the Pd in a more cationic Pd+ statel4. Moreover, theBy- products such as CH4, CH2OCHs and HCOOCH3 werereduction peak in 500600 °C is atributed to the reduction ofnot detected under reaction conditions. But a small amountsurface oxygen of CeO2. In the case of La modified catalysts,Table 3 Data of O1s and Pd 3dsn from XPS analysis of reducedthe peak shifted to lower temperature with the increase ofLacatalystsloading; the peak obtained on Pd/CexgZTo2O2-10 wt%La2O3OyveVPd 3ds/catalyst occurred lower than that of the un-promoted catalyst. Catalyts03sThis suggests that the addition of lanthanum to Pd/Ceo.gZr.2O2 increases the reducibility of Co,gZr02O2. As thePdCecxZrazO2529.8 531.4 532.7 336.0reduction of bulk Cett is more difcult,t the reduction tem-PdCeasZrgO-5 W.%La2Oy29.7 531.3 532.5 336.1perature rises generally above 800 °C, and the reduction peakPd/Ce.jZn2O-10 w.%La2O3529.5 531.1 532.4 35.8does not appear.回) Pd3dpb) Pd3d,(6) Pd3d,，Pd3d,.|客Pd3dePd 3d.s-y|3303353403433中国煤化工340345Binding energy 1 eVBinding cnergy/C N M H Gnergy/eVFig. 4 XPS of Pd 3d region for reduced Catalysts(间) PCesZrzO2; (b) PdICexgzZra2O2-5 wt%La2Os; (C) Pd/Cea gZrozO-10wt%La2O3i48JOURNAL OF RARE EARTHS, Vol 29, Na, 6, Jun. 2011国)Oi'-6↑4中O535525s35Binding energy/eVBinding energy 1 cVBinding energy1oVFig. 5 XPS ofOls region for reduced catalys(间) PCe,g2Zra2O2; (b) PdCeasZrx2O2-5 wt%La2O3; () PCexgZa2O-10 wt%La2O3of CO2 was detected at high reaction temperatures. It sug-the highest catalytic activity. The addition of lanthanum togests that methanol is decomposed into carbon monoxidePd/Ceo,gZro2O2 catalysts significantly improved the catalyticand hydrogen with high selectivity. Fig. 6 shows a plot ofactivity for methanol decomposition compared with Pd/methanol conversion versus reaction temperature of Pd/Ceo.gZTo2O2 catalysts. Also the addition of lathanum intoCen,gZro.2O-La2O3 catalysts. The methanol conversion of allCeO2-ZrO2 materials formed CeOz-ZrO2-La2O3 solid solutionsamples notably increased with the increase of reaction tem-with a steady cubic type cstallite, and improved texturalperatures. The activity of Pd/Ceo.zZto2Or5 wt%LazO3 andproperties of CeOr-ZrO2 oxygen storagc materials, The BETPd/Ceo,sZr.2O2-10 wt.%La2O3 which were all added with Lasuface area of the catalysts increased after introducingis obviously superior to that of Pd/ CensZra2O2. Pd5 wt.%LazO3, but declined afer introducing 10 wt.%La2O3,Ceo,gZro2O2-5 wt.%LazO3 catalyst shows enbanced activityFurthermore, with the addition of La, the reduction termpera-both at low temperature and high temperature as well. Theture of PdO increased, especially the reduction temperatureresult suggests that the addition of La to PdCeo.xZro2O2of PdO in Pd/CeogZro2O2-5 wt.%La2O3 achieved the highest,strongly affected the methanol decomposition activity ofindicating that there are strong interaction between Pd andcatalysts. The insertion of La+ into the CeO--ZrO2 ltticeCeo.8Zro.2Or-5 wt.%La2O3 support,increased the OSC, promoted active ability of the ltticeoxygen and accelerated difusion of oxygen ions in the solidReferences:solution from the bulk to the support surface and from thesupport to Pd particles. The increasing of oxygen transfer[1] Cheng W H. Development of methanol decomposition cata-can help to maintain more Pd in cationic state, which is ad-lysts for production of H2 and Co. Acc. Chem. Res, 19,9 32:vantageous to activityl28l. Lifetime tests have demonstratedthat the conversion of methanol over all Pd/Ceo.sZro2Or-[2] Matsumura Y, Shen W G Methanol decomposition and synthe-La2O3 catalysts maintains above 95% after continuous worksis over plladiuom catalysis. Top, Catal, 2003, 22(3-4): 271.[3] Motoi s, Hideaki H, Takehiko 1. Mecthanol decomposition overfor 72 h.Pd simultaneously deposited with supprt oxide onto quartzplates. Appl. Catal, 2001, 207: 191.100. Ppd/CeZ02O2[4] Shen W J, Matsumura Y. Interaction between plladium and◆Pd/Ce% Zx202-5毗% La2O,the support in Pd/CcO2 prepared by depsitin-precipiation- Pd/CoZT2O2-10 wt% LaO,method and the catalytic activity for methanol decomposition.J. Mol Catal. A: Chem, 200,0 153: 165.o[5] Liu Y Y, Hayakawa T, Ishii T, Kumagai M, Yasuda H, SuzukiK, Hamakawa s, Murata K. Methanol decompoition to syn-宫40thesis gas at low temperature over palladium supporteod onceria-zirconia solid solutions. Appl. Catal, A, 2001, 210: 301.[6] Kapoor M P, Anuj R Yasuyuki M. Methanol decompositionover palladium supported mesoporous CeO2-ZrO2 mixed 0x-ides. Micro. Meso. Mater, 2001, 4445: 565.180 200 220 240 260 280 300 320 340[7] Sun K P, Lu W W, Wang M, Xu X L. Characterization andTemperature/ ccatalytic performances of La doped Pd/CcO2 catalysts forFig. 6 Convesion of methanol decomposition at dfferent tempera-methanol decomposition. Appl. Calal, A, 2004, 268: 107.tures over Pd/Ceo.gZr2O2-La2O3 catalysts[8] Yan中国煤化mnd La2O-modified)sition at low Tem-3 ConclusionsperaYHC N M H GoOr-modifed Pd/rAl2O3 catalyst. Chin. J. Catal, 2001, 22(3): 283.In short, PdCeosgZto2O2-5 wt.%La2O3 catalyst exhibited[9]LiYL,ZhangXY,LongEY,LiHM,WuDD,CaiL,GongLIXue et al, Effects ofLazO; contents on the PdVCea sZrszOr-La;Oz catalysts for methanol decomposition549M C, Chen Y Q. Infucnce ofCcO2 and La2O, on propertics of38.palladium catalysts used for emission control of natural gas[19] Weng X L, Perston B, Wang X z, Abrahams I, LinT, Yang SEvehicles. J. Nat. Gas, Chem, 2009, 18: 415.Synthesis and characterization of doped nano- sized ceria-zir-[10] HongJ s, Kim S J, Han W K, Kang s Q Thermal properies ofconia solid soutions. Appl. Catal, B, 2009, 90: 405.La2Oz-YSZ powder fabricated by bheterogencous precipitation.[20] Papavasilioua A, Tsetsckoua A, Matsoukab V, Konsolakisb M,J. Alys Compd, 2009, 486: 543.Yentekakisb I V. An investigation of the role of Zr and La[1] Liu R H, Zhang C M, Ma J X. High thermal stable gold cata-dopants into Cent ,Zr,La,O enriched r-Al2O3 TWC wash-lyst supported on La2O2 doped Fe2O3 for low-temperature COcoats. Appl. Catal, A, 2010, 382: 73.oxidation. J. Rare Earths, 2010, 28(3): 376.[21]LiM,LiuZGHuYH,WangMT,LiHQ.Efeetofdoping[12] Zhang X Y, Long E Y,LiYL, GuoJ X, Zhang LI, Cong MC,elements on catalytic performance of CeO2 ZrO2 solid solu-Wang M H, Chen Y Q. CeO-Zr0-La2O)-Al2O3 compositetions. J. Rare Earths, 2008, 26(3): 357.oxide and its supported palladium catalyst for the treatment of[22]WangXH,LuGz,GuoY,QiaoDs,ZhangZGGuoYL,Liexhaust of natural gas engined vehicles. J. Nat. Gas. Chem,C Z. Propeties of CeO-ZrO2 solid solution supprted on2009, 18: 139.Si-modified alumina and its aplication in Pd catalyst for[13] Yue L, ZhaoL H, Zhang Q B, Zhang T, Luo M F Catalyticmethane combustin. Chin. J. Catal, 2008, 29(10); 1043.combustion of toluene over Pd-based monolithic catalysts with[23] Barera A, Viniegra M, Fuentes s, Diaz G The role of lanthanaa novel washcoat Ce.gZo.sLaasOg J. Rare Earhs, 2009,loading on the catalytic properties of Pd/Al2O-La2O3 in the27(5): 733.NO reduction wih H ApplL. Catal, B. 2005, 564); 279.[14]GuoJX,YuansH,GongMC,ZhangL,WuDD,ZhaoM,[24] Luo M F, Zheng X M. Redox behaviour and catalytic proper-Chen Y Q. Influence of Cen.gZr, s 101.95 solid solution onties of Ceo gZrp ;Or-supported plladium catalysts. Appl. Catal,the performance of P-Rh three-way catalysts. Acta Phys-A, 199, 189(1): 15.Chim. Sin, 2007, 23(1): 73.[25] FanJ, Wu X D, Yang L, Weng D. The SMSI between sup-[15] Wang Q Y,LiG F, Zhao B, Shen MQ, Zhou R X. The eftet ofported platinum and CeO>-ZrO>2-La2O3 mixed oxides in oxida-La doping on the structure ofCezZqagO2 and the catalytic per-tive atmosphere. Catal Today, 2007, 126: 303.formance of its supported Pd-only thee-way catalyst. Appl.[26] Xiao L H, Sun K P, Xu X L, Li X N. Low-temperature cata-Catal, B, 2010, 101: 150.lytic combustion of methane over Pd/CeO2 prepared by depo-[16] Wang Q Y, Li G F, Zhao B, Zhou R X. Synthesis of Lasition-precipitation method. Catal. Commun, 2005, 6(12):modified ceria zirconia solid solution by advanced supercriti-79cal ethanol drying technology and its application in Pd-only[27] WuGs, Wang LC, Liu YM, Cao y, Dai W L, He H y, FanKthree-way catalyst. Appl. Catal, B, 2010, 10: 516.N. Implication of the role of oxygen anions and oxygen vacan-[17]WangHR,ChenYQ,ZhangQL,ZhuQC,GongMC,Zhaocies for methanol decomposition over zirconia supported cop-M. Catalytic methanol decomposition to carbon monoxide andper calyts. Appl. Sur Sci, 2006, 253: 974.hydrogen over Pd/CeO2-ZrO2-La2O3 with dfrent Ce/Zr mo-[28] Borasio M, Rodnguez 0, Fuente D, Ruprechter G Freund H.lar ratios. J. Nat. Gas. Chem, 2009, 18: 211.In situ studies of methanol decomposition: and oxidation on[18]FanJ, WuX D, Wu X D, Liang Q, Ran R, Weng D. ThermalPl(111) by PM-IRAS and XPS spectroscopy. J. Phy. Chem. B:ageing of Pl on lowsufac-arca CeOQ-ZrO-La2O3 mixed ox-Lett, 2005, 109: 17791.ides: Effet on the OSC performance. Appl. Catal, B, 2008, 81:中国煤化工MYHCNMHG