Catalytic methanol decomposition to carbon monoxide and hydrogen over Pd/CeO2-ZrO2-La2O3 with differ

Available online at www.sciencedirect.comJIUPIUL.FScienceDirectSNGCFNATURALGASCHEMISTRYEL SEVIERJoumnal of Natural Gas Chemistry 18(2009)211-216www. elsevier.com/locate/jngcCatalytic methanol decomposition to carbon monoxide and hydrogenover Pd/CeO2-ZrO2-La2O3 with different Ce/Zr molar ratiosHairong Wang，Yaoqiang Chen, Qiulin Zhang，Qingchao Zhu，Maochu Gong，Ming Zhao*Kay Laboratory of Green Chemistry & Technology of Ministry Education, College of Chemistry, Sichuan University, Chengdu 610064, Sichuan, China[ Received February 5, 2009; Revised March 27, 2009; Available online June 24, 2009]AbstractThe catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO2-ZrO2-La2O3 mixed oxides with different Ce/Zr molar ratios wereinvestigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photocletron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), X-ray dffractiono (XRD) and Pd dispersion analysis were used for their characterization. PdCeo.76Z0.18La0.06O1 97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPSshowed that there was lttice defect oxygen or mobile oxygen. According to the result of 0 Is measurements the lttice defect oxygen or mobileoxygen helped to maintin Pd in a partly oxidized state and increased the activity for methanol decompositin. The PCo.7670.18L30.06O1.97catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260 °C, which was about 20- -40 °C lower thanother catalystsKey wordsmethanol decomposition; plladium; CeO2-ZrO2-La2O3; XPS; hydrogen; carbon monoxide1. Introductionited space in the engine fuel compartment and limited temper-ature of the exhaust heat, especially at cold start, the methanolRecently the decomposition of methanol to H2 and COdecomposition catalysts are required to be active at low tem-has drawn growing attention. The decomposition product isperature [5]. For base metal catalysts, its low temperature ac-a cleaner and more efficient fuel than gasoline and undecom-tivity and selectivity to CO and H2 are poor. The Pd-based cat-posed methanol for internal combustion engines of automo-alysts seem to be preferred and their activity is largely affectedbiles. The decomposition may be brought about by makingby the supports. Kapoor [6] and Liu [7] et al. prepareduse of engine exhaust heat, and this would increase the heatingPd/CeO2-ZrO2 catalysts. A more active Pds+(0< 8 <2) statevalue of the fuel. The methanol decomposition is also attrac-could be maintained. Moreover, palladium particles with bet-tive as a source of hydrogen and/or synthesis gas for chemicalter distribution and stability were on the surface of CeO2-ZrO2processes or as an ecological fuel for gas turbines and fueloxides supports. Sun [8] and Yang [9] et al. reported thatcells. Moreover, it is an endothermic reaction as well as re-the addition of lanthana significantly improved the activity ofversible reaction, which can operate in a suitable temperaturePd supported catalysts. Besides, lanthana could enhance therange. The equilibrium conversion of methanol decomposi-dispersion of active component and increase the mumber oftion reaches around 100% at 473 K at atmospheric pressure.active sites. Guo et al. [10] prepared Ceo.3sZro.ssLao. 1oO1.95solid solution, which improved thermal resistance and showedCH;OH→CO+ 2H2△H = 90.7kJ/molgood redox property. However, up to now, there are few re-Various metals like nickel, copper, iron, platinum and pal-ports on the catalytic behavior of methanol decompositionladium supported on Al2O3, SiO2, TiO2, ZrO2, CeO2, activedover Pd/CeO2-ZrO2-La2O3. The goal of this paper is to inves-carbon and synthetic clays were reported to be effective fortigate the surface properties and catalytic performances overmethanol decomposition [1-4]. However, because of the lim-Pd/CeO--7x0--1 g0z for methanol decomposition.中国煤化工●Crresponding author. Tel: +86-28-85418451; Fax: +86-28-85418451; E-mail: micFoundation item: the National Natural Science Foundation of China (20773090)TYHC N M H Ge Docon Pogam ofHigterEducation of China (20070610026, 2010000)Copright@2009, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. All rights reserved.doi:10.1016/S1003-9953(08)60109-7212Hairong Wang et al/ Journal of Natural Gas Chemisty Vol. 18 No.220092. Experimentalments were carried out in a conventional system equippedwith a thermal conductivity detector. All samples (100 mg)2.1. Catalyst preparationwere pretreated in a quartz U-tube in a flow of pure N2 at400°C for 45 min, and then cooled. The reduction was car-The CeO2-ZrO2-La2O3 samples with different CelZr mo~ried out in a flow of H2 (5%, diluted with N2) from 50°C tolar ratios were prepared by co-precipitation method from900 °。C with a linear heating rate of 8 °C/minthe corresponding chemicals: Ce(NO3)3-6H2O, Zr0CO3Pd dispersion was measured after reducing the sam-and La(NO3)3-6H2O at a nominal composition. The pre-ple (200 mg) at the appropriate temperature (400。C) undercursors were mixed in an aqueous solution, respectively,5%H2-95%N2 flow for 1 h. The remmant H2 was driven offand an appropriate amount of fresh H2O2 was added towith argon at 420 °C for 30 min, then the sample was cooledthis mixed salt solution. Then the mixed salt solutiondown to room temperature under argon flow. Finally, pulse ofwas added dropwise to a new container with a mixedCO was injected up to the breakthrough point. Pd dispersionsolution of ammonia and ammonia- carbonate aqueous so-was evaluated from CO consumption.lution, to reach a pH value of 9.0. The precipitatesThe X-ray photoelectron spectroscopy (XPS) experi-were filtered, washed, dried, and calcined at 600°C forments were carried out on a spectrometer (XSAM-800,4h. Finally, Co.o0.4La0.oO1.97, Ce.64Zxo 3oL 80.0601.97,KRATOS Co) with Mg K。radiation under UHV. All samplesCeo.76Zro.18L80.0601.97 and Ceo,8sZr.o9La0.o6O1.97 powderswere pretreated in a flow of 5%H2-95%N2 at 400°C for 1 h,and cooled to room temperature. The binding energy was de-were obtained.The prepared CeO2-ZrO2-La2O3 powders were impreg-termined by reference to the C ls binding energy of 284.8 eV.nated with the aqueous solution of Pd(NO3)2. The materi-als were dried at 105 。C overnight and calcined at 500 °C3. Results and discussionfor 3h in air, then added some water, ground and finallyformed a slurry. The resulting slury was coated on a hon-3.1. Characterization of catalystseycomb cordierite (1.5 cm', Comning, America) and the ex-cessive slurry was blown away with compressed air, dried,Figure 1 shows representative XRD pattermns for the sam-calcined at 500°C for 3h in air. A monolithic catalyst wasples. Four characteristic diffraction peaks are observed and in-thus obtained (catalyst amount 0.2 g, Pd loading 1.4 wt%).dexed as CeO2-ZrO2 cubic type crytallite. All the diffractionpeaks for the product can be indexed to (111), (200), (220)2.2. Catalytic testsand (311) crystal faces, corresponding to a face centered cu-bic (fcc) fluorite structure ofCeO2-ZrO2. No separated La2O3Gas phase methanol decomposition was performed inare detected by XRD in the 20 region from 10 to 909, whicha fixed bed continuous flow reactor operating under atmo-indicates that La ions are doped into CeO2-ZrO2 frameworkspheric pressure. The monolithic catalysts were placed in aforming the CeO2-ZrO2-La2O3 solid solution. Besides, notubular quartz reactor. The samples were reduced in a streampeak of Pd is found in the XRD patterns for all of the sam-of 5% hydrogen (diluted with nitrogen) at 400 °C for 1 h (flowples, suggesting palladium particles are well dispered on therate 1.8 dm3/h). Then methanol diluted with argon (MeOH,supports.15%; GHSV, 3400 h-) was fed at 160- -300°C.The outlet reaction gas was analyzed with an on linegas chromatograph (GC2000I1 with TCD). A TDX-1 column(2 m) was used for the analysis of H2. CO, CH4 and CO2, andPorapak-Q column (2 m) was used for CH3OH, CH3OCH3(4)and HCOOCH3.M..2.3. CharacterizationX-ray diffraction (XRD) patterns were obtained on aD/MAX-Ra rotarory diffractometer, using Cu K。radiation(入=0.15406), 50kV and 180 mA; samples were scanned(:from 20 equal to 20° up to 90.A人The BET surface area and pore size distribution were中国煤化工业measured by nitrogen adsorpotion -desorpotion at 77 K usinga ZXF-6 instrument (Xibei chemical institute, China). To des-MYHCNMHG780orb surface impurities, the samples were degassed for 1h atFlgure 1. XRD patterns of_ Pd/CcO2-ZO2-La2O3 catalysts. (350 °C in vacuum before measurement.Temperature-programmed reduction (H2-TPR) experi-PdCo.oZ0.44L4.09.97，(2) Pd/Ceo.6zZo.3oLao.0oO1.97. (3PCO.6Zo.18EL30. 0601.97. (4) PCcC.9.sg5o.0.0.01.9Joumal of Nanunal Gas Chemisty Vol. 18No.2 2009213N2 adsorption-desorption (BET) measurement results arehas stronger metal-support interaction.summarized in Table 1. From Table 1 we can see that allFigure 2 it can be seen that larger H2 consumption ofcatalysts show high specific surface areas and large pore vol-Pd/Ceo. 767Zro.1gL80.06O1.97 than those of other samples im-umes. Pd/Ceo. 76Zro 18Lao. o6O1.97 has the highest specific sur-plies that PdO is well dispersed on the Ceo.76Zro. 18L80.06O1.97face area and largest pore volume, namely 149.5 m2/g specific support. It is in agreement with the data on Pd dispersion.surface area and 0.25 m/g pore volume. The textural proper-The reduction peaks at 350- 550°C are attributed to the re-ties such as specific surface area, pore volume, play an impor-duction of surface oxygen species adsorbed on CeO>2-ZrO2-tant role in the performance of catalytic activity. The resultsLa2O3. With the increase of Ce content, the surface oxy-indicate that Pd/Ce.76Zro.18L 80.06O1.97 has excellent texturalgen reduction peaks first shift to lower temperature and thenproperties, which are consistent with the catalytic activity.move to higher temperature. The reduction temperature fallsto the lowest value with 0.76 Ce content (molar fraction).Table 1. Textural properties of Pd/CeO2-ZrO2-La2O3 catalystsIt may be due to the increased oxygen transfer, which pro-Rnemmotes the reduction of Ce4+. Moreover, it is generally ac-Catalyst?/g)(cm/g)cepted that the oxygen reduction easily takes place at the in-0.233.264terface between the metal and the support, when the strongPd/Ceo. 6470.0La0.o01.97122.40.213.049PCo.767Z.18L0.0601.97149.50.252.892metal-support interaction exist in the catalysts. The peaks atPdUCco. 8sZro 0L06O1.909.124.20.182.837650-850 °C are attributed to the reduction of the lttice oxy-gen. Pd/Ceo 8sZo.c9Lao.o01.97 catalyst shows a broader hy-drogen consumption peak in higher temperature, it may be dueThe TPR profiles of all catalysts are shown in Figure 2.to the high CeO2 content.The TPR profiles of all catalysts with different Ce/Zr ratiosThe Pd dispersion was tested at room temperature byexhibit similar spectra. There are three reduction peaks pre-CO chemisorption on reduced samples. The surface area ofsented. The reduction peak at 100- 150°C may belong toPd was calculated from the amount of CO ireversibly ad-the consumption of hydrogen on the reduction of PdO, whichsorbed, assuming the site density of Pd as 0.060 nm2/atomindicates variation in the distribution of PdO with supportand the stoichiometry of one CO molecule per Pd atom ex-composition. According to the published reports ([11-13],posed on the surface [14,15]. The mean particle size of palla-the TPR profiles of Pd supported catalysts showed that PdOdium was tentatively calculated from Co adsorption, assum-was reduced at 60- 90°C. The reduction temperatures foring that all the palladium particles are spherical and dispersedPdO in our catalytic system are higher than those in the lit-n the surface [6]. All catalysts show high Pd dispersioneratures especially for Pd/Ceo.76Zro.1gLa0.06O1.97. It may beand the percentage of exposed Pd on CeO2-ZrO2r-La2O3 in-due to that La3+ and ZA4+ dissolved into the CeO2 ltiecreased with increasing content of Ce, while the content ofwhich produce an accelerated diffusion of oxygen ions fromCe is up to 0.85 (Pd/Ceo.8sZro.oL 20.0601.97), and the Pd dis-the bulk to the supports surface and from the support to Pdpersion drops to 38.1 1%. Pd/Ceo 76Zro 18La0.o6O1.97 exhibitsparticles [8]. Furthermore, the promoting of oxygen transferthe highest Pd dispersion (49.22%) and smallest Pd particlecan help to maintain PdO in a more cationic state, and thussize (2.81 nm). With the same loading of Pd, large areas ofhinder the reduction of PdO. The PdO reduction temperaturesupport and small diameter of Pd are crucial to the Pd dis-of Pd/Ceo.76Zro.18La0.06O1.97 is higher than those of the oth-ers, which indicates that Pd and Ceo.76Zro.18La.0oO1.97 oxidepersion. It was reported that smaller Pd particles interactedstrongly with the support [16]. The percentage exposed of Pdon Ceo.76Zro.18La0.o601.97 is higher than those on others be-cause of the different interaction between the metal ions andthe supports [17], and Pd/Ce.76Zro.18L80.06O1.97 exhibits thestrongest interaction between the metal ions and the supports.It was reported that higher dispersion caused the higher ac-tivity for methanol decomposition [18]. The more palladium(4)exposed on the surface; the more active sites were obtained.The results in are in accordance with our activity test order._3Table 2. Pd dispersion of Pd/CeOx-ZrOx-La2Os catalystsDesigned Pd Pd dispersion Pd particleloading (wt%)(%)size (nm)Pd/Ceo.snZro. 4La.oO.1.42.393.26PdICeo中国煤化工4.413.08PUICco9.222.81)0 500 600 700 800 900Pd/CeoYHCN MH G_ 38.113.63Temperature(C)Figure 2. H2-TPR profles of all catalysis. (1) Pd/Ceo soZro. 4La0.0O1.9nIn order to understand the chemical states of Pd on(2)_ Pd/Ce0.64Zro. 3oL0.06001.71,(3) PdCe.76Zo.18L0.06O1.97， (4)the catalysts, Pd/CeO2-ZrO2-La2O3 catalysts were stud-214Hairong Wang et al/ Journal of Natural Gas Chemistry VoL 18 No.22009ied by XPS after reduction. Figure 3 presents the XPSspectra of Pd 3d. The valence states of palladium areasymmetry on the peak shape, which suggested that the Pddifferent in the four samples. Pd/Ceo soZr.44La.0.0.90 (3)3ds/2 peaks might consist of more than one species and itand Pd/Ce0.64Zro.3oLa0.o6O1.97 (b) catalysts show only oneis deconvoluted into two peaks (Pd 3ds/2(1); Pd 3ds/2(2)).Pd 3ds/2 peak, however PdCeo.76Zro.18L80.06O1.97 (c) andThe BE values of Pd 3ds/2 and Ce 3ds/2 peaks are tabulatedPdCe.s75.09Laco.ocOn.9n (d) catalysts show large value ofin Table 3.Zr 3pnaZr 3pn(aZzr3pn ()Pd 3dsnPd 3dnPd3c330332334 336 338 340 342 344 346 348 350330332334336338340342344346348350Binding energsy (eV)Binding energy (eV)Zz3PmnZr 3pvn”(c乙3px:Zzt3pvn (d)Pd 3ds(1)Pd 3dx(1)|Pd 3dsx(2)Pd 3dxnPd 3d3nPd3dn I 1Pd 3dsa|330 332 334 336 338 340 342 344 346 348 350330 332334 336 338 340 342 344 346 348 350Figure 3. XPS of Pd 3d region for redued calys. (a) PdCeo soZo.4Lo. aoO.97. (0) PdCo.4Zro 3oa.o01.97. (c) Pdce.g6Z101.a.601.97. (d)PCo.8s2Z0.09La0.o6O1.97Table 3. Data from XPS analysis of reduced catalystsC-H bond of the methoxy group will be weakened, result-ing in the acceleration of the abstraction of the C-H bond [7].CatalystPd3ds/2 Pd3ds/2(2) Ce 3dy/2=The BE values for Pd 3ds/2(2) of PdCo.76Zro.18L 80.060O1.97335.51882.47(c) and Pd/Ceo.sZro.o9La0.06O1.7 (d) are higher than that ofPdCeo. 64Z0.30L80.06Oz336.00882.77PdO. This result implies that Pd2+ cations in the present cat-Pd/Ceo.76Zro. 18La0.6Oz335.40337.00882.83alyst system are much more cationic than PdO. Usually, thisPd/Ceo.8sZro.09L80.06Ox335.60883.08phenomenon can be understood as the strong metal-supportRecent XPS study reported that the binding energies ofinteraction effect. That is the Pd~O bonding does not be-PdO and metllic Pd0 are 336.8 eV and 335.2 eV, respectivelylong to Pd-0-Pd but to Pd-0-Ce in the Pd-CeO2-ZrO2-La2O3[19]. The binding energies of Pd 3ds/2(1) for all Pd/CeO2-[8]. The strong interaction between palladium and supportZrO2-La2O3 catalysts are 335.4- 336.0eV, higher than thatcan reduce the activation energy of the rate-determining stepof Pd0. It indicates that Pd takes a partly oxidized state. Thein the methanol decomposition [6]. Thus, the reducibility ofpartly oxidized state of Pd is more active than zero-valentpa中国煤化工-La2O3 catalysts are de-Pd for methanol decomposition. The abstraction of the C-H scengYHIn other words, palla-bond in the adsorbed methoxy group CH3O (CH3O (ad) +diunC N M H G06O1.97 is reduced most .H (ad)= CH2O (ad) + H2 (g)) is the rate determining step.difficultly which is in accord with H2-TPR.When Pd takes a partly oxidized state in the catalysts, anThe 0 1s spectra for the samples are presented in Figure4.electron is withdrawn from the methoxy group to Pd and theThree different oxygen species can be found which are locatedJoumal of Narural Gas Chemisty Vol. 18 No.22009215at 529.18- -529.71 eV, 530.56- -531.13eV, 531.68- -532.54eVgen for methanol decomposition. In this situation even if pal-respectively. The peaks located at 529.18- 529.71eV andladium oxide has been reduced to metallic Pd', the active oxy-530.56- 531.13eV can be assigned to lttice 02- and the lat-gen might have re-oxidized Pd0 to Pd oxide state according toter is due to the presence of lttice defect oxygen or mobilethe fllowing scheme [19]: Pd0 +0-→Pd6+; Pd'+ is in favoroxygen [20], which can be proposed as an active state of oxy-of methanol decomposition.529.18 '529.4a)\530.56 531.68(530.82/ 532.17WuMA4M524 526 528 530 532 534 536 538Binding energy (eV)29.45c)(d)529.7530.72t 532.5431.13)32.27yBinding encrgy (eV)Figure 4.0 1s spectra of reduced catalys. (间) Pd/Ceo. soZr.L4a.o01.7. (0) PdCo.6Zro. 3020.01.7.0 (2) PC.7Z1018.0.60.97. (d)PCe.sS7o.o9La0.06O1.9n3.2. Catalytic activity for methanol decomposition00 t(3)Methanol was selectively decomposed to carbon monox-ide and hydrogen over the series of Pd/CeO2-ZrO2-La2O380 fcatalysts. No by-products such as CH4, CH3OCH3, and4)HCOOCH3 were detected under the reaction conditions.But small amount of CO2 was detected at high reaction60temperatures./)Figure 5 shows a plot of methanol conversion versus re-action temperature. As expected, the catalytic activity of allsamples is found to increase with the rising of reaction temper-20ature. Also it can be seen that catalytic activity is enhanced atlow temperature with increasing Ce content ((1)-→+(2)- +(3).PdCe.76Zr0.18Lao.o6O1 .97(3) shows obviously advantageous中国煤化工1 260 280 300activity. A temperature as low as 260°C is needed for100% conversion over Pd/Ceo.76Zro.18L80.o6O1.97(3) cata-YHCNMH Glyst, while it is 300°C for Pd/Ceo. soZro 44L 20.06O.97(1) andFlgure 5. Methanol decomposition over PdCeO2-ZrO2-La2O3 cata-Pd/Ceo.64Zro. 30La0.0601.9(2). Further increasing Ce contentlysts with different CeZr molar ratios. (1) Pd/Ceo. soZ0.44L420.06O1.9r) Pd/Ceo.64Zr0.30L2o.06O1.97， (3) PdCo.7Zr.18L0.06O1.97. (4)lead to lower catalytic activity (3)- +(4) , the 100% conver- Pd/Ceo. 8sZzo 0a060.0216Hairong Wang e al/ Jounal of Natunl Gas Chemnisty VoL. 18 No.2 2009sion of PdCeo.sZro.osLa0.0601.97(4) is at 280°C. This factPd 3d for four catalysts suggested the presence of partly oxi-suggests that Pd/CeO2-ZrO2-La2O3 catalysts with differentdized palladium which favored the catalytic function. Besides,Ce/Zr molar ratios strongly affect methanol decompositionPd/Ceo.76Zro.18La0.06O1.97 catalyst showed stronger metal-activity. The methanol conversion showed a maximum valuesupport interaction than others. Co adsorption showed thatwhen the molar ratio of Ce4+ to Zr4+ was 0.76/0.18.Pd was well dispersed and distributed mainly on the surfaceThe methanol decomposition was considered to occur ac-of Pd/Ceo 76Zro.18La0.o6O1.97 catalyst. The more palladiumcording to the fllowing schemes [7]:exposed on the surface; the more active site was obtained. .CH3OH(g) = CH3O(ad) + H(ad) (1)CH3O (ad)+ H(ad) = CH2O(ad) + H2(g)ReferencesCH2O(ad) = CHO(ad) + H(ad)(3) .[1] Matsumura Y, Tode N, Yazawa T, Haruta M. J Mol Catal A,CHO (ad) = CO(ad) + H(ad)1995, 99: 183CO(ad) = CO(g)(52] Nanzoli M, Chiorino A, Boccuzzi F. Appl Catal B, 2004, 57:2H(ad) = H2(g)(6)01[3] Cao D, Lu G Q. Wieckowski A, Wasileski s A, Neurock M. JIn the elementary steps above, the Reaction (2), the abPlhys Chem B, 2005, 109: 11622straction of C- -H bond in methoxy group was considered to4] Borchert H, Jurgens B, Nowitzki T, Behrend P, Borchert Y,be the rate- determining step. A partly oxidized state of Pd isZielasek V, Giorgio S, Henry C R, Baumer M. J Catal, 2008,more active than zero-valent Pd for this step. When Pd takes256: 24a partly oxidized state in the catalysts, an electron is with-[5] Cheng W H. Acc Chem Res, 199, 32: 685drawn from the methoxy group to Pd and the C-H bond of the[6] Kapoor M P, Raij A, Materials Y. Micropor Mesopor Mater,methoxy group will be weakened, resulting in the acceleration2001, 44-45: 565of the abstraction of the C-H bond. As discussed above, the[7] Liu Y Y, Hayakawa T, Ishii T, Kumagai M, Yasuda H, Suzukiparly oxidized state of Pd was detectable from the XPS anal-K, Hamakawa s, Murata K Appl Caral A, 2001, 210: 301ysis. Besides, the BE values for Pd 3ds/2(2) of the catalysts[8]SunKP,LuWW,WangM,XuXL.ApplCatalA,2004,268:used are higher than those for PdO. Usually, this phenomenon07can be understood as the effect of strong metal- support inter-[9] Yang C, RenJ, Sun Y H. Catal Lett, 2002, 84: 123action, which would hinder the reduction of palladium. Com-[10]GuoJX,YuansH,GongMC,ZhangL,WuDD,ZhaoM,Chen Y Q. Acta Phys Chim Sin, 2007. 23(1): 73bining with H2-TPR and XRD, it is seen that La3+ dissolved[11] Yue B H, Zhou R X, Wang Y J, Zheng X M. Appl Sur Sci, 2006,into the CeO2-ZrO2 lttice and formed CeO2-Zr0O2-La2O3252: 5820solid solution, and this would produce an accelerated diffusion[12] Brrera A, Viniegra M, Fuentes s, Diaz G. Appl Caral B, 2005,of oxygen ions from the bulk to the support surface and the56: 279support to Pd pricls. Furthemore, the increasing of oxy- [131 LuoM F, Zheng xM. Appl CaalA, 199 189: 15gen transfer can help to maintain Pd in a more caionic state. [14] Sasaki M, Hamada H, Ito T. Appl Catal A. 2001, 207: 191On the other hand, the Pd/Ceo.76Zro lLa0.o6O1.97 catalyst has [15] Shishido T, Sameshima H Takehira K. Top Catal, 2003 22(3-a highest BET surface area and best Pd dispersion capability,4): 261which may be the reason why the Pd/Ceo.8sZro.ogLa0.06O1.97 [16] Usami Y, Kagawa K, Kawazoe M, Matsumura Y, Sakurai H,catalyst showed the highest actity.Haruta M. Appl Catal A, 1998, 171: 123[17] Lee C, Yoon H K, Moon S H, Yoon K J. Korean J Chem Eng,1998, 15(16): 5904. Conclusions[18] Yang C. Ren J, Sun Y H. Cuihua Xxuebao (Chin J Catal), 2001,22(3): 283In the catalysts studied herein, Pd/Ceo.76Zro.18La0.o601.97[19] XiaoL H, Sun K P, Xu X L, Li X N. Catal Commun, 2005, 6:catalyst produced the highest catalytic activity in the selec-796tive decomposition of methanol to co and H2. The 100% [20] Wang X H, Lu G z, Guo Y, Qiao D s, Zhang zG, Guo YL, Liconversion was reached at 260°C. The binding energies ofC z. Cuihua Xuebao (Chin J Catal), 2008, 29(10): 1043中国煤化工MYHCNMHG