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Composite supports Zr0.5Al0.5O1.75 modified by metal oxides,such as La2O3,ZnO,Y2O3 or BaO,were prepared by co-precipitation method,and palladium catalysts supported on the modified composite supports were prepared by impregnation method.Their properties were characterized by X-ray diffraction (XRD),NH3 temperature-programmed desorption (NH3-TPD),H2 temperature-programmed reduction (H2-TPR),N2 adsorption/desorption,and CO-chemisorption.The catalytic activity and the resistance to water poisoning of the prepared Pd catalysts were tested in a simulated exhaust gas from lean-b natural gas vehicles with and without water vapor.The results demonstrated that the modified supports had an apparent effect on the performance of Pd catalysts,compared with the Pd catalyst supported on the unmodified ZrAl.The addition of ZnO or Y2O3 promoted the conversion of CH4.In the absence of water vapor,Pd/ZnZrAl exhibited the best activity for CH4 conversion with the light-off temperature (T50) of 275 ℃ and the complete conversion temperature (T90) of 314 ℃,respectively.However,in the presence of water vapor,Pd/YZrAl was the best one over which the light-off temperature (T50) of methane was 339 ℃ and the complete conversion temperature (T90) was 371 ℃.These results indicated that Pd catalyst supported on the modified composite ZrAl support showed excellent catalytic activity at low temperature and high resistance to H2O poisoning for the exhaust purification of lean-b natural gas vehicles.