Pd catalysts supported on modified Zr05Al05O1.75 used for lean-burn natural gas vehicles exhaust purification

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-burn 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 °C and the complete conversion temperature (T₉₀) of 314 °C, 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 °C and the complete conversion temperature (T₉₀) was 371 °C. 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-burn natural gas vehicles.