Effects of ZnO content on the performance of Pd/Zr0.5Al0.5O1.75 catalysts used in lean-burn natural gas vehicles

Abstract

Mixed oxides obtained by adding varying amounts of ZnO into Zr0.5Al0.5O1.75 were used as supports to prepare 1.5% Pd catalysts. The catalyst activity and H2O tolerances of the catalysts were evaluated in a gas mixture simulating the exhaust of lean-burn natural gas-fueled vehicles. The catalysts were further characterized by N2 adsorption-desorption, X-ray diffraction, H2 temperature programmed reduction and X-ray photoelectron spectroscopy. The catalytic activity was greatly influenced by ZnO contents in Zr0.5Al0.5O1.75 support. The catalyst containing 15% ZnO exhibited a light-off temperature and complete conversion temperature for CH4 in the absence of H2O of 278 and 314 °C, respectively; while these same values in the presence of H2O were 342 and 371 °C, respectively. These results indicate that this combination of materials offers excellent catalytic activity at low temperature and also exhibits significant H2O tolerance.