The effect of CeO 2 and BaO on Pd catalysts used for lean-burn natural gas vehicles

Abstract

Palladium catalysts supported on Al 2O 3 doped by BaO and/or CeO 2 were prepared by impregnation method. Various techniques, including N 2 adsorption (Brunauer–Emmet–Teller method; BET), X-ray diffraction (XRD), CO-chemisorption, H 2-temperature-programmed reduction (H 2-TPR) and X-ray photoelectron spectroscopy (XPS), were employed to characterize the effect of BaO and/or CeO 2 on the physicochemical properties of prepared catalysts. Catalytic activities for methane and CO oxidation were evaluated in a gas mixture simulated the exhaust from lean-burn natural gas vehicles (NGVs) . The BET results showed that the supports possessed high specific surface area, suitable pore volume and pore size distribution. The activity results indicated that the catalyst modified by CeO 2 showed the best performance for methane and CO removal, and the one modified by both BaO and CeO 2 the worst. CO-chemisorption and H 2-TPR results indicated that the addition of ceria or barium alone could increase the dispersion of palladium and improve the reducibility of catalysts. The results of XPS showed that BaO increased the electron density around PdO while CeO 2 activated the lattice oxygen and increased the content of oxygen species on the surface of catalysts. When BaO and CeO 2 were added simultaneously, their respective potential effect was restrained by each other resulting in the decrease of catalytic activity.