The effect of CeO2 and BaO on Pd catalysts used for lean-burn natural gas vehicles

Palladium catalysts supported on Al2O3 doped by BaO and/or CeO2 were prepared by impregnation method. Various techniques, including N2 adsorption (Brunauer–Emmet–Teller method; BET), X-ray diffraction (XRD), CO-chemisorption, H2-temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS), were employed to characterize the effect of BaO and/or CeO2 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 CeO2 showed the best performance for methane and CO removal, and the one modified by both BaO and CeO2 the worst. CO-chemisorption and H2-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 CeO2 activated the lattice oxygen and increased the content of oxygen species on the surface of catalysts. When BaO and CeO2 were added simultaneously, their respective potential effect was restrained by each other resulting in the decrease of catalytic activity.

Graphical abstractAl2O3 supports doped by CeO2 and/or BaO and Pd catalysts are prepared and characterized. Catalytic activities are investigated in a mixture gas simulated the exhaust emissions from lean-burn natural gas vehicles (NGVs). The doping of CeO2 or BaO alone can increase catalytic activity for methane and CO oxidation, however, the coexistence of CeO2 and BaO causes detrimental effect to activity.Figure optionsDownload full-size imageDownload as PowerPoint slide