Excellent complete conversion activity for methane and CO of Pd/TiO2-Zr0.5Al0.5O1.75 catalyst used in lean-burn natural gas vehicles

Palladium catalysts are supported on TiO₂, ZrO₂, Al₂O₃, Zr_0.5Al_0.5O_1.75 and TiO₂-Zr_0.5Al_0.5O_1.75 prepared by co-precipitation method, respectively. Catalytic activities for methane and CO oxidation are evaluated in a gas mixture that simulated the exhaust from lean-burn natural gas vehicles (NGVs). Pd/TiO₂-Zr_0.5Al_0.5O_1.75 performs the best catalytic activity among the tested five catalysts. For CH₄, the light-off temperature (T₅₀) is 254 °C, and the complete conversion temperature (T₉₀) is 280 °C; for CO, T₅₀ is 84 °C, and T₉₀ was 96 °C. Various techniques, including N₂ adsorption-desorption, X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) are employed to characterize the effect of supports on the physicochemical properties of prepared catalysts. N₂ adsorption-desorption and SEM show that TiO₂-Zr_0.5Al_0.5O_1.75 expresses uniform nano-particles and large meso-pore diameters of 26 nm. H₂-TPR and XRD indicate that PdO is well dispersed on the supports and strongly interacted with each other. The results of XPS show that the electron density around PdO and the proportion of active oxygen on TiO₂-Zr_0.5Al_0.5O_1.75 are maxima among the five supports.