Effects of ZrO2/Al2O3 properties on the catalytic activity of Pd catalysts for methane combustion and CO oxidation

Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO2/Al2O3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO3)2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO2 is highly dispersed on the surface of Al2O3 up to 10 wt.% ZrO2, beyond this value tetragonal ZrO2 is formed. The presence of a small amount of ZrO2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO2, but it does not accelerate the activity of 0.2% Pd/ZrO2/Al2O3 for methane combustion. 0.2% Pd/ZrO2/Al2O3 dried at 120 °C shows highest activity for CH4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH4 combustion.