Synthesis and characterization of sol–gel zirconia supported Pd and Ni catalysts

Sol–gel Ni and Pd supported ZrO2 catalysts have been synthesized by the sol–gel method, characterized and their catalytic activity examined for dichloromethane (DCM) oxidation. Acid hydrolysis of zirconium alkoxide supports was performed with H2SO4 or HNO3 in order to compare the catalytic properties of prepared catalysts. Two methods were used to introduce Pd and Ni, namely cogellation and impregnation. In the first method the metal precursor was introduced into the initial solution while in the impregnated samples the metal was spread over the carrier surface. The physicochemical properties of catalysts were investigated using conventional characterization methods. Under reaction conditions sulfate species remain onto the catalyst surface giving rise to acid Brönsted sites that favor the extraction of Cl atoms from DCM molecule. A bifunctional mechanism in which the metallic phase is required for burning-off coke produced over the support surface is proposed. Only impregnated catalysts are effective in the oxidation of DCM since the metallic phase is buried into support particles when catalysts are prepared by cogellation method.