Transformation of Alumina-Supported Palladium Precursors during Reductive Activation

Abstract

The transformation of alumina-supported palladium salts during isothermal treatment in a reducing atmosphere has been studied to determine the optimum reduction temperature for the Pd/Al₂O₃ catalyst. It has been found that the interaction of palladium acetylacetonate with alumina surface sites is stronger than the interaction of the acetate complex. Owing to this factor, the diameter of the resulting active-ingredient particles is smaller in the case of the former precursor in the entire temperature range of reductive treatments. The optimum reduction temperature for the supported palladium salts is 500°С; this temperature provides the formation of palladium particles characterized by the maximum conversion of methylacetylene and propadiene at a high selectivity for conversion to propylene. The systems activated at temperatures of up to 400°C exhibit low activity in the hydrogenation of methylacetylene and propadiene; this behavior is attributed to an incomplete reduction of palladium from Pd salts to form oxidized and coordinatively unsaturated species of the active ingredient.