Acid site-assisted vapor-phase oxidation of ethene to acetic acid over palladium with silica-supported tungstosilicic acid and tungstated zirconia Original Research Article

The selective oxidation of ethene to acetic acid in the vapor phase over solid acid-supported Pd catalyst was investigated to elucidate the reaction mechanism and the roles of Pd and acidic sites in promoting the reaction. Two catalysts, Pd–H4SiW12O40/SiO2 and Pd/WO3–ZrO2, exhibited high catalytic activity. Variations in product distribution with contact time, the requirement for the presence of water vapor for the reaction to occur, and the reactivities of possible reaction intermediates indicated that acetic acid is formed via an acetaldehyde intermediate which is produced in a Wacker-type reaction, while the role of the acid sites is to re-oxidize Pd0 into Pd2+ in the presence of O2. It was concluded that catalytic efficiency is dependent on maximization of the interface between metallic Pd and acidic surface by establishing an appropriate ratio of Pd and acidic sites.