Preparation and Characterization of Covalent Organic Polymer Supported Palladium Catalysts for Oxidation of CO and Benzyl Alcohol

A novel covalent organic polymer, COP-4, with high thermal stability and large surface area, was used as the support to prepare Pd/COP-4 catalyst using conventional impregnation and hydrogen reduction. The obtained catalyst shows excellent activity for oxidation reactions in gas-phase (CO oxidation) and liquid-phase (oxidation of benzyl alcohol to benzaldehyde). The solvent-free aerobic oxidation of benzyl alcohol to benzaldehyde without any base was examined for the first time. The catalyst characterization indicates that the solvent used in the impregnation has an influence on the interaction between the active metal particle and the support. Different solvent results in different catalytic property. For Pd/COP-4 prepared with distilled water, it tends to physically adsorb many more CO molecules on the surface. This would be the reason that this catalyst has better activity for CO oxidation. The Pd/COP-4 catalyst prepared in DMF has a much larger surface area, smaller average particle size, and broader size distribution. It shows better activity and worse selectivity for selective oxidation of benzyl alcohol to benzaldehyde.