Importance of metal-polymer interface for chemoselectivity on Pd supported on S-containing polymer

Abstract

Partial hydrogenation of alkyne is one of the important reactions in chemical industry. Many catalysts with organic modifiers showed high selectivity of alkene at the expense of catalytic activity and stability. In the present work, we successfully synthesized stable palladium catalyst supported on the sulfur-containing polymer with both high catalytic activity and selectivity. To identify the unique mechanism for chemoselectivity and the interfacial interaction between metal and the polymer, two catalysts with different positions of metal in the polymer were prepared. We prepared catalysts with metal embedded inside the polymer by the conventional wetness impregnation, and catalysts with the metal located on the polymer surface by adsorption of premade nanoparticles. Interfacial interaction between metal and sulfur moiety on the polymer enabled selective adsorption of alkyne over alkene regardless of metal position. Discriminate adsorption of alkyne resulted in high alkene selectivity (>85%) in various alkyne hydrogenation reactions. Metal located on the surface of the polymer enabled to easily access to reactants than metal located inside the polymer. High accessibility to metal allowed twice-higher catalytic turnover. The combination effect of strong interaction with sulfur on the polymer and easily accessible location of metal enhanced both chemoselectivity and catalytic activity. Our research suggests the possibility of designing optimal catalyst with both high catalytic activity and selectivity by understanding the properties of polymer.