Investigation of different catalytic behaviors of Pd single atoms and nanoparticles on sulfur-containing polymer support

Abstract

Partial hydrogenation of alkynes to alkenes is an important catalytic process in various industry and also key model reaction for fundamental investigation of chemoselectivity in heterogeneous catalysis. Polymer supported catalysts have attracted increasing attention as a means of achieving enhanced activity, selectivity, and stability. However, coexistence of Pd single atoms and nanoparticles on the supports made the systematic investigation of the catalysts difficult. In this research, we successfully synthesized two catalysts where either Pd single atoms or nanoparticles are selectively formulated on the polymer supports. When heat is provided, both Pd atoms and nanoparticles are embedded into polymer network via dynamic motions of the polymer chains. Pd nanoparticles show much higher catalytic activity than single atoms in acetylene partial hydrogenation. Polymer chains surrounding Pd nanoparticles act as a ‘molecular gate’ which enables discriminative adsorption and hydrogenation of alkyne over alkene, resulting in high alkene selectivity. The enhanced alkene selectivity and initial conversion of the polymer supported nanoparticles were retained over a long reaction period, which is speculated to be due to an immediate removal of coke precursor from Pd surface by the polymer chains.