Hydrogenation Reaction on Pd-Cu Bimetallic Catalysts: A Parahydrogen-Induced Polarization Study

Abstract

Hydrogenation reaction of propyne on Pd-Cu bimetallic catalysts was studied using the heterogeneous parahydrogen-induced polarization (PHIP) nuclear magnetic resonance (NMR) technique. Incipient-wetness impregnation and sequential impregnation were used to prepare Pd-Cu/SiO2 bimetallic catalysts with different composition and morphology. With the ALTADENA (Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment) method, it was observed that both the composition and morphology of the bimetallic catalysts had significant influence on the efficiency of PHIP. The catalysts with lower Pd/Cu atom ratio had lower activity but higher polarization efficiency. Compared to isometric impregnation method, the palladium atoms in the Pd-Cu/SiO2 catalyst synthesized with the sequential impregnation method mostly stayed on the surface of bimetallic nanoparticles, generating larger Pd ensembles and leading to higher catalytic activity and lower polarization efficiency.

Keywords

• parahydrogen-induced polarization (PHIP)
• bimetallic catalyst
• propyne hydrogenation reaction
• signal intensity enhancement
• nuclear magnetic resonance (NMR)