Size-dependent strong metal–support interaction in Pd/ZnO catalysts for hydrogenation of CO2 to methanol

Abstract

Strong metal–support interaction (SMSI) has long been studied in catalytic reactions. Proper utilization of the SMSI effect might not only improve the stability of the catalysts, but also the activity and selectivity. In this work, using the atomic layer deposition (ALD) technique, we synthesized a series of Pd/ZnO catalysts with Pd particle sizes ranging from 1.6 to 7.9 nm. Upon H₂ reduction at elevated temperatures, these Pd/ZnO catalysts display a size-dependent SMSI effect wherein the larger-size Pd particles are more prone to be encapsulated by ZnO compared to the smaller ones. In the reaction of CO₂ hydrogenation, we show that such size-dependent SMSI, together with the size-related CO binding strength on Pd particles, provides a higher activity and methanol selectivity to the Pd particles larger than ~2.5 nm.