Methanol Synthesis from CO2 over ZnO-Pd/TiO2 Catalysts: Effect of Pd Precursors on the Formation of ZnPd-ZnO Active Sites

Abstract

This study examines the factors influencing the formation and structure of ZnPd-ZnO active sites supported on TiO2 by comparing their genesis from Pd/TiO2 base catalysts prepared by impregnation using different Pd precursors (Pd(NH3)4(NO3)2 and Pd(acac)2). The experimental results demonstrated that, in contrast to the production of CO over Pd/TiO2 base catalysts, the selectivity of methanol over ZnPd-ZnO/TiO2 catalysts was significantly affected by the dispersion of ZnPd intermetallic particles and the development of ZnPd-ZnO interfaces. These are determined by the characteristics of Pd particles supported on TiO2 and their contact with the ZnO particles deposited on them. The Pd/TiO2 base catalyst prepared by impregnation with neutral Pd precursor (Pd(acac)2) produces a higher concentration and more effective dispersion of the ZnPd intermetallic phase as well as a wider ZnO-ZnPd interface region in comparison to the Pd/TiO2 counterpart synthetized using the cationic Pd precursor (Pd(NH3)4(NO3)2). These differences in the ZnPd-ZnO active sites resulted in notable variations in the methanol yield, achieving the catalysts prepared with the neutral precursor about twice higher methanol selectivity from CO2 hydrogenation at low temperatures.