Mechanistic Studies of Methanol Synthesis Reaction over Cu and Pd–Cu Catalysts

Abstract

Monometallic copper and bimetallic palladium–copper catalysts supported on ZnO–Al₂O₃, CeO₂–Al₂O₃ and ZrO₂–Al₂O₃ were prepared by conventional impregnation method and tested in the methanol synthesis reaction in a gradient less reactor under elevated pressure (3.5 MPa) at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, TPR-H₂, TPD-NH₃, XRD, SEM-EDS and FT-IR techniques. The results of XRD and SEM-EDS measurements showed the formation of Pd–Cu alloy during the activation of bimetallic catalysts. It was found that the formed alloy was responsible for the improved activity and selectivity of catalysts in the studied reaction. Among investigated catalysts, the highest formation rate of methanol was observed with 2%Pd–20%Cu/ZnO–Al₂O₃ system. Based on the results of FT-IR measurements it can be concluded that hydrogen molecules adsorb dissociatively on the metallic copper surface to form hydrogen atoms, increasing the hydrogen spillover effect on the metal-support interface. In contrast, CO₂ adsorb on the oxygen vacancies of the support to form carbonates, which can further undergo hydrogenation to methanol.