Preserving the Active Cu–ZnO Interface for Selective Hydrogenation of CO₂ to Dimethyl Ether and Methanol

Abstract

It is of importance but highly challenging for copper (Cu)-based catalysts to maintain the structure of active Cu sites under working conditions. Herein, the commercial Cu/ZnO/Al2O3 catalyst was confined in the mesoporous SiO2–Al2O3 shell via hydrothermal synthesis (CZAS@SA) for selective hydrogenation of CO2 to dimethyl ether (DME) and methanol. CZAS@SA catalysts exhibited higher intrinsic activity for the formation of DME and methanol and much lower intrinsic activity for CO formation than Cu/ZnO/Al2O3. Thus, the total selectivity of DME and methanol was enhanced from 9.1 to 63.3 mol %. In situ X-ray photoelectron spectroscopy/X-ray absorption fine structure/high-resolution transmission electron microscopy (XPS/XAFS/HRTEM) results and catalytic measurements indicated that the metallic Cu(Cu0)–ZnO interface was the active site for methanol formation. Commercial Cu/ZnO/Al2O3 underwent a separation of Cu0 and ZnO phases during the reaction, and this phase separation caused agglomeration of Cu0 and shrinking of the active Cu0–ZnO interface, which aggregated CO formation. The active Cu0–ZnO interface in CZAS@SA was preserved due to the confinement effect of the shell, which improved methanol selectivity.