Cesium-Induced Active Sites for C-C Coupling and Ethanol Synthesis from CO2 Hydrogenation on Cu/ZnO(0001̅) Surfaces.

Abstract

The efficient conversion of carbon dioxide, a major air pollutant, into ethanol or higher alcohols is a big challenge in heterogeneous catalysis, generating great interest in both basic scientific research and commercial applications. Here, we report the facilitated methanol synthesis and the enabled ethanol synthesis from carbon dioxide hydrogenation on a catalyst generated by codepositing Cs and Cu on a ZnO(0001̅) substrate. A combination of catalytic testing, X-ray photoelectron spectroscopy (XPS) measurements, and calculations based on density functional theory (DFT) and kinetic Monte Carlo (KMC) simulation was used. The results of XPS showed a clear change in the reaction mechanism when going from Cs/Cu(111) to a Cs/Cu/ZnO(0001̅) catalyst. The Cs-promoting effect on C-C coupling is a result of a synergy among Cs, Cu, and ZnO components that leads to the presence of CHx and CHyO species on the surface. According to the DFT-based KMC simulations, the deposition of Cs introduces multifunctional sites with a unique structure at the Cu-Cs-ZnO interface, particularly being able to promote the interaction with CO2 and thus the methanol synthesis predominantly via the formate pathway. More importantly, it tunes the CHO binding strongly enough to facilitate the HCOOH decomposition to CHO via the formate pathway, but weakly enough to allow further hydrogenation to methanol. The fine-tuning of CHO binding also enables a close alignment of a CHO pair to facilitate the C-C coupling and eventually ethanol synthesis. Our study opens new possibilities to allow the highly active and selective conversion of carbon dioxide to higher alcohols on widely used and low-cost Cu-based catalysts.