Mechanistic Insights into Structure-Driven Selectivity in CO2 Hydrogenation Over Cu-Based Catalysts

Abstract

Recent experiments indicate that the methanol selectivity in the CO2 hydrogenation to methanol on copper is sensitive toward the catalyst structure, yet the mechanistic origins of such an effect remain unclear. In this study, we employ DFT calculations and statistical thermodynamics to elucidate the role of different copper catalyst facets in governing the product selectivity toward CO or methanol. Our analysis shows that both MeOH and rWGS reactions are structure-sensitive, agreeing with UHV experiments on clean copper surfaces. More interestingly, our study reveals that the competition between the two catalytic cycles is dependent on the catalyst structure: Cu(110) promotes methanol formation via a formate-mediated mechanism without any CO*-based intermediates, while Cu(111) favors CO formation via a newly proposed formate-to-carboxyl isomerization route. This distinction arises from the different activation tendencies of the key HCOOH* surface intermediate on each surface, driven by different adsorbate and transition-state stabilization effects. Our findings rationalize the experimental observations by supporting the hypothesis that different Cu facets exhibit a strong propensity toward enabling distinct catalytic cycles, leading to different product formation on them. As such, this work highlights the importance of accounting for structural information in the microkinetic analysis of CO2 hydrogenation pathways.