Insights into syngas to methanol conversion on Cr₂O₃ oxide from first-principles-based microkinetic simulations^†

Cr₂O₃ has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate, e.g., methanol, from syngas. By combining density functional theory calculations and microkinetic modeling, we computationally studied the surface structures and catalytic activities of bare Cr₂O₃ (001) and (012) surfaces, and two reduced (012) surfaces covered with dissociative hydrogens or oxygen vacancies. The reduction of (001) surface is much more difficult than that of (012) surface. The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion, and the hydrogenation of CO or CHO is identified as rate-determining step. Microkinetic modeling reveals that (001) surface is inactive for the reaction, and the rates of both reduced (012) surfaces (25−28 s⁻¹) are about five times higher than bare (012) surface (4.3 s⁻¹) at 673 K. These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis.