Computational Insights into Alloying and Confinement Effects on Promoted Activity and Selectivity of C₂ Oxygenate over Rh-Based Catalysts

Abstract

Improving both activity and selectivity of C2 oxygenate (C2-oxy) over Rh catalysts is challenging. Experimental results have shown that the C2-oxy yield over pure Rh catalysts can be greatly promoted by the combined effects of alloying (Mn promotor) and confinement. Combining density functional theory calculations and microkinetic simulations, we have revealed that the formed Rh–Mn reaction site breaks the scaling relationship between the adsorption energies of intermediates, resulting in a new CO activation path and the stabilization of C2 intermediates, which can improve not only the CO conversion activity but also the C2-oxy selectivity. On the basis of the alloying effect, the confinement effect can further break the scaling relationship between the adsorption energies of intermediates, which can selectively suppress the formation of some useless but abundant species. This leads to the improved effects for the coverage of key intermediates. As a result, the CO conversion activity is further facilitated without the decrease of C2-oxy selectivity. Therefore, the C2-oxy yield can be enhanced. However, without the Mn promotor, the confinement effect alone can only slightly improve the CO conversion activity with poor C2-oxy selectivity. The insights herein regarding the synergistic effects with alloying and confinement are of great significance to regulate the activity and selectivity of C2-oxy in syngas conversion.