Dynamic Zn-Based Ensembles Govern CO2 Hydrogenation to Methanol on Cu/ZnO/Al2O3 Catalyst

Abstract

The active site of the classical Cu/ZnO/Al2O3 (CZA) catalyst for CO2 hydrogenation remains elusive as its surface structures undergo dynamic change under reaction conditions. Here, we combine neural network interatomic potential molecular dynamics simulations and grand-canonical density functional theory calculations to investigate the evolution of the representative CuZn alloy and inverse ZnO/Cu surface phases, and we consistently observe drastic restructuring under hydrogenation conditions, forming fragmented Zn-based ensembles at Cu support. Among the pathways examined, CO2 hydrogenation on these ensembles preferentially proceeds through the HCOO pathway, with different ensemble compositions being thermodynamically favored for the intermediates formed at different reaction stages. Importantly, these Zn-based ensembles are highly dynamic on Cu, allowing the inert HCOO within the ensembles to access highly active Cu/Zn interfacial sites, thereby making its hydrogenation kinetically accessible. The formation of ensembles and their dynamic behavior may be related to a suitable Cu–Zn interaction, which stabilizes Zn on Cu while preserving its mobility. Overall, these findings identify dynamic Zn-based ensembles as potential operando active sites in the Cu–Zn component of CZA and show that catalyst restructuring not only changes surface morphology but also couples directly to the reaction mechanism.