(407e) Structure-Activity Relationships of Metal Oxide/Cu-Based Catalysts for CO2 Hydrogenation to Methanol

CO₂ hydrogenation to methanol using renewable H₂ is a promising strategy to mitigate global warming and an efficient way for renewable chemical production. Metal oxide/Cu-based catalysts (e.g., ZrO₂/Cu, ZnO/Cu, etc.) are promising systems for this reaction, while the nature of the active sites and their structure-activity relationships remains debatable.¹

In this work, we showcase two model catalyst systems to investigate the structure-activity relationships in CO₂ hydrogenation reaction: (1) inverse ZrO₂/Cu (Cu particle size: 20-40 nm) synthesized via a sol-gel method, and (2) ZnO/Cu/SiO₂ with uniform Cu nanocrystals (~7nm) made by colloidal chemistry and controllable ZnO layers prepared by atomic layer deposition (ALD)²). In both systems, metal oxides significantly enhance the methanol formation rates compared to bare Cu catalysts, which predominantly yield CO. For the inverse ZrO₂/Cu catalysts, we identified that under reductive conditions, Cu species beneath the ZrO₂ overlayer are highly dynamic, migrating to the outer surface of the ZrO₂ overlayer and forming Cu nanoclusters. This restructuring behavior was tracked using Environmental TEM (Fig. 1a). In the ZnO/Cu/SiO₂ system, we found that encapsulating Cu/SiO₂ by ZnO ALD layers enhanced both CO₂ conversion and methanol selectivity compared to Cu deposited on ZnO-modified SiO₂ (Fig. 1b). In particular, the methanol selectivity increased from ~50% to ~80%, suggesting the original configuration of ZnO/Cu plays a key role in catalytic performance. In-situ DRIFTS and DFT calculation suggest that CO₂ hydrogenation to methanol over both catalyst systems likely proceeds via the formate reaction pathway with CO₂ activates on the Cu-metal oxide interface, and H₂ activation on the surface of Cu facilitating the further hydrogenation of carbonate/bicarbonate.

1. Chem. Rev. 2024, 124, 8, 4543–4678.
2. ChemCatChem 2021, 13, 770-781.