Unraveling Reaction Pathways in CO2 Hydrogenation to Methanol at Metal-Oxide Interfaces

Abstract

The efficiency of methanol synthesis from CO₂ hydrogenation is primarily governed by the metal/oxide interface of the catalyst. Identifying active interfaces and their associated reaction pathways is therefore a crucial objective in catalyst design. We here report the use of well-defined Pd nanocrystals to produce catalysts for systematically investigating the impact of metal/oxide interfaces on CO₂ hydrogenation. Catalytic measurements revealed substantial variations in activity across different metal/oxide interfaces, with Pd supported on reducible oxides (TiO₂, CeO₂, and In₂O₃) exhibiting significantly higher activity than Pd on nonreducible supports (SiO₂ and Al₂O₃). Methanol selectivity also varied notably, with Pd/In₂O₃ achieving a methanol selectivity of 95%, far exceeding the performance of other Pd catalysts (below 45%). Experimental and DFT results showed that Pd/In₂O₃ facilitates the direct hydrogenation of CO₂ to methanol via a formate-intermediate pathway, whereas Pd/TiO₂ and Pd/CeO₂ proceed through dual pathways involving both formate and CO intermediates. These distinctions in reaction pathways stem from the nature of Pd–metal oxide interfacial sites and the presence of oxygen vacancies. These findings highlight the critical role of metal/oxide interfaces in dictating reaction pathways and controlling methanol productivity during CO₂ hydrogenation, offering valuable insights for designing efficient catalysts for methanol production from CO₂.