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

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.