Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO_2.8H_0.2 Catalyst for CO₂ Hydrogenation to Methanol

Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal-support interactions when using supported metal nanoparticles. This study focuses on CO₂ hydrogenation over supported Cu nanoparticles, revealing a 3-fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO_2.8H_0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO₃ yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO_2.8H_0.2 surface hydride species follow a Mars van Krevelen mechanism in CO₂ hydrogenation, promoting methanol production. High-pressure steady-state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO_2.8H_0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO₃. An operando high-pressure diffuse reflectance infrared spectroscopy (DRIFTS)-SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate-limiting. However, the catalytic reactivity of Cu/BaTiO_2.8H_0.2 towards the formate species is much higher than Cu/BaTiO₃, likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.