Hydroxyl-oxygen vacancy synergy over In2O3–ZrO2 catalysts: mechanistic insights into CO2 hydrogenation to methanol

Abstract

The synergistic interplay between oxygen vacancies (O_V) and hydroxyl species in In₂O₃–ZrO₂ catalysts plays a crucial role in steering CO₂ hydrogenation pathways, however, the atomic-scale interactions between these features have remained elusive. In this study, we engineered In₂O₃–ZrO₂ solid solutions via ZrO₂ aerogel phase modulation and thoroughly elucidated the surface chemistry using advanced experimental techniques, including solid-state NMR, in situ DRIFTS, and adsorption studies. The results demonstrate that three distinct hydroxyl site types on the catalyst's surface (terminal hydroxyls (μ₁-OH), bridged hydroxyls (μ₂-OH), and triply bridging hydroxyls (μ₃-OH)) are in close spatial proximity. Besides, μ₂-OH and μ₃-OH are particularly susceptible to dihydroxylation, a process that facilitates the generation of O_V that serve as anchoring sites for CO₂. These hydroxyl-vacancy ensembles effectively promote CO₂ activation to carbonate/bicarbonate species, which then undergo selective hydrogenation to methanol via a formate-mediated pathway, thus establishing a self-sustaining catalytic cycle. This work clarifies the cooperative role of vacancy coordination and hydroxyl chemistry in CO₂ activation and provides a mechanistic guide for the rational design of bimetallic oxide catalysts for CO₂ hydrogenation to methanol.