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

Abstract

The synergistic interplay between oxygen vacancies (OV) 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 OV 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.