Dopant-controlled oxygen vacancy dynamics define CO₂-to-methanol catalysis on In₂O₃

Abstract

Controlling the intrinsic activity and long-term stability of active sites is essential to advance the formulation of catalysts. The hydrogenation of CO₂ to methanol over indium oxide (In₂O₃) is believed to proceed at oxygen vacancies (V_O^∙∙) formed in situ. Here, we study how the structural dynamics of c-In₂O₃ are altered through doping with Sn or Zr, affecting the local structure, catalytic activity, and stability. We find that V_O^∙∙ sites in Sn-doped c-In₂O₃ are unreactive towards their replenishment by CO₂, leading to catalyst deactivation by the formation of In⁰ and Sn⁰. Conversely, V_O^∙∙ sites in Zr-doped c-In₂O₃ show a high reactivity towards CO₂, translating into a high catalytic activity and stability against over-reduction-induced deactivation. The diverging properties originate from the distinct defect dynamics in these two materials. The balance between V_O^∙∙ formation and its replenishment during CO₂ hydrogenation is the key characteristic for both activity and stability of In₂O₃-based catalysts.