CO₂ Hydrogenation to Methanol over In₂O₃-Based Catalysts: From Mechanism to Catalyst Development

Abstract

Carbon dioxide (CO2) hydrogenation to methanol with H2 produced with renewable energy represents a promising path for the effective utilization of a major anthropogenic greenhouse gas, in which catalysts play a key role for CO2 conversion and methanol selectivity. Although still under development, indium oxide (In2O3)-based catalysts have attracted great attention in recent years due to the excellent selectivity to methanol along with high activity for CO2 conversion. In this review, we discuss recent advances of In2O3-based catalysts for CO2 hydrogenation based on both experimental and computational studies. Various strategies have been adopted to improve the catalytic performance by facilitating the formation of surface oxygen vacancies (In2O3–x) as active sites, the activation of CO2 and H2 toward hydrogenation to methanol to mitigate reverse water–gas shift reaction, and the stabilization of the key intermediates. Mechanistic insights are gained from combining catalytic kinetic studies, in situ characterization, and theoretical investigations involving CO2 conversion via the formate HCOO* pathway versus the carboxyl COOH* pathway. Strategies to further promote selective CO2 hydrogenation to methanol include adding a metal component such as Pd or Ni on In2O3 (which may also involve formation of bimetallic In–M catalysts) to promote H2 activation and oxygen vacancy formation, combining In2O3 with an oxide promoter such as ZrO2 to enhance CO2 adsorption and activation, controlling the concentration of CO and H2O to enhance methanol formation, and adopting a second catalytic component to enhance CO2 conversion to other desired products such as olefins or aromatics on an acid catalyst such as zeolites. Through a comprehensive overview of the recent advances in In2O3-related catalysts, the present review paves the way for future development in In2O3-based selective catalysts for CO2 hydrogenation to methanol.