CO 2 Hydrogenation to Methanol over In 2 O 3 -Based Catalysts: From Mechanism to Catalyst Development

Carbon dioxide (CO 2 ) hydrogenation to methanol with H 2 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 CO 2 conversion and methanol selectivity. Although still under development, indium oxide (In 2 O 3 )-based catalysts have attracted great attention in recent years due to the excellent selectivity to methanol along with high activity for CO 2 conversion. In this review, we discuss recent advances of In 2 O 3 -based catalysts for CO 2 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 (In 2 O 3– x ) as active sites, the activation of CO 2 and H 2 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 CO 2 conversion via the formate HCOO* pathway versus the carboxyl COOH* pathway. Strategies to further promote selective CO 2 hydrogenation to methanol include adding a metal component such as Pd or Ni on In 2 O 3 (which may also involve formation of bimetallic In–M catalysts) to promote H 2 activation and oxygen vacancy formation, combining In 2 O 3 with an oxide promoter such as ZrO 2 to enhance CO 2 adsorption and activation, controlling the concentration of CO and H 2 O to enhance methanol formation, and adopting a second catalytic component to enhance CO 2 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 In 2 O 3 -related catalysts, the present review paves the way for future development in In 2 O 3 -based selective catalysts for CO 2 hydrogenation to methanol.