Exploring catalyst developments in heterogeneous CO2 hydrogenation to methanol and ethanol: A journey through reaction pathways

The pursuit of alternative fuel generation technologies has gained momentum due to the diminishing reserves of fossil fuels and global warming from increased CO2 emission. Among the proposed methods, the hydrogenation of CO2 to produce marketable carbon-based products like methanol and ethanol is a practical approach that offers great potential to reduce CO2 emissions. Although significant volumes of methanol are currently produced from CO2, developing highly efficient and stable catalysts is crucial for further enhancing conversion and selectivity, thereby reducing process costs. An in-depth examination of the differences and similarities in the reaction pathways for methanol and ethanol production highlights the key factors that drive C–C coupling. Identifying these factors guides us toward developing more effective catalysts for ethanol synthesis. In this paper, we explore how different catalysts, through the production of various intermediates, can initiate the synthesis of methanol or ethanol. The catalytic mechanisms proposed by spectroscopic techniques and theoretical calculations, including operando X-ray methods, FTIR analysis, and DFT calculations, are summarized and presented. The following discussion explores the structural properties and composition of catalysts that influence C–C coupling and optimize the conversion rate of CO2 into ethanol. Lastly, the review examines recent catalysts employed for selective methanol and ethanol production, focusing on single-atom catalysts.