Engineered Chemical Utilization of CO2 to Methanol via Direct and Indirect Hydrogenation Pathways: A Review

Nowadays, more than 80% of the world's energy supply is provided by nonrenewable fossil fuels (oil, coal, and natural gas), which are the main sources of CO2 emission. The conversion of CO2 into the most useful organic chemicals (methanol and ethylene glycol (EG)) not only effectively mitigates CO2 emissions but also produces value-added chemicals and replaces nonrenewable energy sources. This Review provides a comprehensive view of the significant research progress on indirect CO2 hydrogenation to methanol and EG through the ethylene carbonate intermediate. First, the advances and challenges of direct catalytic hydrogenation of CO2 to methanol are addressed. Subsequently, the advances in CO2 epoxidation to cyclic carbonates, particularly to ethylene carbonate, are summarized. This matured and commercialized ethylene carbonate (EC) production route is vital because of the efficient production of EG and methanol from catalytic hydrogenation of EC and hydrolysis of EC to EG, which replaces the conventional EG production process by hydration of ethylene oxide. Then, the progress on the catalytic hydrogenation of CO2-derived EC is discussed in detail, focusing on Cu-based heterogeneous catalysts. We provided a detailed discussion with emphasis on the nature, evolution, and precise role of active sites in Cu-based catalysts, including other influencing factors such as the preparation method, support, and addition of promoters. Moreover, the possible hydrogenation reaction mechanism, reaction conditions, design optimization, and on-site assessment of Cu-based catalysts for EC hydrogenation are included. Lastly, we provided a summary and outlook.