Hydrogen spillover effect in CO2 hydrogenation: modulations, characterization and applications

The hydrogenation of carbon dioxide to produce high-value chemicals, such as methane and methanol, is one of the most effective methods to mitigate the greenhouse effect, offering both ecological and economic benefits. In traditional hydrogenation reactions, hydrogen spillover is a common phenomenon. It refers to the migration of hydrogen atoms between active sites after the dissociation of hydrogen molecules, facilitating further hydrogenation reactions. This process has widespread applications in catalytic hydrogenation and hydrogen storage. However, the role of the hydrogen spillover effect in CO2 hydrogenation has not yet been systematically reviewed or summarized. This review first briefly summarizes the hydrogen spillover mechanisms on various types of supports, including reducible supports, non-reducible supports, carbon materials, and metal-organic frameworks (MOFs). Subsequently, the strategies for modulating hydrogen spillover and the characterization methods are systematically discussed. Lastly, the review focuses on the application of the hydrogen spillover effect in CO2 hydrogenation reactions, explaining how controlling the hydrogen spillover can enhance catalytic performance and even overturn product selectivity. In particular, the review also highlights the potential role of hydrogen spillover in integrated CO2 capture and utilization systems. Finally, the challenges and limitations in hydrogen spillover research are discussed, providing insights for a deeper understanding and future application of this phenomenon.