Role of H₂O in Catalytic Conversion of C₁ Molecules

Due to their role in controlling global climate change, the selective conversion of C₁ molecules such as CH₄, CO, and CO₂ has attracted widespread attention. Typically, H₂O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H₂O can also participate in the catalytic conversion of C₁ molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H₂O-mediated conversion of C₁ molecules. We aim to provide an in-depth and systematic understanding of H₂O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H₂O on the reactions of C₁ molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H₂O-mediated catalytic conversion of C₁ molecules.