Targeted Formation of Bidentate Carbonates at Alkaline Sites for Efficient CO₂ Photomethanation

Precise design of active sites is crucial for developing highly efficient and selective catalysts. However, in CO₂ conversion, the lack of systematic evaluation of CO₂ promoters and more importantly the atomic-level understanding of their interactions has limited the continuous progress of CO₂-conversion catalysts. Here, we present a CoAl oxide modified with tailored functional sites and employ CO₂ photomethanation as a model reaction to probe the interactions between reactants and active sites. Specifically, experimental and theoretical results elucidate that the promotion effects of alkaline sites (Li, Na, K, and Cs) originate from their ability to activate CO₂ into effective species of bidentate carbonates (b-CO₃*). Meanwhile, the introduced Ru species enable the heterolytic H₂ dissociation and the as-formed H^δ- species, then efficiently drive the successive hydrogenation of b-CO₃* intermediates into CH₄. Based on this targeted activation of CO₂ into b-CO₃* (and H₂ into H^δ-), the catalyst delivers an excellent single-pass CO₂ conversion of ∼77% and CH₄ selectivity of ∼97.7% at a WHSV of 30,000 mL g_cat ^-1 h^-1 (2.6 W cm^-2 irradiation), with stable operation for nearly 400 h. This work provides valuable insights into targeted activation of CO₂ and offers a new perspective for CO₂ conversion into value-added chemicals.