The superiority of Pd²⁺ in CO₂ hydrogenation to formic acid

The hydrogenation of CO₂ to formic acid is an essential subject since formic acid is a promising hydrogen storage material and a valuable commodity chemical. In this study, we report for the first time the hydrogenation of CO₂ to formic acid catalyzed by a Pd²⁺ catalyst, Pd-V/AC-air. The catalyst exhibited extraordinary catalytic activity toward the hydrogenation of CO₂ to formic acid. The TON and TOF are up to 4790 and 2825 h^-1, respectively, representing the top level among reported heterogeneous Pd catalysts. By combining a study of first-principles density functional theory with experimental results, the superiority of Pd²⁺ over Pd⁰ was confirmed. Furthermore, the presence of V modified the electronic state of Pd²⁺, thus promoting the reaction. This study reports the effect of metal valence and electronic state on the catalytic performance for the first time and provides a new prospect for the design of an efficient heterogeneous catalyst for the hydrogenation of CO₂ to formic acid.