Reverse water-gas shift reaction catalyzed by diatomic rhodium anions.

The reverse water-gas shift (RWGS, CO + H → CO + HO, Δ = +0.44 eV) reaction mediated by the diatomic anion Rh was successfully constructed. The generation of a gas-phase HO molecule and ion product [Rh(CO)] was identified unambiguously at room temperature and the only elementary step that requires extra energy to complete the catalysis is the desorption of CO from [Rh(CO)]. This experimentally identified Rh anion represents the first gas-phase species that can drive the RWGS reaction because it is challenging to design effective routes to yield HO from CO and H. The reactions were performed by using our newly developed double ion trap reactors and characterized by mass spectrometry, photoelectron spectroscopy, and high-level quantum-chemical calculations. We found that the order that the reactants (CO or D) were fed into the reactor did not have a pronounced impact on the reactivity and the final product distribution (DO and RhCO). The atomically precise insights into the key steps to guide the reaction toward the RWGS direction were provided.