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

The reverse water-gas shift (RWGS, CO 2 + H 2 → CO + H 2 O, Δ H 298 = +0.44 eV) reaction mediated by the diatomic anion Rh 2 - was successfully constructed. The generation of a gas-phase H 2 O molecule and ion product [Rh 2 (CO) ads ] - 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 2 (CO) ads ] - . This experimentally identified Rh 2 - anion represents the first gas-phase species that can drive the RWGS reaction because it is challenging to design effective routes to yield H 2 O from CO 2 and H 2 . 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 2 or D 2 ) were fed into the reactor did not have a pronounced impact on the reactivity and the final product distribution (D 2 O and Rh 2 CO - ). The atomically precise insights into the key steps to guide the reaction toward the RWGS direction were provided.