Reverse water–gas shift catalyzed by RhnVO3,4− (n = 3–7) cluster anions under variable temperatures

Abstract

A fundamental understanding of the exact structural characteristics and reaction mechanisms of interface active sites is vital to engineering an energetic metal–support boundary in heterogeneous catalysis. Herein, benefiting from a newly developed high-temperature ion trap reactor, the reverse water–gas shift (RWGS) (CO₂ + H₂ → CO + H₂O) catalyzed by a series of compositionally and structurally well-defined Rh_nVO_3,4⁻ (n = 3–7) clusters were identified under variable temperatures (298–773 K). It is discovered that the Rh_5–7VO_3,4⁻ clusters can function more effectively to drive RWGS at relatively low temperatures. The experimentally observed size-dependent catalytic behavior was rationalized by quantum-chemical calculations; the framework of Rh_nVO_3,4⁻ is constructed by depositing the Rh_n clusters on the VO_3,4 “support”, and a sandwiched base–acid–base [Rh_out⁻–Rh_in⁺–VO_3,4⁻; Rh_out and Rh_in represent the outer and inner Rh atoms, respectively] feature in Rh_5–7VO_3,4⁻ governs the adsorption and activation of reactants as well as the facile desorption of the products. In contrast, isolated Rh_5–7⁻ clusters without the electronic modification of the VO_3,4 “support” can only catalyze RWGS under relatively high-temperature conditions.