Reverse water-gas shift catalyzed by Rh n VO 3,4 - ( n = 3-7) cluster anions under variable temperatures.

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) (CO 2 + H 2 → CO + H 2 O) catalyzed by a series of compositionally and structurally well-defined Rh n VO 3,4 - ( n = 3-7) clusters were identified under variable temperatures (298-773 K). It is discovered that the Rh 5-7 VO 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 n VO 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 5-7 VO 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.