Size-dependent catalytic reactivity of NO reduction by CO mediated by Rh_nV₂O₃⁻ clusters (n = 2–5)

A fundamental understanding of the precise structural characteristics of interfacial active sites present in heterogeneous catalysts is pivotal to construct a vigorous metal–support boundary. Herein, a series of RhnV2O3–5– (n = 2–5) clusters was theoretically designed, and we demonstrated that RhnV2O3–5– can catalytically reduce NO into N2 selectively by CO. We identified that in the structure of RhnV2O3−, Rhn moieties were dispersed on a V2O3 “support” anchored by two V atoms. The distance between the top Rh atom that was responsible for reactant capture, and the V atom in RhnV2O3− increased with an increase in the cluster size, resulting in less accessibility of V atoms in larger clusters during the reactions. A size-dependent behavior of NO reduction by RhnV2O3− was observed, where V atoms were always involved in the triatomic site of RhV2 or Rh2V in Rh2–4V2O3− to drive N–O rupture and N–N coupling, while NO reduction on Rh5V2O3− can be achieved by the cooperation of three Rh atoms. One Rh atom in Rh2–4V2O4,5− products also functioned as an anchoring site for CO and then delivered CO for oxidation by the nearby coordinated oxygen atom. This finding emphasizes that the recently identified triatomic active site Ceδ+–Rhδ−–Ceδ+ in RhCe2O3− for selective reduction of NO into N2 still prevails, but it behaves in a different manner in larger RhnV2O3− (n ≥ 5) clusters.