Size-dependent catalytic reactivity of NO reduction by CO mediated by RhnV2O3− clusters (n = 2–5)†

Abstract

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 Rh_nV₂O_3–5^– (n = 2–5) clusters was theoretically designed, and we demonstrated that Rh_nV₂O_3–5^– can catalytically reduce NO into N₂ selectively by CO. We identified that in the structure of Rh_nV₂O₃⁻, Rh_n 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 Rh_nV₂O₃⁻ 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 Rh_nV₂O₃⁻ was observed, where V atoms were always involved in the triatomic site of RhV₂ or Rh₂V in Rh_2–4V₂O₃⁻ 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 Rh_2–4V₂O_4,5⁻ 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 Ce^δ+–Rh^δ−–Ce^δ+ in RhCe₂O₃⁻ for selective reduction of NO into N₂ still prevails, but it behaves in a different manner in larger Rh_nV₂O₃⁻ (n ≥ 5) clusters.