NO oxidation catalyzed by Ir4-based nanoclusters: the role of alloying on the catalytic activity

Abstract

Owing to the catalytic performance of Ir4 cluster, proven in earlier experimental studies, we have investigated NO oxidation on the Ir4 by density functional theory calculations. The Langmuir–Hinshelwood (LH) mechanism is explored to gain insights into the fundamental mechanism for the reaction of NO and O2. The adsorption energies, reaction pathways, and reaction barriers are calculated systematically for square planar and tetrahedral geometries of Ir4 clusters. It is observed that the reaction profiles for NO oxidation on tetrahedral and square planar geometries of Ir4 are quasi-degenerate. From the point of view of the catalyst design, we have also studied the effect of alloying on the reactivity and catalytic behavior of the Ir4 cluster by introducing Ag, Cu, Co, and Rh atoms. We show that the calculated barriers for the reactions mediated by bimetallic clusters Ir3Ag, Ir3Cu, Ir3Co, and Ir3Rh are comparable with that catalyzed by monometallic Ir4 cluster, implying that the catalytic activity of Ir centers in the bimetallic clusters seems not to be dependent on its surroundings. Nonetheless, the formation of the second NO2 over the Ir3M clusters requires lower activation energy which may facilitate the catalyst recovery.