Effects of CO and NO atmospheres on the morphology of Ag, Ni, and Ir nanoparticles

Abstract

Metal nanoparticles are widely used in multiphase catalytic reactions due to their excellent physicochemical properties, which are mainly determined by their size and shape. Therefore, predicting and controlling the shape and structure of metal nanoparticles under reaction conditions has been a popular topic of interest among researchers. In this study, we conducted a systematical investigation to the equilibrium structure of Ag, Ni, and Ir nanoparticles within a mixed gas environment of CO and NO, employing a multiscale structural reconstruction model. This model demonstrates the ability to accurately predict the equilibrium configuration of metal nanoparticles under reactive conditions. Our investigation reveals a notable presence of negative surface energy in the phase diagrams representing Ag, Ir, and Ni nanoparticle configurations. This distinctive feature signifies that the nanoparticles undergo a process of splitting. While undergoing temperature and total pressure variations, the transformation in the structure of Ni nanoparticles is comparatively less evident in contrast to that of Ag and Ir nanoparticles. This discrepancy primarily stems from the pronounced energy barrier posed by the substantial rejection of CO and NO molecules at the surface of Ni nanoparticles. Notably, the structural modifications within Ag nanoparticles manifest solely within the confines of low-temperature ranges. Furthermore, our observations underscore the significant impact exerted by the ratios of CO and NO partial pressures on both the structure and the count of active sites within the metal nanoparticles.