Equilibrium morphology evolution of FCC cobalt nanoparticle under CO and hydrogen environments

Abstract

Metal nanoparticles could change their shape and exposed certain facet under specific reaction conditions, resulting in greatly influence the performance of catalysts in heterogeneous catalysis. Combining spin-polarized density functional theory and ab initio atomistic thermodynamics, the equilibrium morphology evolution of FCC cobalt nanoparticle had been investigated under CO and hydrogen environments. The phase diagram clearly revealed the stable coverage could be affected by temperature and CO and hydrogen partial pressure. According to the surface energies of four surfaces, Wulff construction was introduced to characterize the morphologies of the Co catalyst at diverse temperatures and pressures. At the typical temperature (675 K) of hydrogen reduction, the estimated surface proportion ratio of the Co(3 1 1) exposed the B5 site could exist a marked increase, which was also consistent with the available Co catalyst reduced under experimental conditions. Our results would give direct insights into the understanding and quantitative description of structure evolution as well as active facets of the Co nanoparticles under the realistic FTS reaction condition.