Due to their activity and cost effectiveness, atomically dispersed transition metals are highly desirable catalysts. In addition, their uniform active sites enable high selectivity. However, sintering into larger particles is thermodynamically favorable in the absence of strong metal–support interactions. Using density functional theory, we study the stability of atomically dispersed transition metals on different support materials and their activity toward CO oxidation. We find that the late transition metals Pd and Pt bind strongly to oxygen vacancies of MeO (Me = Fe, Mg, Mn, and Ni), and that their atomic dispersion is thermodynamically favorable at low metal loadings. The resulting single-atom catalysts enable CO oxidation with barriers as low as 40 kJ/mol. The intrinsic barriers were found to depend primarily on the nature of the transition metal. These findings are in good agreement with previous experimental work on Pd1/MgOX catalysts that enable CO oxidation at 260 K. However, the Pd1/MgOX catalyst is deactivated after the first oxidation step, as it leads to a metastable PdO/MgOX species, which can heal the O vacancy. Without the vacancy, nanoparticle formation is thermodynamically favorable. Due to their lower oxygen vacancy formation energies, reducible oxide supports are predicted to be more resistant to sintering. Thus, the anion vacancy formation energy of the support is an important parameter for the stability of anionic single-atom catalysts, while their activity depends primarily on the nature of the transition metal atom. These atomistic insights can be used to design even more stable single-atom catalysts for CO oxidation at low temperatures.

Identifying single-atom catalysts for CO oxidation from density functional theory

2019 Fall National Meeting

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