Ab initio insights into the structural, energetic, electronic, and stability properties of mixed CenZr15−nO30 nanoclusters

Abstract

Mixed CeO₂–ZrO₂ nanoclusters have the potential to play a crucial role in nanocatalysis, however, the atomistic understanding of those nanoclusters is far from satisfactory. In this work, we report a density functional theory investigation combined with Spearman rank correlation analysis of the energetic, structural and electronic properties of mixed Ce_nZr_15−nO₃₀ nanoclusters as a function of the composition (n = 0, 1,…,14, 15). For instance, we found a negative excess energy for all putative global minimum Ce_nZr_15−nO₃₀ configurations with a minimum at about n = 6 (i.e., nearly 40% Ce), in which both the oxygen anion surroundings and cation radii play a crucial role in the stability and distribution of the chemical species. We found a strong energetic preference of Zr⁴⁺ cations to occupy larger coordination number sites, i.e., the nanocluster core region, while the Ce⁴⁺ cations are located near vacuum exposed O-rich regions. As expected, we obtained an almost linear decrease of the average bond lengths by replacing Ce⁴⁺ by Zr⁴⁺ cations in the (ZrO₂)₁₅ nanoclusters towards the formation of mixed Ce_nZr_15−nO₃₀ nanoclusters, which resulted in a shift towards higher vibrational frequencies. Besides, we also observed that the relative stability of the mixed oxides is directly correlated with the increase (decrease) of the Zr d-state (Ce f-state) contribution to the highest occupied molecular orbital with the increase of the Zr content, hence driving the gap energy towards higher values.