New opportunities for tailored nanoparticle catalysts through exsolution from inherently disordered defect fluorite-type oxides†

Abstract

Nanoparticle exsolution from oxide supports has emerged as a promising strategy for designing highly active and stable catalysts, with perovskite oxides being the most explored support structures to date. In this study, we successfully demonstrate exsolution from the novel Y₂Zr_2−xRu_xO₇ (0 ≤ x ≤ 0.2) defect fluorite system, probe the factors governing the extent of exsolution in this system, and evaluate the performance of these exsolved materials as catalysts for CO₂ conversion. X-ray photoelectron spectroscopy measurements performed both under vacuum and near-ambient pressure conditions give unique insight into the evolution of the chemical state of ruthenium substituents during exsolution, providing evidence for the existence of intermediate reduction steps before eventual reduction to metallic ruthenium. The distribution of chemical states and extent of reduction to metallic ruthenium exhibit a strong dependence on both the duration and temperature of the reductive treatment applied, with both potentially limiting the extent of reduction at a given partial pressure of oxygen. STEM-EDX characterisation reveals the formation of well-dispersed metallic ruthenium nanoparticles over the unique, nanoporous morphology of the host structure. Preliminary testing for the reverse-water-gas-shift reaction demonstrates promising performance, achieving CO₂ conversion close to thermodynamic equilibrium and 100% CO selectivity above 650 °C. These findings provide new insights into exsolution from the defect fluorite system and expand the range of host materials available within the exsolution design space for advanced catalysts in energy-related applications.