Probing the Structure-Property Relationships of Metal Oxide Nanocatalysts

This work is aimed at uncovering the role of structural defects and disorder on the properties of metal oxide nanoparticles for emissions control and electrochemical catalytic applications. This understanding is achieved through: (i) synthesis of traditional and novel catalysts; (ii) catalytic performance testing; and (iii) in-situ structural characterization via neutron scattering.

Metal oxide nanomaterials impregnated with noble metals serve as benchmark catalysts for a wide range of catalytic reactions. We investigate the influence of noble metals on the defect structure of the underlying support with a focus on emissions control catalysis. Neutron total scattering was employed to investigate the structural evolution of CeO₂ and Pt-CeO₂ nanorods in-situ under oxidation and reduction. The need for in-situ characterization environments motivated the design of a hazardous gas handling system (HGHS), high temperature furnace and quartz sample cell designed to enable in-situ gas flow at the Nanoscale-Ordered Materials Diffractometer (NOMAD) instrument at the Spallation Neutron Source. This new in-situ gas flow set up was commissioned by studying the structural evolution of CeZrO4 and Pd-CeZrO4 under oxidation, methane oxidation and methane reduction. In this system, Pd is found to have a profound impact on the evolution of the underlying support. In both studies, neutron total scattering proves to be a valuable tool in uncovering the nature and evolution of oxygen vacancies and local cation ordering within catalyst supports, which may be challenging to resolve using other characterization techniques.

Despite their high activity, the scarcity, high cost and instability of noble metal based catalysts presents major drawbacks. We leverage compositional complexity to design RE_0.5Ce_0.5O_2-x catalysts, where RE = a single or multiple rare earth cation(s), as noble metal-free electrocatalysts for the oxygen evolution reaction (OER). Incorporating a single RE cation into the fluorite lattice boosts OER activity, further enhanced by the compositionally complex oxide composition that increases oxygen vacancies, reducing the energy required for OH* adsorption. Thus, tuning compositional complexity may offer promising improvements in OER catalytic activity.

Our findings yield new perspectives on designing industrially viable metal oxide nanocatalysts and advance the applicability of neutron total scattering for studying materials in-situ under gas flow.