In Situ Neutron Scattering Studies on the Oxidation and Reduction of CeO₂ and Pt–CeO₂ Nanorods

Abstract

The oxygen vacancy structure of ceria plays a key role in its performance as a favored material for catalysis applications. Here, we develop an understanding of the effects of Pt loading on the structural evolution of ceria nanorods under redox gas environments that mimic real automotive catalytic converters. In situ neutron scattering studies under redox flow reveal that both CeO2 and Pt–CeO2 nanorods share a bulk fluorite structure with the presence of surface Frenkel-type oxygen defects. However, Pt–CeO2 nanorods are more easily reducible than CeO2 rods as evidenced by an increased concentration of Ce3+, determined by NAP-XPS. Importantly, this work finds no evidence of oxygen vacancy ordered surface reconstruction which has been reported in earlier ex situ investigations. Thus, this work highlights the discrepancy between ex situ and in situ structural observations and emphasizes the need for robust in situ investigations of catalysts to develop industrially relevant materials.

Tuning the Metal–Support Interaction by Modulating CeO2 Oxygen Vacancies to Enhance the Toluene Oxidation Activity of Pt/CeO2 Catalysts

“…By comparison of JCPDS 34–0394 cards, both catalysts have strong diffraction peaks at 2θ angles equal to 28, 33, 47, and 56°. which were corresponding to the crystal faces of CeO 2 cubic fluorite structure (111), (200), (220), and (311), respectively . No diffraction peaks of other phases were observed, indicating that supports still maintain the cubic fluorite structure with treatment.…”

Tailored (La0.2Pr0.2Nd0.2Tb0.2Dy0.2)2Ce2O7 as a Highly Active and Stable Nanocatalyst for the Oxygen Evolution Reaction

“…Significantly, there is an increased concentration and longer correlation length scale of Nd/RE 1.5 Ce 1.5 O 5+ x in Nd 2 Ce 2 O 7 and RE 2 Ce 2 O 7 relative to the Ce 3 O 5+ x phase in CeO 2 . The correlation length scale of oxygen vacancies has been shown to strongly influence the redox properties and resulting catalytic performance of ceria‐based mixed oxides [ 54 ] and OER catalysts in general. [ 18 ]…”

“…To probe the nature of oxygen vacancies in both the average and local structure of the fluorite series, neutron total scattering analysis (Bragg diffraction, pair distribution function) was employed. Neutron diffraction and PDF have previously shown great sensitivity to the nature and length scale of oxygen vacancy correlations in catalysts [18,53,54] , being more sensitive probes of oxygen atoms relative to x-ray techniques. Rietveld refinements were performed on the neutron diffraction data for the fluorite samples calcined at 600°C as shown in Figure S4 (Supporting Information) with the corresponding refined parameters shown in Table S5 (Supporting Information).…”

“…To explore any deviation in the local oxygen vacancy structure of the fluorite series, the average structure models from neutron diffraction were applied to refinements of the neutron pair distribution functions (PDF) from 1. The correlation length scale of oxygen vacancies has been shown to strongly influence the redox properties and resulting catalytic performance of ceria-based mixed oxides [54] and OER catalysts in general. [18] XPS was used to further examine the variation in oxygen defect chemistry of these samples and determine the valence states of the elemental constituents present on the surface of the fluorite catalysts.…”