X-ray photoelectron and Raman spectroscopy of nanostructured ceria in soot oxidation under operando conditions. (30th June 2021)

• Record Type: Journal Article
• Authors: Garcia, Xènia; Soler, Lluís; Casanovas, Albert; Escudero, Carlos; Llorca, Jordi
• Is Part Of: Carbon. Volume 178(2021)
• Page Start: 164
• Page End: 180
• Publication Date: 2021-06-30
• Subjects: Ceria -- Nanoshapes -- Soot oxidation -- NAP-XPS -- AP-XPS -- Raman spectroscopy -- Operando characterization; Carbon -- Periodicals; Carbone -- Périodiques; Koolstof; Toepassingen; Electronic journals; 546.681
• DOI: 10.1016/j.carbon.2021.03.009
• Languages: English
• ISSNs: 0008-6223

Abstract

Abstract: Ceria nanoshapes exhibiting different amounts of {100}, {110} and {111} facets (cubes, rods, octahedra and polyhedra) were prepared, characterized, tested in the carbon soot oxidation reaction, and studied by operando near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando Raman spectroscopy up to 550 °C. The specific soot oxidation reaction rate (mgC ·m −2 ·min −1 ) clearly indicated that the {110} and {100} crystallographic planes of ceria were more active than the {111} ones for the oxidation of carbon soot. As deduced from the Ce 3d and O 1s signals recorded using different photon energies, all ceria nanoshapes experienced progressive reduction upon increasing the temperature under Ar, which was accompanied by the formation of oxygen vacancies. Raman studies revealed that, at this stage, isolated graphene layers in carbon soot reacted with ceria lattice oxygen atoms following a Mars-Van Krevelen mechanism. After exposure to O2 at 550 °C, a broad signal in the O 1s region at 531.2–532.5 eV was ascribed to surface active oxygen species, such as peroxide (O2 2− ) and superoxide (O2 − ) species, generated from the interaction of molecular O2 with oxygen vacancies, which proved to be highly reactive to oxidize the graphitic structures of carbon soot. Graphical abstract: Image 1 Highlights: Ceria nanoshapes are studied by operando AP-XPS and Raman for soot oxidation. Reconstruction of {100} and {110} into {111} facets induced by thermal treatment. Soot boosts ceria reduction on {100} and {110} and oxygen vacancies upon heating. Isolated graphene layers react with ceria lattice oxygen atoms by a MVK mechanism. Surface oxygen species generated from O2 and oxygen vacancies are very reactive.