Resolving a Decade-Long Question of Oxygen Defects in Raman Spectra of Ceria-Based Catalysts at Atomic Level

Abstract

Oxygen defects play a critically important role in redox reactions on ceria-based catalysts. Raman spectroscopy is a key technique for the characterization of oxygen defects in ceria catalysts. However, the assignment of oxygen defects in Raman spectra has been in dispute for decades. In this work, combining density functional theory calculation with characterization of model composites, we resolved the long-standing question in Raman spectra of ceria-based catalysts at the atomic level. The Raman peak at 460 cm–1 is attributed to the wagging vibration of O atom between two Ce4+ ions, and its position varies with the length of Ce—O bond in ceria-based catalysts. The Raman band at about 560 cm–1 is derived from the stretching vibration of O atom between M3+ and Ce4+ ions near oxygen defects, whereas the Raman band at about 600 cm–1 is due to the stretching vibration of O atom between Mn+ and Ce4+ ions without oxygen defects. New indicators are proposed to establish the possible quantitative structure–activity relationship (QSAR) of ceria-based catalysts. We anticipate that the definite assignment of Raman peaks of oxygen defects in ceria-based catalysts provides a new insight into the design and development of ceria-based catalysts, and the conclusion and method herein can be employed to study the QSAR of other metal oxides.