CeO2−xNx Solid Solutions: Synthesis, Characterization, Electronic Structure and Catalytic Study for CO Oxidation

In this work, CeO2−xNx materials have been prepared by the solution combustion method. All the prepared materials were characterized by powder-XRD, TEM, ICP–AES, RAMAN and XPS techniques. XRD and TEM confirmed 6–18 nm particles of CeO2−xNx materials (UC10, UC7, UC4 and UC1). Among different materials, UC10 showed the highest number of oxygen vacancies (Raman). With increase in U/C (fuel/oxidizer) ratio, the particle size decreased, whereas the specific surface area and oxygen vacancies increased. The oxygen vacancies are created because of charge imbalance and lattice distortion in ceria. The presence of N in ceria causes smaller crystallites and large specific surface area. XPS indicates N–Ce–O environment in CeO2−xNx materials. It is observed that oxygen vacancies created by nitrogen doping play an important role in cerium oxynitrides for CO oxidation reaction. The catalytic order of CeO2−xNx materials is as follows: UC10 > UC7 > UC4 > UC1. This is due to the larger number of oxygen vacancies possessed by UC10 material as compared to others. UC10 also showed an excellent 24 h time-on-stream stability for CO oxidation. The apparent activation energy of UC10 is found to be 51.1 kJ mol−1. This shows that CeO2−xNx materials are highly active and stable for CO oxidation.