Perovskites as substitutes of noble metals for heterogeneous catalysis: dream or reality.

Oxygen vacancy (O-vacancy) is essential in catalytic oxidation but little is known about its insight. Herein, a series of MnOx-CeO2 catalysts with various Mn/(Mn + Ce) molar ratios were synthesized with citric acid complex method for O-vacancy study in soot catalytic combustion. The samples were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, O2-temperature programmed desorption (O2-TPD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy. It has been shown that MnOx(0.4)-CeO2 catalyst presented more O-vacancies, thus exhibiting the highest catalytic activities and redox properties. With the utilization of in situ Raman, two types of O-vacancies, including Frenkel-type oxygen vacancy (F OV) and intrinsic oxygen vacancy (I OV), were clarified. Furthermore, the transform relation between F OV and I OV was found. Those two types of O-vacancies favored to the migration and transformation of active species, enhancing further the oxidation-reduction cycle and the catalytic activity for soot oxidation. In addition, Mn4+/Mn3+(Mn2+), Olatt, Osur and Ce4+/Ce3+ were believed to play important roles in soot oxidation. Finally, evolution of O-vacancies was proposed, which is of significance for soot catalytic oxidation.

Evolution of oxygen vacancies in MnOx-CeO2 mixed oxides for soot oxidation

Traditional nanostructured design of cerium oxide catalysts typically focuses on their shape, size, and elemental composition We report a different approach to enhance the catalytic activity of cerium oxide nanostructures through engineering high density of oxygen vacancy defects in these catalysts without dopants The defect engineering was accomplished by a low pressure thermal activation process that exploits the nanosize effect of decreased oxygen storage capacity in nanostructured cerium oxides

http://ncesr.unl.edu/wordpress/wp-content/uploads/2011/01/11-07-11-511-Zeng-Defect-Engineering-in-Cubic-Cerium-article.pdf

Defect Engineering in Cubic Cerium Oxide Nanostructures for Catalytic Oxidation

Here we report the photocatalytic activity of CeO2 nanoparticles. This is carried out with methyl orange as the reference pollutant. Annealing of ceria under vacuum generates oxygen deficient CeO2 nanoparticles with defects such as oxygen vacancies and formation of Ce3+. This is evident from the characterization results of X-ray diffraction, Raman spectroscopy, N2 adsorption–desorption and X-ray photoelectron spectroscopy. The band gap is red shifted due to the creation of intermediate energy states of Ce3+ and oxygen vacancies in the band gap. The reduced photoluminescence (PL) intensity of defective ceria indicates that the electron–hole separation is substantially enhanced by the surface trap centers. Air annealed ceria not only has relatively low surface area but also has fewer surface defects. Thus, it is expected to display less photocatalytic activity. Vacuum annealed CeO2 indeed displays better photocatalytic activity in the degradation of methyl orange under UV and visible light as compared to the air annealed samples.

Oxygen defects and formation of Ce3+affecting the photocatalytic performance of CeO2nanoparticles

Ceria-based catalysts for soot oxidation: a review

Catalytic oxidation of soot particulates over MnOx-CeO2 oxides prepared by complexation-combustion method

Catalytic oxidation of diesel soot particulates over Ag/LaCoO3 perovskite oxides in air and NOx

Controllable preparation of CeO2 nanostructure materials and their catalytic activity

This article reports a novel preparation of three-dimensional (3D) CeO2 originating from crystalline cerium formate by a surfactant-free route using H2O, ethanol and ethylene glycol as solvents. The sea urchin shaped 3D CeO2 gave rise to micro/nanocomposite structures with high BET surface area up to 234 m2 g−1. The 3D structure improved the reducibility of surface CeO2 due to the increased oxygen vacancy. Both 3D CeO2 and 5 wt% CuO loaded on 3D CeO2 exhibit high catalytic activities for CO conversion.

Wenjuan Shan

Papers

Catalytic oxidation of soot particulates over MnOx-CeO2 oxides prepared by complexation-combustion method

Catalytic oxidation of diesel soot particulates over Ag/LaCoO3 perovskite oxides in air and NOx

Controllable preparation of CeO2 nanostructure materials and their catalytic activity

The Synthesis of Three-Dimensional CeO2 and Their Catalytic Activities for CO Oxidation

Catalytic Activity and Stability of K/CeO2 Catalysts for Diesel Soot Oxidation