Particle size effect of redox reactions for Co species supported on silica

•The conversions of the chemical state of supported Co species during redox reaction are evaluated.•In operando XAFS technique were applied to measure redox properties of small Co particles.•A small particle size affects to the redox temperatures of cobalt catalysts.

Conversions of chemical states during redox reactions of two silica-supported Co catalysts, which were prepared by the impregnation method, were evaluated by using an in situ XAFS technique. The addition of citric acid into the precursor solution led to the formation on silica of more homogeneous and smaller Co particles, with an average diameter of 4 nm. The supported Co3O4 species were reduced to metallic Co via the divalent CoO species during a temperature-programmed reduction process. The reduced Co species were quantitatively oxidized with a temperature-programmed oxidation process. The higher observed reduction temperature of the smaller CoO particles and the lower observed oxidation temperature of the smaller metallic Co particles were induced by the higher dispersion of the Co oxide species, which apparently led to a stronger interaction with supporting silica. The redox temperature between CoO and Co3O4 was found to be independent of the particle size.

Graphical abstractChemical state conversions of SiO2-supported Co species and the particle size effect have been analyzed by means of in situ XAFS technique. The small CoO particles have endurance against the reduction and exist in a wide temperature range.Figure optionsDownload full-size imageDownload as PowerPoint slide