The structural change of Ru/CeO2 and Ru/SiO2 catalysts during pretreatments was investigated by in situ Ru K edge quick-scanning X-ray absorption fine structure (XAFS) combined with temperature-programmed reduction with H2 and X-ray diffraction (XRD). After impregnation and drying, two pretreatment sequences were applied: (i) calcination in air at 573 K and reduction with H2 and (ii) heating in inert gas at 573 K and reduction with H2. In sequence (i) of Ru/CeO2, the extended XAFS (EXAFS) spectra showed the formation of crystalline RuO2 during calcination. On the other hand, in sequence (ii) of Ru/CeO2 and Ru/SiO2, the EXAFS results indicated that the Ru oxide was still noncrystalline after heating. The size of Ru metal particle during reduction was determined by Ru-Ru coordination number in EXAFS (CNRu-Ru) and reduction degree. The size was almost constant for Ru/CeO2 (CNRu-Ru: about 4) or Ru/SiO2 (CNRu-Ru: about 8) in sequence (ii), indicating the absence of aggregation. The size was increased for Ru/CeO2 in sequence (i); however, the XRD results suggested that each RuO2 crystallite was slowly reduced to one Ru particle. After all, aggregation during reduction was not significant for all Ru/CeO2 and Ru/SiO2 catalysts.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films