Kinetic Study on Solid-Phase Reduction of Silica-Supported Nickel Oxide Species

• Published in: Bulletin of the Chemical Society of Japan Vol. 88; no. 12; pp. 1629 - 1635
• Main Authors: Yamashita, Shohei, Yamamoto, Yusaku, Katayama, Misaki, Inada, Yasuhiro
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 15.12.2015; Chemical Society of Japan
• Subjects: Catalysts; Fine structure; Metal oxides; Nickel; Reduction; Roasting; Silicon dioxide; Transmission electron microscopy
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.20150243

The X-ray absorption fine structure (XAFS) spectroscopy was used to analyze the chemical state conversion of the Ni species in SiO2-supported Ni catalysts which were prepared by the impregnation method with various Ni loadings. The in situ XAFS measurements revealed that the calcined NiO species was quantitatively reduced by H2 to Ni(0) at around 580 K, and the formed Ni(0) species was reversibly and gradually oxidized by O2 up to 873 K. The transmission electron microscopy observation clarified that the Ni(0) particle size was dependent on the Ni loading. The dynamic observations using the time-resolved dispersive XAFS technique showed that the reduction process could be described by the first-order kinetics on the Ni species, which was different from the reduction kinetics of supported PdO species, which is a divalent metal oxide for the same family element. The different reduction kinetics is ascribed by the different atomic arrangement in the crystal structure between NiO and PdO.