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Mo L3-edge XANES and diffuse reflectance UV−vis spectra have been recorded for structural studies of Mo−Mg binary oxides which catalyze metathesis reactions of olefins after pretreatment with H2 at 773 K. The XANES of reference compounds revealed that the local symmetry around the Mo ion as well as the valence state affects the spectral features. From the XANES of Mo−Mg binary oxides in oxidized/reduced states, it is concluded that MoO4 tetrahedra are the main component in the near-surface region for samples of x (Mo/(Mo + Mg)) ≤ 0.7 in the oxidized state. For samples in the reduced state, the tetrahedral species remain, but reduced Mo ions including MoO2 species are also formed, while the MoO2 phase is formed in the bulk phase at x = 0.5−0.8. In the latter samples, Mo ions are easily reduced by treatment with H2. The active species for metathesis reactions relates to formation of the MoO2 phase not only in the bulk but also in the near-surface region.

In the present study, the preparation of dense hydroxyapatite (HAp) materials at relative low temperatures using a spark plasma sintering was carried out. The bioactivity of HAp samples prepared by a spark plasma sintering method was investigated by in vitro tests and compared with HAp obtained by a conventional hot-pressing method. No growth of bone-like HAp crystals on surface of HAp sintered by a conventional hot-pressing method at 1200 degrees C was observed after immersion in a simulated body fluid (SBF) for 2 days. However, many large bone-like HAp crystals were observed on the surface of HAp samples prepared by a spark plasma sintering at 1200 degrees C after 2 days in the SBF immersion test. Especially, the negatively charged surface of the HAp samples prepared by spark plasma sintering was covered with larger HAp crystals compared with the positively charged surface. The electric poling of HAp was measured using a thermally simulated current technique. This rapid growth of bone-like HAp crystals of the HAp samples made by spark plasma sintering was believed to be related with the OH(-) and/or Ca(2(+) ) ion deficiency at the grain boundaries of the HAp matrix grains as well as a small electric poling effect resulting during the spark plasma sintering process.

The local structure around Mo atoms in Mo-Mg binary oxides has been investigated by X-ray absorption spectroscopy at Mo and Mg K edges. XANES and EXAFS spectra show that the binary oxides have a tetrahedral MoO 4 unit in the samples with a Mo/(Mo + Mg) ratio of less than 0.5 and an octahedral MoO 6 unit in the samples with a higher ratio. By H 2 treatment at 773 K, a molybdena-rich binary oxide was easily reduced to form the MoO 2 phase, which was not detected by XRD but was by EXAFS. It is concluded that the reduced oxide contains low valent Mo ions in the MoO 2 phase and the ions work as an active center for propene metathesis.