Siliceous FSM-16 possesses acid sites to catalyze but-1-ene isomerization to produce but-2-ene (cis/trans ) 1.4-1.7) at 323 K and 2,6,6-trimethylbicyclo[3.1.1]hept-2-ene (R-pinene) isomerization at 303 K. Catalytic activity was dependent upon heat treatment and reached a maximum at 673 K. The maximum acid strength was invariably H 0 ) -3.0 independent of the pretreatment temperatures. The acidity was much reduced by calcination at higher temperatures, but restored by water treatment at 353 K as long as the FSM-16 retained its structure.

Silica-supported molybdenum oxide (MoO3/SiO2) and alkali-ion-modified MoO3/SiO2 samples were characterized by Mo K-edge XAFS and Raman spectroscopies. The structure of the molybdenum species in MoO3/SiO2 was confirmed to be monomeric and tetrahedral, (OMoO)O2. In alkali-ion-modified MoO3/SiO2, the structure of the molybdenum species varied with the kinds and/or the amounts of added alkali ions. In Na+-modified MoO3/SiO2 with sodium ions of the molar ratio Na/Mo < 1.0, the molybdenum species were mainly Na2Mo2O7 besides (OMoO)O2 which was present in MoO3/SiO2, and the addition of sodium ions of molar ratio Na/Mo > 1.0 caused the formation of Na2MoO4 at the expense of Na2Mo2O7. In the case of K+- and Rb+-modified MoO3/SiO2, the addition of alkali ions equimolar with the molybdenum atoms in the samples brought about the formation of Mo2O7 species, and by the addition of alkali ions of molar ratio (alkali ion/Mo) > 1.0, MoO4 species was formed on the silica support. In the molybdenum species in K-MS and Rb-MS with alkali ions of molar ratio (alkali ion/Mo) < 1.0, the proportion of an octahedral MoO6 unit to all the molybdenum species in the samples was higher than that in K-MS and Rb-MS with alkali ions of the molar ratio > 1.0.

NiO−MgO samples (Ni x Mg1-x O:x = moles of Ni/(moles of Ni + moles of Mg)) were prepared by impregnation of MgO powder with an aqueous solution of Ni(NO3)2, followed by calcination at 773 K. The dispersion of Ni ions in these samples has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). XPS of the depth profile of the samples shows that the atomic concentration of Ni and Mg against the depth is almost constant and close to those of bulk concentrations. The analyses by EXAFS and XANES reveal the absence of the preferential segregation of nickel oxide phase or magnesium oxide phase in all samples, suggesting the substitution of Ni ions for Mg ions. A detailed analysis by the curve-fitting method indicates that Ni ions dissolving into MgO are dispersed at random, regardless of the compositions of the samples. These results suggest that these samples form solid solutions over the entire composition range, even by calcination at 773 K.

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.

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.