The coordination structures of vanadium and iron introduced into MCM-41, a typical mesoporous silica, by both direct hydrothermal synthesis (DHT) and templateion exchange (TIE) methods have been studied by X-ray absorption spectroscopy (XANES and EXAFS). Vanadium is tetrahedrally coordinated with oxygen in V-MCM-41 prepared by both methods but the location of vanadium is probably different; vanadium is mainly incorporated inside the framework of MCM-41 by the DHT method as the content is lower than approximately 1wt%, while the vanadyl tetrahedra are probably dispersed on the wall surface of MCM-41 over the samples by the TIE method. In the case of Fe-MCM-41, the DHT method results in iron atoms mainly in tetrahedral coordination and isolated from each other in the framework of MCM-41. However, aggregated iron oxides with iron in octahedral coordination are mainly observed in the TIE samples. The V-MCM-41 by the TIE method shows better catalytic performances than that by the DHT method in the partial oxidation of methane to formaldehyde with oxygen. However, the Fe-MCM-41 by the DHT method exhibits remarkably higher methane conversion and formaldehyde selectivity than that by the TIE method.

Cr-MCM-41 prepared by direct hydrothermal synthesis (DHT) and template-ion exchange (TIE) has been characterized by X-ray diffraction (XRD), N2 adsorption (77K), diffuse reflectance UV-vis, X-ray absorption (XANES and EXAFS), and UV-Raman spectroscopic measurements. It is suggested that monochromate species mainly exist on the Cr-MCM-41 by the DHT method while several types of chromate species including both monochromates and polychromates coexist on that by the TIE method. The two kinds of samples exhibit similar catalytic property in the dehydrogenation of propane with carbon dioxide. The selectivity to propylene is higher than 90% and the presence of carbon dioxide enhances propane conversion. The chromate species on both types of samples are reduced to aggregated Cr(Ⅲ) with octahedral coordination during the dehydrogenation reactions. On the other hand, the selectivity to formaldehyde in the partial oxidation of methane with oxygen is remarkably higher over the sample by the DHT method than that by the TIE method. The structure of the chromate species is kept during the oxidation of methane, and the high dispersion of monochromate species probably accounts for the higher selectivity over the sample by the DHT method.

Co2+-Exchanged faujasite zeolites can efficiently catalyze the epoxidation of styrene with molecular oxygen, and the Co2+ ions located in supercages are suggested to account for the activation of O2 for the epoxidation of styrene.