Co-containing molecular sieves, mainly Co–faujasite zeolite and Co-MCM-41, have been studied for the epoxidation of styrene with molecular oxygen. Characterizations with XRD, TEM, laser-Raman, XPS, and H2-TPR suggest that the cobalt introduced into MCM-41 by a template-ion exchange method resembles that exchanged in the faujasite zeolite and exists in the single-site Co(II) state, whereas the sample prepared by the impregnation method contains a large proportion of Co3O4. The Co(II) sites located in the molecular sieves catalyze the epoxidation of styrene by oxygen with higher activity than Co3O4 (ca. 2.6 times based on the same cobalt amount). On the other hand, in homogeneous reactions, Co(NO3)2 and Co(Ac)2 are almost inactive for the conversion of styrene with oxygen, whereas CoCl2 and Co(acac)3 show some activity, but the selectivity for epoxide is remarkably lower as compared with the Co(II)-containing molecular sieves. Among various oxidants examined, oxygen is found to be the best one for the epoxidation of styrene over the Co(II)-containing molecular sieve catalysts. The solvent plays an important role in epoxidation, and superior catalytic performances have been obtained with an acylamide such as N,N-dimethylformamide (DMF) as the solvent. The oxygen species with a radical nature generated by the activation of molecular oxygen over the solvent-coordinated Co(II) site has been proposed for the epoxidation reactions.

Magnetite iron oxide (Fe3O4) has been found to be an efficient heterogeneous catalyst for the epoxidation of alkenes by molecular oxygen in the absence of a sacrificial reductant among various transition metal oxides. The reaction probably proceeds via a radical mechanism.

Cobalt oxide (CoOx) particles within faujasite zeolites have been synthesized by a procedure comprising (i) ion-exchange of cobalt ions into the zeolite, (ii) precipitation of cobalt ions with sodium hydroxide within the supercages of the zeolite, and (iii) calcination. The materials are characterized by XRD, nitrogen sorption, XPS, TEM-EDS, H2-TPR, and O2-titration. The concentration of sodium hydroxide for precipitation and the temperature for calcination are found to be critical in controlling the locations of the CoOx particles. With appropriate conditions, the CoOx particles formed are located and encapsulated in the supercages of faujasite zeolites. The sizes of the CoOx particles are in the range of 0.7-3nm with a maximum distribution of 1.3-1.5nm. These particles exist mainly in the state of CoO. On the other hand, higher calcination temperature or higher concentration of sodium hydroxide may lead to the formation of larger Co3O4 particles located outside the supercages of the faujasite zeolites. The CoOx particles encapsulated in the supercages exhibit a broad reduction peak and can be partly reduced to metallic cobalt at temperatures as low as 573K, while the cobalt cations exchanged into the zeolites can only be reduced at temperatures higher than 773K. The metallic cobalt formed by the reduction of cobalt oxide within the supercage exhibits superior catalytic activity in Fischer-Tropsch synthesis.

SBA-15-supported iron phosphate (FePO4) has been characterized with XRD, TEM, Raman spectroscopy and H2-TPR, and studied for the partial oxidation of CH4 with O2. The characterizations suggest that the FePO4 species with loading amount lower than 40 wt.% are encapsulated within the mesoporous channels of SBA-15, and these species possibly exist as small FePO4 clusters with the local coordination environment of iron being similar to that in the crystalline FePO4. However, these encapsulated FePO4 clusters could be reduced at remarkably lower temperatures than the crystalline FePO4. The SBA-15-supported FePO4 catalysts exhibit higher CH4 conversion and HCHO selectivity than the unsupported and the MCM-41-supported ones in the partial oxidation of CH4 with O2. The catalyst with a loading amount of 5 wt.% shows the highest HCHO selectivity at a given CH4 conversion and the highest HCHO formation rate based on the amount of FePO4 in the catalyst. It is likely that the improved catalytic performances of the SBA-15-supported samples are related to the enhanced redox properties of FePO4 species, the large porous diameter and the high inertness of SBA-15.

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.