Small phosphorus-modified molybdenum oxide clusters encapsulated inside the mesoporous channels of SBA-15 exhibit excellent catalytic performance for the partial oxidation of methane to formaldehyde with oxygen. A formaldehyde selectivity of 90% has been obtained at a single-pass methane conversion of 5.8%.

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.

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.

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.