Vanadium-containing mesoporous molecular sieves synthesized by both template-ion exchange (TIE) and direct hydrothermal (DHT) methods have been studied for partial oxidation of lower alkanes. UV-vis and in situ laser Raman spectroscopic studies suggest that the former synthetic method can provide tetrahedrally coordinated vanadium species mainly dispersed on the wall surface of MCM-41, while the latter method leads to vanadium sites mainly incorporated into the framework of MCM-41.H2-TPR measurements show that the vanadium species in the TIE samples can be reduced at lower temperatures than those in the DHT samples. NH3-TPD investigations suggest that weak acid sites mainly exist over MCM-41 along with a small amount of medium ones. The introduction of vanadium by the TIE method increased the amount of weak acid sites, while both weak and medium acid sites of MCM-41 are decreased with introducing vanadium up to a certain content by the DHT method. In the oxidations of ethane and propane, the alkane conversions increase remarkably with increasing vanadium content, and moderate selectivities to ethylene and propylene are obtained over the TIE catalysts. The same catalysts, however, are not elective for the oxidative dehydrogenation of isobutane. On the other hand, propylene and isobutene are obtained with high selectivity over the DHT catalysts with vanadium content exceeding 1wt% in the oxidations of propane and isobutane, respectively. Acrolein and methacrolein can also be formed respectively with considerable selectivity over the DHT catalysts with lower vanadium content. It is likely that the medium acid sites that remained in these samples play roles in the formation of oxygenates through the adsorption of alkenes or allylic intermediates.

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.

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.

A dramatic shift of allylic oxidation to epoxidation has been observed during the oxidation of propylene by N2O when the FeOx/SBA-15 catalyst is modified with alkali metal salts, and the roles of alkali metal salts are to suppress the reactivity of lattice oxygen and to induce an iron coordination structure effective for epoxidation with N2O.