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.

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.

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%.

Iron-containing mesoporous molecular sieves (Fe-MCM-41) synthesized by both direct hydrothermal (DHT) and template-ion exchange (TIE) methods have been characterized and used as catalysts for the liquid-phase epoxidation of styrene with diluted H2O2. The characterizations with XRD, diffuse reflectance UV-vis, ESR, andEXAFSsuggest that iron cations are highly dispersed and tetrahedrally coordinated with oxygen in the DHT samples with iron content lower than ca. 0.9-1.1 wt% (Si/Fe=105-86). This coordination environment is similar to that in a ferrisilicate zeolite with MFI structure and contributes to the increase in relative strong acidic sites, as indicated by NH3-TPD studies. On the other hand, the TIE samples mainly contain small iron oxide clusters. The conversion of styrene over the DHT catalyst increases significantly with increasing iron content up to 1.1 wt%. The selectivity to styrene oxide and the efficiency of H2O2 for the epoxidation can be improved by adding H2O2 slowly to keep the H2O2 concentration low during the reaction. As compared with the DHT catalyst, the TIE catalyst shows a much poorer performance for the epoxidation of styrene. It is suggested that the atomically isolated iron sites account for the epoxidation reaction with hydrogen peroxide. The iron cations incorporated inside the framework of MCM-41 do not leach during the reaction, whereas the small iron oxide clusters leach out into the liquid phase and do not contribute to the catalytic reaction.

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.