Maxim S. Mel'gunov

Hybrid Polyoxotungstate/MIL-101 Materials: Synthesis, Characterization, and Catalysis of H2O2-Based Alkene Epoxidation

Polyoxotungstates [PW(4)O(24)](3-) (PW(4)) and [PW(12)O(40)](3-) (PW(12)) have been inserted into nanocages of the metal organic framework MIL-101. The hybrid materials PW(x)/MIL-101 (x = 4 or 12) containing 5-14 wt % of polyoxotungstate have been obtained and characterized by elemental analysis, N(2) adsorption, FT-IR, Raman, and (31)P NMR MAS spectroscopic techniques. Their catalytic performance was assessed in the selective oxidation of alkenes with aqueous hydrogen peroxide under mild reaction conditions ([H(2)O(2)] = 0.1-0.2 M, 50 degrees C, MeCN). PW(x)/MIL-101 enclosing 5 wt % of polyoxotungstate demonstrated fairly good catalytic activities in the epoxidation of various alkenes (3-carene, limonene, alpha-pinene, cyclohexene, cyclooctene, 1-octene), the turnover frequencies (TOF) and alkene conversions were close to the corresponding parameters achieved with homogeneous PW(x). For the oxidation of substrates with aromatic groups (styrene, cis- and trans-stilbenes), a higher level of olefin conversion was attained using PW(12)/MIL-101. Moreover, confinement of PW(12) within MIL-101 nanocages allowed us to reach higher epoxide selectivities at higher alkene conversions. The hybrid PW(x)/MIL-101 materials were stable to leaching, behaved as true heterogeneous catalysts, were easily recovered by filtration, and reused several times with the maintenance of the catalytic performance.

Magnetically separable titanium-silicate mesoporous materials with core–shell morphology: synthesis, characterization and catalytic properties

The preparation and characterization (XRD, N2 adsorption, TEM, EDX, DRS-UV) of a novel catalytic material Ti-SMCMS (solid magnetic core–mesoporous shell) is reported. The material has quasi spherical particles with an ordered mesoporous silicate shell containing isolated Ti atoms and a silica core which, in turn, comprises superparamagnetic iron oxide nanoparticles. The magnetic kernels are embedded in the nonporous silica core and, thus, are completely protected from ambient medium. The material was found to combine the advantages of high activity and selectivity in H2O2-based selective oxidations with the merits of an easy magnetic separation from the reaction mixture.

User-friendly synthesis of highly selective and recyclable mesoporous titanium-silicate catalysts for the clean production of substituted p-benzoquinones

Mesoporous titanium-silicates have been prepared following the evaporation-induced self-assembly (EISA) methodology and characterized by elemental analysis, XRD, N2 adsorption, SEM, DRS UV–Vis and Raman techniques. The use of acetylacetone during synthesis allowed the formation of highly dispersed dimeric and/or small oligomeric Ti species, within the mesostructured silica network, to be realized. The materials catalyse oxidation of alkylsubstituted phenols to corresponding p-benzoquinones with 100% selectivity using the green oxidant – 30% aqueous hydrogen peroxide. The titanium-silicates prepared by the convenient and versatile EISA-based procedure reveal the true heterogeneous nature of the catalysis and do not suffer from titanium leaching. They show advantages over other types of mesoporous Ti,Si-catalysts, such as TiO2–SiO2 mixed oxides and grafted Ti/SiO2, in terms of the catalyst stability and reusability.

Textural and structural properties of Al-SBA-15 directly synthesized at 2.9 < pH < 3.3 region

Abstract Implantation of Al in a carcass of SBA-15 silicate directly during its synthesis at pH in a range of 2.9-3.3 using sodium silicate and aluminum sulfate as precursors results in formation of a well organized hexagonally structured mesophase. The effect of mesophase perfection improvement due to Al implantation is reported. The obtained materials demonstrate high thermohydrostability and mechanical strength.