Ruihua Gao

Highly active and green aminopropyl-immobilized phosphotungstic acid on mesocellular silica foam for the O-heterocyclization of cycloocta-1,5-diene with aqueous H2O2

The heteropoly phosphotungstic acid, H3PW12O40 (HPW), was successfully immobilized on the surface of MCF, SBA-15 and MCM-41 by means of chemical bonding to aminosilane groups. The as-obtained materials were characterized by N2 sorption, TEM, XRD, FT-IR, 13C-, 29Si-, 31P-MAS NMR and XPS. Characterization results suggest that the surface area decreased after grafting amino groups to silica. The as-prepared HPW-NH2-MCF is highly efficient in the O-heterocyclization of cycloocta-1,5-diene (COD) to 2,6-dihydroxy-9-oxabicyclo[3.3.1] nonane (1) and 2-hydroxy-9-oxabicyclo [3.3.1] nonane-6-one (2) with a COD conversion of 100% and (1 + 2) selectivity up to 98%. It is worth mentioning that this material could be reused six times without any significant loss of activity and selectivity. The good stability can be attributed to the strong interaction between the amino groups on the surface of MCF and HPW anions.

A green process for the epoxidation of dicyclopentadiene with aqueous H2O2 over highly efficient and stable HPW-NH2-SBA-15

Dicyclopentadiene dioxide (2) was synthesized using an economic and green reaction by the direct oxidation of dicyclopentadiene (DCPD) with aqueous H2O2 over tungstic acid and aminopropyl-immobilized phosphotungstic acid on SBA-15, which was successfully obtained by the immobilization of the supported heteropolyacid (HPW) on the surface of the ordered mesoporous silica, SBA-15, by means of chemical bonding to aminosilane groups. The as-obtained materials were characterized by N2 sorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), 31P-magic angle spinning (MAS) NMR and Raman spectroscopy. The 16% HPW-NH2-SBA-15 is highly efficient in the reaction with a DCPD conversion of 100% and (2) selectivity up to 97%. It is interesting that this material could be reused six times without any significant loss of activity and selectivity. The good stability can be attributed to the strong interaction between the amino groups on the surface of SBA-15 and HPW anions.

A green process for O-heterocyclization of cycloocta-1,5-diene by peroxotungstic species with aqueous H2O2

The hydroxy- and carbonyl-derivatives of 9-oxabicyclo[3.3.1]nonane have been synthesized through an economic and green catalytic reaction between cycloocta-1,5-diene (COD) and aqueous H2O2 with tungstic acid as the catalyst. This process has advantages from the viewpoint of green chemistry, in that the aqueous H2O2 is used as the green oxygen donor, the only by-product of H2O2 is water and the tungstic acid catalyst can also be easily recovered. The excellent yields of the object products (1 and 2) (see Scheme 1) are reached easily under mild reaction conditions.

Thermal oxidative etching method derived graphitic C3N4: highly efficient metal-free catalyst in the selective epoxidation of styrene

A series of g-C3N4 nanosheets were synthesized by thermal oxidation with long time heating and etching. With an increase in heating time from 1.0 to 3.0 h, the g-C3N4 nanosheet was obtained with a thinner layer thickness, larger BET surface area and higher graphic nitrogen ratio. As a metal-free heterogeneous catalyst, the g-C3N4 NS-3 h nanosheets show a superior catalytic performance for the epoxidation of styrene to styrene oxide than that of the bulk g-C3N4 and other recently reported metal-free materials. The higher activity of the g-C3N4 NS-3 h synthesized by long time thermal oxidative etching might be ascribed to the enlarged specific surface, pore volume and higher graphic nitrogen ratio with the loose and soft laminar morphology. The graphitic nitrogen species play a key role in the catalytic reaction based on a good linear correlation between the content of these species and the activity results. The g-C3N4 nanosheets are very stable and can be reused 5 times without obvious loss of catalytic activity.

Tungsten containing materials as heterogeneous catalysts for green catalytic oxidation process

This chapter provides a comprehensive description of the recent advances in the field of tungsten-containing heterogeneous catalysts for green catalytic oxidation processes. This chapter contains three sections. The first exhibits the advances in the pristine tungsten-based catalysts for the green catalytic oxidation process. The second highlights various green catalytic oxidation reactions with tungsten-based catalysts supported on different carriers. The third illustrates the existing problems and outlook for the tungsten-based catalysts applied in the green catalytic oxidation reactions. All these contributions provide a proper guide and overview to tungsten-based catalysts for the sake of the better development of highly efficient green oxidation catalytic systems.