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Effect of post-calcination thermal treatment on acid properties and pores structure of a mesoporous niobium–tungsten oxide was examined. Mesoporous Nb–W oxides treated by high temperature calcination from 673 up to 873 K exhibited a significant increase in pore size from 4.8 to 9.2 nm, a decrease in pore volume, surface area and acid amount, while the acid strength and density remained almost constant. A remarkable improvement in acid catalysis was observed for Friedel–Crafts alkylation and hydrolysis of disaccharide where the turnover frequency for both reactions increased continuously with calcination temperature.

Ta 2 O 5 layer was prepared onto SBA-15 (Ta 2 O 5 /SBA-5) with Ta ethoxide precursor. The surface properties of Ta 2 O 5 /SBA-5 was the same as those of mesoporous Ta 2 O 5 , possessing electron accepting sites and hydrophobicity, but the structural stability upon thermal treatment was improved due to the presence of SBA-5. The drastic blue shift in UV–vis absorption band was observed when the phase of Ta 2 O 5 became thinner. Accordingly, band gaps of Ta 2 O 5 samples increased from 4.0 (nonporous Ta 2 O 5 ) to 4.3 eV (mesoporous Ta 2 O 5 , 2.3 nm wall thickness), and further increased to 4.9 eV for thin-layered Ta 2 O 5 /SBA-5 (0.5 nm Ta 2 O 5 layer). Thus, stable activity for photocatalytic water decomposition was not observed over thin-layered Ta 2 O 5 /SBA-5.

Several porous Nb x Mo 10− x mixed oxides prepared from NbCl 5 and MoCl 5 in the presence of block copolymer surfactant Pluronic P-123 were examined as potential solid acid catalysts. Amorphous mesoporous structures were observed in samples with x from 10 to 9, whereas samples with higher Mo concentrations ( x = 3–8) formed large pores by inter-particle voids and a non-porous structures with crystallized molybdenum oxide (MoO 3 ) were observed in samples with x from 0 to 2. The acid strength increased with increasing the Mo content in Nb x Mo 10− x oxides, which was determined by NH 3 temperature-programmed desorption (NH 3 -TPD) and Fourier transform infrared (FT-IR) spectroscopy using pyridine as a probe molecule. Porous Nb 3 Mo 7 oxide exhibited the highest acid-catalytic activity for the Friedel–Crafts alkylation of anisole due not only to mole ratio of Nb/Mo but also to pore structure.

The cubic Ia -3 d mesoporous silica with ordered large pores was synthesized from tetraethoxysilane (TEOS) and a small amount of 3-mercaptopropyltorimetoxysilane (MPTS) as the silica sources under the acidic conditions by using triblock copolymer P123 (EO 20 PO 70 EO 20 ) as a surfactant. After removal of the surfactant by the solvent extraction method, mercaptopropyl (MP) group (–CH 2 CH 2 CH 2 SH) remained inside pores with a slight loss. The pore diameter of this mesoporous silica was about 5 nm. After converting the MP group to sulfopropyl (SP) group (–CH 2 CH 2 CH 2 SO 3 H) by the oxidation with H 2 O 2 , the amount of organic group was significantly reduced. However, it was possible to introduce additional organic groups by post-synthetic grafting. It was also possible to graft both MP and SP groups at the same time, and cooperative effect was observed in the acid-catalyzed condensation reaction of phenol with acetone. More organics were immobilized to the multi-dimensional cubic Ia -3 d structure than the one-dimensional 2d-hexagonal structure. The catalyst having both SH and SO 3 H groups showed much higher selectivity for bisphenol A than Amberlyst 15 and Nafion SAC-13, which could be explained by the SH group-assisted mechanism.

The epoxidation of cyclopentene has been carried out over titanosilicate catalysts of Ti-Beta, TS-1 and Ti-MWW. Ti-MWW exhibited the highest cyclopentene conversion and epoxide selectivity with either H2O2 or tert-butyl hydroperoxide as an oxidizing agent. The cyclopentene conversion depended greatly on the post treatment conditions. Acid-treated but uncalcined Ti-MWW gave cyclopentene conversion twice as high as the calcined one, while the epoxide selectivity was maintained at high levels in both cases. Various techniques such as XRD, UV–vis, 29Si MAS NMR, N2 adsorption and liquid-phase adsorption, and chemical analyses have verified consistently that the acid treatment removed the organic species located between the layers of MWW sheets, which made the interlayer entrance open and easily accessible to bulky molecules. Nevertheless, a further calcination led to a complete interlayer dehydroxyaltion and made the catalyst to be more effective for the epoxidation of linear alkenes but less active for the epoxidation of cyclic ones.

The influence of acidity, alkyl chain length of alcohols, synthesis temperature and time on the molecular sieve synthesis by adding alcohols to the system for the SBA-1 synthesis were studied. Upon increasing the concentration of alcohols (C m H 2 m +1 OH) in the mixture of tetraethyl orthosilicate (TEOS), cetyltriethylammonium bromide (CTEABr), HCl and H 2 O, highly ordered P 6 3 / mmc and p 6 mm phases were formed when m = 2 and 3 ≤ m ≤ 6, respectively. The amount of HCl was an important factor for the phase-selection under acidic conditions.

MWW type titanosilicate, Ti-MWW, has been synthesized by the dry-gel conversion (DGC) method, and its physicochemical properties and catalytic performance in the liquid-phase epoxidation of alkene have been compared with that of hydrothermally synthesized (HTS) Ti-MWW. The roles in the crystallization of silica source, alkali cation, cyclic amine as a structure-directing agent (SDA), and boric acid structure-supporting agent have been investigated. The crystallization of Ti-MWW did not occur for the dry gels free of boric acid, but was feasible at a Si/B molar ratio as high as 12 in marked contrast to the ratio of 0.75 required in the hydrothermal synthesis. The sodium as a mineralization agent was not necessary and on the contrary inhibited the crystallization particularly at a high content. The seeding technique using deboronated MWW effectively accelerated the crystallization speed and reduced the amount of boric acid required. As-synthesized Ti-MWW-DGC lamellar precursors contained both tetrahedral and octahedral species but the latter was selectively removed by acid treatment. Ti-MWW-DGC catalysts showed lower intrinsic activity than Ti-MWW-HTS in the epoxidation of hex-1-ene with hydrogen peroxide probably because the crystal size of the former was 10–20 times as large as that of the latter and then imposed significant diffusion problems for both the substrates and the products.

The direct gas-phase oxidation of propylene with molecular oxygen was carried out over Ti–MCM-41 impregnated with metal nitrates to produce propylene oxide (PO) selectively. The effects of Ti-loading on MCM-41, nitrate additives, acid treatment of the support, and the presence of molecular oxygen were investigated. The PO yield increased with increasing Ti content of Ti–MCM-41 and reached a maximum at an optimum Si/Ti ratio of 100. Calcium nitrate was the most suitable additive among various nitrates of alkali and alkaline earth metals investigated, and the acid treatment of Ti–MCM-41 effectively improved its catalytic performance for the PO formation. The presence of both nitrate and molecular oxygen was essential for the PO formation. A synergetic mechanism between the Ti species and metal nitrate was proposed to be responsible for the selective formation of PO.

Highly dispersed titanium oxide catalysts have been prepared within zeolite cavities as well as in the zeolite framework and utilized as photocatalysts for the reduction of CO 2 with H 2 O to produce CH 4 and CH 3 OH at 328 K. In situ photoluminescence, ESR, diffuse reflectance absorption and XAFS investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species play a significant role in the reduction of CO 2 with H 2 O with a high selectivity for the formation of CH 3 OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH 4 , being similar to reactions on the powdered TiO 2 catalysts. Ti-mesoporous molecular sieves exhibit high photocatalytic reactivity for the formation of CH 3 OH, its reactivity being much higher than the powdered TiO 2 catalysts. The addition of Pt onto the highly dispersed titanium oxide catalysts promotes the charge separation which leads to an increase in the formation of CH 4 in place of CH 3 OH formation.

Titanium oxide species included within the framework of mesoporous zeolites (Ti-MCM-41 and Ti-MCM-48) prepared by a hydrothermal synthesis exhibited high and unique photocatalytic reactivity for the reduction of CO2 with H2O at 328 K to produce CH4 and CH3OH in the gas phase. In situ photoluminescence, diffuse reflectance absorption, ESR and XAFS investigations indicated that the titanium oxide species are highly dispersed within the zeolite framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species played a significant role in the reduction of CO2 with H2O exhibiting a high selectivity for the formation of CH3OH.

Manganese tetraphenylphorphyrin complex fixed on imidazole-modified silica exhibits fair catalytic activity for cyclohexane oxidation by hydrogen peroxide. Immobilization of the porphyrin complex could result in the prevention of the formation of μ-oxo dimers, increasing the catalytic capability. Turnover numbers for cyclohexane oxidation are greatly improved by decreasing metal loadings, suggesting the importance of site isolation of the metal complexes. Rather high loading of imidazolyl group is required since its ligation to Mn was fully effected when imidazolyl group in large excess of Mn is present, as shown in the change in the diffuse reflectance spectra with imidazolyl/Mn ratio.