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Abstract: Using a postsynthesis grafting method, 3-aminopropyltriethoxysilane (3-APTS) was functionalized over silica gel and mesoporous silica materials like SBA-15 and MCM-41. Vanadyl cations were then immobilized over the functionalized amino groups of the silica samples and used as a catalyst in the liquid-phase oxidation reaction of cyclohexane. Elemental analysis, PXRD, TEM, N2 adsorption–desorption isotherms, FTIR, and MAS NMR, UV–vis, and EPR techniques were used to characterize the developed materials. Characterization results suggest that the percentage of 3-APTS grafting depends on the number of isolated and geminal silanol sites of the support material, the solvents used during the grafting reactions, and the sample pretreatment conditions. We found that using toluene as the dispersing medium and Si-MCM-41 as a support provides the maximum amount of amine functionalization, and thereby the highest percentage of vanadium immobilization. Catalytic activity and metal leaching studies show that vanadium-immobilized mesoporous solids are more active and stable than the silica gel-functionalized vanadium catalyst and a framework-substituted V-MCM-41 catalyst. The enhanced activity and stability of the immobilized vanadium catalysts compared with the V-MCM-41 and silica gel samples are attributed to the active metal site isolations, as well as to the spatial restrictions imparted from the concave silica surfaces of the mesoporous solids rather than the convex silica surfaces of the silica gel sample. [Copyright &y& Elsevier]

Abstract: Vanadium-containing ethane–silica hybrid mesoporous silsesquioxane materials (V-HMM) with uniform hexagonal arrangement were prepared using C18-, C16- and C14-alkyl trimethyl ammonium (ATMA) surfactants under basic conditions. The materials were characterized by PXRD, N2 adsorption–desorption, UV–Visible spectroscopy, Raman, 29Si, 13C and 51V solid-state MAS NMR, TEM and SEM techniques. The characterization techniques revealed that the structural ordering, morphology as well as the percentage of metal incorporation depends strongly on the hydrophobic chain length of the surfactant. PXRD, electron microscopy and N2 adsorption–desorption analysis confirmed that the original hexagonal structure of the material is maintained after vanadium substitution. UV–Visible, 51V NMR and Raman analysis certified that vanadium exists in a highly dispersed state and had tetrahedral coordination with the support surface. Liquid-phase epoxidation reaction of styrene using aqueous H2O2 and TBHP as oxidants, showed that the hybrid materials were highly active and more stable than conventional vanadosilicates. The high catalytic activity and improved epoxide selectivity of the V-HMM samples is related to the more hydrophobic environment inside the pore channels than the silica channels in V-MCM-41. [Copyright &y& Elsevier]

Abstract: A series of vanadium-substituted mesoporous materials were synthesized hydrothermally with the use of two commonly used silica sources, fumed silica and tetra ethyl orthosilicate. The extent of mesopore structural ordering was confirmed from X-ray diffraction, N2 physisorption, SEM, and TEM, and the presence and nature of vanadium species inside the framework of the MCM-41 matrix was confirmed in detail with the use of various characterization techniques like FT-IR, 29Si MAS NMR, DRUV–vis, EPR, 51V MAS NMR, and Raman analysis. It is deduced from the above characterization techniques that, regardless of the silica source, vanadium is incorporated into the silica framework and thereby increases the structural ordering and wall thickness of the mesoporous material. Thermal and hydrothermal studies performed over the V-MCM-41 catalysts show that the Sih name="sbnd" />Si inorganic backbone from a fumed silica source is more resistant to severe thermal treatments and hydrolysis than the tetraethyl orthosilicate-synthesized catalysts. Spectroscopic characterization reveals the existence of easily accessible isolated tetrahedral vanadium sites on V-MCM-41 catalyst prepared from fumed silica catalyst, whereas the sample obtained from a tetraethyl orthosilicate silica source shows vanadium in more disordered sites. Catalytic results show that both catalysts display excellent activity toward the epoxidation reaction of bulkier olefins, and the exceptional activity of the fumed silica catalyst may arise from the more isolated tetrahedral sites and the complementary textural characteristics, which may facilitate the easy access of substrate to the isolated framework metal sites. [Copyright &y& Elsevier]

Heterogeneous carbometallated palladacycle catalysts have been synthesized by treatment of palladation reagents with 3-hydroxypropyltriethoxysilane-incorporated MCM-41 (OH-M) under mild reaction conditions. Palladation over organo-functionalized MCM-41 and organo-functionalized silica has been performed and it was found that the spatial confinement induced by the pore walls of organo-functionalized MCM-41 forces the propyl group to cyclize in the presence of an electrophilic metal center which is found to be much lower in organo-functionalized silica. Optimization studies, including change in Pd concentration in solution, different palladation reagents in palladation reactions such as Li2PdCl4, Pd(OAc)2, effect of base, palladation temperature, and different solvents (methanol, chloroform, and acetone used as reaction medium), have been performed over organo-functionalized MCM-41 for obtaining better results of palladation. A number of characterization techniques have been exploited to support the formation of a palladacycle complex inside the pores of mesoporous materials. The Heck alkenylation reaction, which is universally accepted as a sharpening stone of palladium catalysts, was set as a model reaction to evaluate the catalytic activity of all the catalysts investigated in this study. The heterogeneity of the catalyst has also been studied. [Copyright &y& Elsevier]

A new aliphatic C-metallated palladacycle has been prepared in the pores of 3-hydroxypropyl triethoxysilane functionalized MCM-41 and has been found to be a superior recyclable catalyst for Heck reaction. The thermal stability of the palladated material was found to be higher than that of the nonpalladated starting material. [ABSTRACT FROM AUTHOR]

Abstract: Novel bifunctional periodic mesoporous silicas having high content of organic groups in the pore channels and chromium in the frame wall has been synthesized by direct co-condensation method, using organo trialkoxysilanes (chloro propyl, vinyl, methyl), chromium nitrate and tetraethyl orthosilicate, in presence of cetyltrimethyl ammonium surfactants. The obtained materials show one main peak in the XRD patterns up to a molar ratio of 1:1 between TEOS and organosilane in the synthesis gel and N2 adsorption–desorption analysis shows that the mesopore structure remains intact after the surfactant removal process. Among the organosilanes, chloro propyl and vinyl pendant chromium samples shows a shift in the main peak to higher 2-theta values with a corresponding decrease in pore volume and pore diameter, with the percentage of organosilane functionalization. Small-pore silicas and chromium silicas can be prepared from the large pore mesoporous MCM-41, by effectively removing the organic groups by calcination. By this method, the pore size of the material can be tailored into the super-microporous region, without changing the chain length of the surfactant used in the assembly process. The shrinkage in pore size is dependent on the nature and percentage of the organic pendant groups that the chloro propyl and vinyl pendant mesoporous materials show the maximum pore size shrinkage than the small chain length methyl units. Because of the tailorable pore size and with better textural characteristics, chromium-silica materials find applications in the field of shape selective heterogeneous catalysis, as demonstrated in the oxidation reaction of cyclohexane, than the conventional metal-containing mesoporous materials. [Copyright &y& Elsevier]

Abstract: Vanadium-containing ethane-silica hybrid mesoporous material was synthesized using 1,2-bis(triethoxysilyl)ethane as the silica source and octadecyltrimethyl ammonium bromide as the structure orientor. The material was characterized systematically by XRD, N2 adsorption–desorption, UV–Vis and NMR techniques. The organo vanadosilicate material was used as catalyst in the liquid phase epoxidation reaction of cis-cyclooctene, using H2O2 as well as TBHP as oxidants. The hybrid material was found to be more catalytically active and stable than the conventional vanadium-containing mesoporous catalyst, V-MCM-41. [Copyright &y& Elsevier]

Abstract: Tin-containing ordered mesoporous silica materials (Sn-OMS) were synthesized by two different routes, viz. by the direct hydrothermal method (Sn–MCM-41, Sn–MCM-48) and by the grafting method (Sn/MCM-41, Sn/MCM-48, Sn/SBA-15). The materials were characterized in detail by ICP-OES analysis, XRD, FTIR, N2 adsorption–desorption, SEM and UV–vis analysis. The catalytic activity of the tin-modified mesoporous materials was ratified in the Meerwein–Ponndorf–Verley reduction of carbonyl compounds using secondary alcohols (2-butanol and 2-propanol) as hydrogen transfer agents. A comparison of catalytic activities of tin-containing mesoporous materials prepared by the two routes, dictates that tin-grafted mesoporous materials show higher catalytic activity than the tin incorporated mesoporous catalysts, even though both the materials had similar tin loadings. Among the tin-grafted catalysts, the samples prepared using the tin precursor, Me3SnCl, showed better activity than the other precursors Bu3SnCl, Ph3SnCl and Ph2SnCl2 and among the mesoporous supports, Si–MCM-41 shows better catalytic results than the other supports like Si–MCM-48 and Si–SBA-15. [Copyright &y& Elsevier]

Abstract: Aluminium-containing ethane-silica hybrid mesoporous materials having ethane groups in the frame wall positions are synthesized using aluminium isopropoxide as well as aluminium nitrate as the aluminium sources. The materials were characterized in detail using powder XRD, N2 adsorption–desorption, SEM, TEM, TG-DTG, TPD, 29Si, 13C and 27Al MAS NMR techniques. Characterization techniques revealed that aluminium isopropoxide was the appropriate source for the synthesis of organo aluminosilicas on considering the structural ordering, acidity as well as the percentage of aluminium incorporation into the ethane bridge. 27Al MAS NMR displays aluminium as tetrahedrally coordinated in both the aluminium-containing organosilicas. Unlike the conventional EtOH–HCl template extraction process, in the present studies, we had used EtOH–NH4OH as the surfactant-extracting medium and chemical analysis results suggest that using this procedure the extent of dealumination can be greatly reduced. XRD and nitrogen physisorption studies further proved that the materials are hydrothermally stable, that the ordered pore channels retains its structure even after 150h reflux in boiling water, while the conventional Al-MCM-41 catalyst collapsed its mesostructure after 50h reflux in water. The improved hydrothermal stability of the hybrid materials, even in presence of sodium ions, is attributed to the thick pore walls as well as due to the presence of hydrophobic bridging ethane groups in the wall positions. [Copyright &y& Elsevier]

Abstract: Hydrothermally stable periodic mesoporous organosilicas with spherical as well as wormlike frame structures were synthesised by two different synthesis routes using the silsesquioxane precursor, 1,2-bis (triethoxy silyl) ethane (BTEE) and surfactant octadecyl trimethyl ammonium (ODTA), under basic conditions. The materials were characterized by PXRD, SEM, TEM, N2 adsorption–desorption, FT-IR, 29Si MAS NMR, 13C CP MAS NMR and TG-DTA techniques. Characterization techniques revealed that the morphology of the hybrid material prepared from pure silsesquioxane precursor resulted in spherical particles while a combination of tetra ethyl orthosilicate and 1,2-bis (triethoxy silyl) ethane (90:10 ratio) resulted in materials having wormlike structures. Hydrothermal stability of the hybrid material was evaluated by refluxing the sample under boiling water for various time periods and was compared with that of a periodic mesoporous silica material, Si-MCM-41. Results showed that the hybrid material is stable up to 100h in boiling water, with the existence of d 100 peak, while the mesopore structure of Si-MCM-41 get destroyed even after a 12h reflux time. The improved hydrothermal stability of the hybrid material is related to the more hydrophobic environment induced inside the pore channels, due to the presence of integrating ethane groups in the wall channels. [Copyright &y& Elsevier]

Abstract: Vanadium-substituted ordered mesoporous silicates (V-OMS) were synthesized hydrothermally using two common silica sources, viz. fumed silica and tetraethyl orthosilicate, and their surface properties and catalytic activities were evaluated in the liquid phase oxidation of 1-napthol using aqueous H2O2 as an oxidant. The catalysts were characterized by XRD, N 2 adsorption–desorption, DRUV–vis and TPR to evaluate the mesostructural ordering and the local environment of vanadium in the MCM-41 matrix. Characterization data of the fresh calcined catalysts reveal a more ordered hexagonal structure for the V-MCM-41 catalyst prepared by using tetraethyl orthosilicate as the silica source while spent catalyst showed that the material is less stable than the V-MCM-41 catalyst prepared by using fumed silica as the silica source. Further, the observed differences in the selectivity behavior of extracted and calcined forms of both vanadium catalysts shows that the treatment conditions had a decisive role in the formation of extra framework metal species and further in the mesoscopic structural ordering. [Copyright &y& Elsevier]

Abstract: Ethane bridged mesoporous organosilicas and MCM-41 having sulfonic acid groups in the pore channels were prepared by co-condensation method as well as grafting method, using 3-mercaptopropyltriethoxysilane (3-MPTS) as the sulfur precursor. TEM and N2 sorption isotherm analysis revealed that the mesoporous structural ordering is retained after the functionalization and modifications of organic groups while FT-IR, Raman, XPS and solid-state 13C CP MAS NMR shows the presence of sulfonic acid groups and the stability of the mesoporous framework. The catalytic activity of the developed materials was evaluated in the liquid phase Claisen–Schmidt condensation reaction of acetophenone with benzaldehyde, to probe the effect of mesoporous support surfaces as well as the role of preparation methods. Results showed that sulfonic acid functionalized ethane–silica samples were more active, selective and stable than the conventional sulfonic acid containing mesoporous catalysts. [Copyright &y& Elsevier]