03125nas a2200241   4500008004100000022001400041245009700055210006900152260007300221300001200294490000800306520222500314653003402539653002902573653003902602653001402641653002602655100001302681700002202694700001802716700002002734856012902754       2007                        eng d  a1387-181100aDirect hydrothermal synthesis of mesoporous Sn-SBA-15 materials under weak acidic conditions0 aDirect hydrothermal synthesis of mesoporous SnSBA15 materials un  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcMAR  a210-2260 v1003 a<p>A direct synthetic route for the preparation of Sn-SBA-15 materials with n(Si)/n(Sn), ratios ranging from 100 to 10 under milder acidic conditions than normally employed for the preparation of Si-SBA-15 is reported. The changes in the pH conditions of the gel were made through an adjustment of the molar ratio of n(H2O) to n(HCl) (&lt; 1 pH &lt; 2) during preparation. The samples prepared under three different acidic conditions have been characterized by various techniques. An expansion of the lattice (powder XRD) and an increase in mesopore area (low temperature N-2 adsorption) indicate that the hexagonal structure of the SBA- 15 is maintained with no loss of long range ordering. The UV-vis reflectance spectra of Sn-SBA-15 samples show the presence of Sn4+ ions both in tetrahedral and octahedral environment. Si-29 MAS NMR spectra of samples prepared under an intermediate acid condition show the presence Of Q(3) and Q(4) species. Their ratio increases with a decrease in tin content. The presence of Si in (2Si, 2Sn) i.e., Q(2) environment may point to incorporation of considerable Sn4+ ions in tetrahedral positions. Sn-Mossbauer spectroscopic studies reveal that Sn2+ species form upon reductive treatments and can probably be stabilized in the pore wall upon reoxidation. This to some extent is an indication of the formation and stabilization of Si-O-Sn-O-Si linkages in Sn-SBA-15. A progressive increase in the pH of the medium (increasing the n(H2O) to n(HCl), ratio) results in the location of Sn4+ ions, (a) at the surface of the mesopores (surface of the corona region) as a thin film of SnO2 or small aggregates (loss in mesopore area) depending on the concentration of Sn; (b) at the walls of the mesopore structure, substituting Si4+ ions (some lattice expansion and tetrahedral Sn4+ ions); and/or (c) as a part of the corona region, neutralizing the resulting Si-OH groups (a loss of micropore area and octahedral Sn4+ ions). The studies reveal that the method of preparation, n(H2O)/n(HCl) ratio and the n(Si)/n(Sn) ratio (concentration of SnCl4) of the gel significantly influence the type of tin species in the resulting Sn-SBA-15 samples. (c) 2006 Elsevier Inc. All rights reserved.</p>10adirect synthesis of Sn-SBA-1510aSi-29 and Sn-119 MAS-NMR10aSn-mossbauer spectroscopic studies10aSn-SBA-1510atin-mesoporous silica1 aShah, P.1 aRamaswamy, A., V.1 aLazar, Karoly1 aRamaswamy, Veda  uhttps://library.ncl.res.in/content/direct-hydrothermal-synthesis-mesoporous-sn-sba-15-materials-under-weak-acidic-conditions02476nas a2200241   4500008004100000022001400041245009600055210006900151260007500220300001200295490000700307520158400314653002501898653002801923653002501951653002401976653002702000100002002027700001802047700001802065700002202083856012902105       2008                        eng d  a1571-101300aSynthesis, characterization and catalytic activity of Sn-SBA-15 mesoporous molecular sieves0 aSynthesis characterization and catalytic activity of SnSBA15 mes  a233 SPRING ST, NEW YORK, NY 10013 USAbSPRINGER/PLENUM PUBLISHERScDEC  a283-3090 v123 a<p>Our recent reports on the synthesis of Sn-incorporated mesoporous SBA-15 materials have been reviewed. The preparation of the samples with different Si/Sn ratios followed two procedures, the first is the post-synthesis modification of SBA-15 by impregnation with Sn chloride or acetate, and the second is the direct method in which Sn chloride was introduced in to Si precursor along with amphiphilic triblock copolymer, while varying the ratio of the synthesis gel. Detailed characterization of the Sn-SBA-15 samples by a variety of techniques shows how the synthesis procedures influence the properties of the samples that reflect on the differences in (a) the structural features, (b) morphology and textural properties, such as the pore characteristics, (c) the possible location of Sn4+ ions in the meso silica structure and their reducibility, (d) the nature of the Sn species and their the coordination sphere and (e) the acid-base characteristics. We developed a possible model for the localization of Sn species in SBA-15 pore structure for different conditions of preparation. This report includes our investigations on the catalytic properties of these Sn-SBA-15 samples in 3 industrially important reactions, viz., trans-esterification of diethyl malonate, synthesis of nopol by Prins condensation of beta-pinene with para-formaldehyde and the epoxidation of norbornene. In each of this reaction, while demonstrating the catalytic role of Sn species, we show that the requirement of the type and the environment of Sn species are different for these reactions.</p>10amesoporous materials10aProperties of Sn-SBA-1510aSn-containing SBA-1510aSn-SBA-15 catalysts10aSynthesis of Sn-SBA-151 aRamaswamy, Veda1 aShah, Pallavi1 aLazar, Karoly1 aRamaswamy, A., V.  uhttps://library.ncl.res.in/content/synthesis-characterization-and-catalytic-activity-sn-sba-15-mesoporous-molecular-sieves-0