@article { ISI:000230396800004, title = {Ti-oxo radicals and product selectivity in olefin oxidations over titanosilicate molecular sieves}, journal = {Zeitschrift f{\"u}r Physikalische Chemie International Journal of Research in Physical Chemistry and Chemical Physics}, volume = {219}, number = {7}, year = {2005}, month = {JUL}, pages = {905-920}, publisher = {OLDENBOURG VERLAG}, type = {Article}, address = {LEKTORAT MINT, POSTFACH 80 13 60, D-81613 MUNICH, GERMANY}, abstract = {

The O-O bond of Ti-oxo species (Ti-peroxo, Ti-hydroperoxo or Ti-superoxo) generated on titanosilicate molecular sieves contacted with H2O2 cleaves either heterolytically or homolytically. While the former type of O-O cleavage (generating non-radical reactive oxygen intermediates) leads to selective epoxide products, the latter (generating reactive oxygen radical intermediates, O-2(-center dot) and HOOcenter dot) results in non-sclective, allylic oxidation products in cyclohexene oxidation. These radicals were detected using EPR spin trapping techniques 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was used as the spin trap. Radical quenchers like hydroquinone suppressed their concentration and enhanced epoxide selectivity.

}, keywords = {cyclic voltammetry of titanosilicates, EPR-spin trap experiments, Molecular sieves, oxidations, product selectivity, reactive oxygen species, titaniunz-oxo radicals, Titanosilicates}, issn = {0942-9352}, doi = {10.1524/zpch.219.7.905.67088}, author = {Shetti, VN and Srinivas, D and Ratnasamy, P} } @article { ISI:000264437500002, title = {Selective oxidations over zeolite- and mesoporous silica-based catalysts: selected examples}, journal = {Catalysis Today}, volume = {141}, number = {1-2}, year = {2009}, note = {18th National Symposium and Indo-US Seminar on Catalysis, Indian Inst Petroleum, Dehradun, INDIA, APR 16-18, 2007}, month = {MAR}, pages = {3-11}, publisher = {Catalysis Soc India; Petrotech Soc; Indo US Sci \& Technol Forum}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Selective oxidation of hydrocarbons/terpenes in the liquid phase are reported over three categories of zeolite- and mesoporous silica-based catalysts: (1) transition metal complexes (metal phthalocyanines, copper acetate dimers and Co/Mn acetate trimer) encapsulated in zeolite-Y, (2) transition metal complexes (Mn-Salen), grafted on SBA-15, and (3) transition metal ions in framework positions of zeolites and mesoporous molecular sieves like Ti-silicates. Upon heterogenization, the metal complexes exhibited enhanced catalytic acitivity/selectivity. The causes for the enhanced catalytic activity/product selectivity have been explored. Dimer formation (copper acetate) or geometric distortion in the zeolite cavities (metal phthalocyanines) and consequent changes in energy levels and redox potentials are shown to modify the catalytic activity (in the selective oxidation of hydrocarbons) of the encapsulated metal complexes. In the case of Mn-Salen grafted on SBA-15, increasing the acidity of the siliceous surface (by -SO(3)H groups, for example) leads to a more facile reduction of the Mn ions and, thereby, enhanced catalytic activity in the selective epoxidation of limonene. When Ti ions are introduced in framework positions, reactive metal-oxo species are formed on contact with H(2)O(2) or O(2), Which influence the mode of O-O cleavage (heterolytic/homolytic) and product selectivity. The structure-function relationships in these catalysts are reported. (c) 2008 Elsevier B.V. All rights reserved.

}, keywords = {Mn-Salen, Oxidation of hydrocarbons and limonene, Reactive oxo species, Selective oxidation, Titanosilicates, Zeolite-encapsulated metal complexes}, issn = {0920-5861}, doi = {10.1016/j.cattod.2008.03.009}, author = {Ratnasamy, Paul and Srinivas, Darbha} } @article { ISI:000311350000009, title = {Selective oxidation of cyclic olefins over framework Ti-substituted, three-dimensional, mesoporous Ti-SBA-12 and Ti-SBA-16 molecular sieves}, journal = {Catalysis Today}, volume = {198}, number = {1, SI}, year = {2012}, month = {DEC}, pages = {59-68}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Framework Ti-substituted, three-dimensional, mesoporous titanosilicates, Ti-SBA-12 and Ti-SBA-16, were prepared by direct hydrothermal synthesis method. These catalysts showed catalytic activity higher than the hitherto known titanosilicates for the oxidation of cyclic olefins (cyclohexene and cyclooctene) with tert.-butyl hydroperoxide. An epoxide selectivity of 100\% and olefin conversion greater than 92\% were obtained. Cubic Ti-SBA-16 with interconnected cage-like mesopore structure was more active than hexagonal Ti-SBA-12. X-ray diffraction and diffuse reflectance UV-vis, Fourier transform infrared, Raman and electron paramagnetic resonance spectroscopies provided evidence for the substitution of Ti4+ (for Si4+) in the framework locations. The catalytic activity correlated with the concentration of framework-substituted, tetrahedral Ti4+ ions. Easy accessibility of the active sites and the three-dimensional mesoporous structure are the possible causes for the superior activity of these titanosilicate catalysts. (C) 2012 Elsevier B. V. All rights reserved.

}, keywords = {Epoxidation of cyclic olefins, mesoporous materials, Molecular sieves, Selective oxidation, Ti-SBA-12, Ti-SBA-16, Titanosilicates}, issn = {0920-5861}, doi = {10.1016/j.cattod.2012.01.035}, author = {Kumar, Anuj and Srinivas, Darbha} } @article { ISI:000323361600008, title = {Three-dimensional, mesoporous titanosilicates as catalysts for producing biodiesel and biolubricants}, journal = {Journal of Molecular Catalysis A-Chemical}, volume = {377}, year = {2013}, month = {OCT}, pages = {65-73}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

The application of three-dimensional, mesoporous titanosilicates, Ti-SBA-12 and Ti-SBA-16, as reusable solid acid catalysts for producing biodiesel and biolubricants is reported for the first time. Biodiesel was prepared by esterification of oleic acid with monohydric methanol and biolubricants by esterification with polyhydric alcohols (glycerol, trimethylolpropane, neopentyl glycol and pentaerythritol). High catalytic activity of these catalysts is attributed to the presence of dispersed Lewis acidic Ti sites and mesoporosity in the structure. Biodiesel yields as high as 90 mol\% were obtained at 443 K. Surface hydrophobicity of the catalyst has also a predominant role, especially, in reactions involving polyhydric alcohols. In those reactions, Ti-SBA-16 showed higher catalytic activity than Ti-SBA-12. (c) 2013 Elsevier B.V. All rights reserved.

}, keywords = {Biodiesel, Esterification of fatty acid, Lubricant basestocks, mesoporous materials, Ti-SBA-12, Ti-SBA-16, Titanosilicates}, issn = {1381-1169}, doi = {10.1016/j.molcata.2013.04.029}, author = {Kotwal, Mehejabeen and Kumar, Anuj and Darbha, Srinivas} } @article {47634, title = {Role of metal-support interaction for atmospheric pressure CO2 hydrogenation over Pd/(Ti)-SBA-15 catalyst: effect of titanium composition on products selectivity}, journal = {Molecular Catalysis}, volume = {511}, year = {2021}, month = {JUL}, pages = {111732}, type = {Article}, abstract = {The potential role of metal-support interaction for tuning the product selectivity during atmospheric pressure CO2 hydrogenation has been demonstrated on Pd/(Ti)-SBA-15 catalyst. Highly dispersed Pd NPs on SBA-15 (Pd/ SBA-15) was synthesized and further modified with titanium of varying composition. Comparison of catalytic activity of Pd/Ti-SBA-15 with its counterparts (Pd/SBA-15 and Pd/TiO2) illustrated the significance of strong PdTi interface in this catalyst and its role in tuning the product selectivity of CO2 hydrogenation. The generation of an ample amount of oxygen vacancies in the Pd/Ti-SBA-15 catalyst with maximum metallic Pd sites in close vicinity of Ti is proposed to boost the CO2 hydrogenation activity.}, keywords = {CO2 hydrogenation, Metal-support interaction, Modified deposition precipitation, oxygen vacancies, Titanosilicates}, issn = {2468-8231}, doi = {10.1016/j.mcat.2021.111732}, author = {Soni, Yogita and Gupta, Sharad and Vinod, C. P.} }