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Titanium-substituted mesoporous SBA-15 molecular sieve has been successfully prepared at 373 K by direct synthesis under microwave-hydrothermal conditions within about 2 h. By means of X-ray diffraction, nitrogen adsorption, infrared, UV-vis diffuse reflectance, and Raman spectroscopies, a successful isomorphous substitution of titanium in the silica framework of SBA-15 samples with Si/Ti ratios of 20, 30, and 40 has been reported. The substitution of Ti for Si did not change the textural properties. The higher titanium loading leads to the formation of extraframework titanium species. These results show that microwave-assisted synthesis is an ideal approach to prepare Ti-substituted SBA-15, which is expected to be useful as a selective oxidation catalyst for reactions involving large molecules.

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Equilibrium adsorption isotherms for methane, ethane, ethylene, acetylene, propane, and propylene have been measured for the first time on mesoporous silica, SBA-15, and the data are analyzed by using the Langmuir-Freundlich adsorption isotherm model. The adsorption capacities for ethylene and propylene are found to be higher than those for corresponding alkanes. Likewise, adsorption of acetylene is more pronounced as compared to ethylene. The isosteric heats of adsorption for various adsorbates estimated by the Clausius-Clapeyron equation are higher for olefins and acetylene and are comparable with those reported for π-complexation based systems. Such a trend has in turn suggested a higher affinity of SBA-15 framework for alkenes over corresponding alkanes, which has been examined in terms of the textural characteristics of SBA-15. It is suggested that SBA-15 can potentially be a good adsorbent for separation of light hydrocarbons.