Phase-Boundary Photocatalytic Oxidation of Dibenzothiophene Over Amphiphilic Ti-MCM-41 Molecular Sieve
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Phase-Boundary Photocatalytic Oxidation of Dibenzothiophene Over Amphiphilic Ti-MCM-41 Molecular Sieve Juan Zhang • Dishun Zhao • Zhen Ma Yanan Wang
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Received: 9 April 2010 / Accepted: 15 May 2010 / Published online: 8 June 2010 Ó Springer Science+Business Media, LLC 2010
Abstract Hydrophilic Ti-MCM-41 was modified by alkylsilyl groups using n-octadecyltrichlorosilane as the precursor, yielding an amphiphilic molecular sieve denoted as OTS-Ti-MCM-41. The sample retained mesoporous structure and morphology, as confirmed by XRD, N2 adsorption–desorption, and SEM. The presence of surface alkylsilyl groups was confirmed by infrared spectroscopy. The amphiphilic OTS-Ti-MCM-41 located at the boundary between aqueous and organic phases acted as a phaseboundary catalyst for the photooxidation of dibenzothiophene (DBT) without the need of adding a co-solvent to drive liquid–liquid phase transfer. With H2O2 as the oxidant, the conversion of DBT on OTS-Ti-MCM-41 was up to 98% at 2 h, much higher than that on Ti-MCM-41. When air was used instead of H2O2 as the oxidant, the conversion of DBT on OTS-Ti-MCM-41 was up to 85% at 2 h. Keywords Phase-boundary catalysis Amphiphilic Ti-MCM-41 Dibenzothiophene Photooxidation J. Zhang D. Zhao (&) College of Chemistry and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China e-mail: [email protected] J. Zhang e-mail: [email protected] Z. Ma Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China Y. Wang School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
1 Introduction Sulfur in fuels is a major source of atmospheric pollution because the combustion of fuels may lead to the production of sulfur oxides, precursors of acid rain. The sulfur level in diesel fuels is presently restricted to be 15 ppm in Japan, Europe, and the United States [1]. Oxidative desulfurization (ODS) is one of the most promising methods for deep desulfurization of fuel oil, because it can be carried out at room temperature and under atmospheric pressure [2–9]. In particular, photocatalytic oxidative desulfurization utilizes photo energy, and hence is particularly promising [10]. Matsuzawa et al. reported that dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in acetonitrile were photooxidized to 5-oxide (sulfoxide) and 5,5-dioxide (sulfone) of each substrate using TiO2 as the photocatalyst [11]. However, the conversions of DBT and 4,6-DMDBT were less than 40% after irradiation for 10 h. Titanium silicalite molecular sieves are able to catalyze a series of selective oxidation reactions such as aromatic hydroxylation, alkane oxidation, and alkene epoxidation [12–14]. Recently, a few studies were performed for the catalytic oxidation of organic sulfur compounds over Ti-containing molecular sieves under mild conditions [15–21]. For example, Reddy et al. [15] found that titanium silicate molecular sieves with MEL (TS-2) or MFI (TS-1) topology could efficiently catalyz
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