Synthesis and characterization of 1,2,3,4 tetrahydroquinoline intercalated into MoS 2 in search of cleaner fuels
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Felicia Manciu Department of Physics, University of Texas at El Paso, El Paso, Texas 79968
J.G. Parsons and Russell R. Chianelli Department of Chemistry, University of Texas at El Paso, El Paso, Texas 79968 (Received 26 January 2007; accepted 17 May 2007)
Two different morphologies of MoS2 (short and long sheets) were utilized to elucidate the intercalation mechanism of 1,2,3,4 tetrahydroquinoline (THQ). MoS2 (short sheets) and molybdenite (MB) (long sheets) were exfoliated and restacked in the presence of THQ. The x-ray diffraction patterns of both samples show a new reflection in the 001 plane, which implies a lowering of symmetry and corresponds to an expansion of the layers by approximately 12.3 Å. In the MoS2-THQ sample, 80% of the MoS2 was intercalated and 20% remained stacked. In the MB-THQ sample, 30% of MB was intercalated while 70% remained stacked. X-ray absorption structure (XAS) studies showed changes in atomic geometry and coordination. The x-ray absorption near-edge spectra showed shifts in the geometry of the intercalated MoS2 and MB sample compared to the unintercalated samples. Extended x-ray absorption fine structure studies showed lower coordination numbers compared to the untreated samples. Infrared spectroscopy characterization of these same samples suggests intercalation and partial dehydrogenation of the THQ.
I. INTRODUCTION
Hydrodesulfurization (HDS) processes use transition metal dichalcogenides, which are layered anisotropic compounds with Van der Waals interactions between the layers.1–3 MoS2 supported on Al2O3 and promoted with cobalt or nickel has been widely used as a hydrodesulfurization catalyst.4–11 However, the quality of crude oils in the United States has been decreasing due to a worldwide decreasing supply of light crude oils. Furthermore, the presence of highly hindered sulfurcontaining molecules in crude oils, such as substituted dibenzothiophenes, makes desulfurization more difficult under typical HDS reaction conditions.12 Thus, there is a need to improve hydrogenation catalytic activities to remove hindered sulfur-containing molecules from crude oils. In this paper, we report the interaction of a hydrogen donating molecule 1,2,3,4 tetrahydroquinoline (THQ) and a hydrogenation catalyst (MoS2). This interaction should shed some light on the hydrogenation activity of MoS2 with aromatic compounds (THQ). Furthermore, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0343 J. Mater. Res., Vol. 22, No. 10, Oct 2007
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the association of the THQ with MoS2 yields a new material for enhanced hydrogenation activity. It has been reported that in the presence of ReS2, dehydrogenation polymerization of THQ occurs.13,14 In the present study, the dehydrogenation activity of MoS2 was explored through the intercalation of THQ. This process is reversible under hydrogen pressure; thus we gain direct insight into the hydrogenation/dehydrogenation mechanism in synthesis of the intercalated co
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