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Date of Award
Master of Science (MS)
Bussell, Mark E.
Patrick, David L.
Global demand for transportation fuels continues to rise while environmental standards for sulfur impurities in fuels have become more stringent. Upgrading crude oil feed stocks via deep hydrodesulfurization (HDS) is necessary to meet the ultra-low sulfur standards for transportation fuels. Transition metal phosphides (e.g. Ni2P, Ru2P) represents a new class of hydrotreating catalysts that show promise for improved HDS properties relative to conventional molybdenum sulfide based catalysts. Incorporating a second metal into Ni2P can influence the surface properties and be used to tailor the catalytic properties (activity, selectivity) for improved hydrotreating performance. Bimetallic phosphides catalysts having the formulas NixM2-xP/SiO2 (M = Ru, Rh) were synthesized over a range of compositions. Metal hypophosphite precursors prepared via incipient wetness were reduced via temperature programmed reduction (TPR). The resulting catalysts were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and CO chemisorption. HDS properties were probed using 4,6-dimethyldibenzothiophene (4,6-DMDBT) as a model compound. The XRD patterns showed single phase and phase-segregated materials having average crystallize sizes of 5-10 nm. CO chemisorption measurements showed an increase in active site density for the higher nickel content catalysts (e.g. Ni1.85Ru0.15P/SiO2). HDS measurements were carried out using a model feed of 1000 ppm 4,6-DMDBT in decalin over a range of temperatures (533-653 K). A substantial increase in the TOFs and HDS activity was observed for the bimetallic phosphides having high nickel contents. For the NixRh2-xP/SiO2 series, the product selectivity was observed to change with metal composition; for Rh-rich phases (x < 0.25), the hydrogenation product (3,3’-dimethylbicyclohexane) was favored while for Ni-rich compositions (x > 0.25) the partially hydrogenated product (3,3’-dimethylcyclohexylbenzene) dominated.
Western Washington University
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Topalian, Peter J., "Probing the catalytic properties of Ni-based bimetallic phosphides for deep hydrodesulfurization" (2017). WWU Graduate School Collection. 575.
Available for download on Saturday, May 18, 2019