Structural and kinetic study of CoMo/. gamma. Al/sub 2/O/sub 3/ hydrodesulfurization catalyst using EXAFS and XANES

Thesis/Dissertation · Sat Jan 01 00:00:00 EST 1983

OSTI ID:6651376

Parham, T G

In situ Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge (XANES) spectroscopies were combined in a study designed to elucidate the molecular structure of molybdenum in CoMo/..gamma..Al/sub 2/O/sub 3/ hydrodesulfurization catalysts. This structure was related to catalytic activity using a model thiophene hydrodesulfurization reaction. Oxide CoMo/..gamma..Al/sub 2/O/sub 3/ was found to consist of tetrahedrally coordinated molybdenum with two or three short Mo = O bonds and one or two oxide ligands with longer Mo-O distances. The catalyst reacts with H/sub 2/S at 25 C with terminal Mo = O species being replaced by sulfur ligands. As the sulfiding temperature is increased, oxysulfides are replaced with a MoS/sub 2/-like phase. No evidence was found of oxysulfides at sulfiding temperatures in excess of 200 C. The first shell sulfur and second shell molybdenum coordination numbers were observed to increase linearly with sulfiding temperature, as was the present MoS/sub 2/-like phase. The MoS/sub 2/-like phase is remarkably similar to MoS/sub 2/, but has a Mo-S coordination number of only four. The second shell coordination is also lower, with only three molybdenum neighbors at 3.16 A. Sulfiding is about 90% complete after two hours at 400 C, with only minor change after 24 hours of sulfiding. This information is consistent with a structural model consisting of small MoS/sub 2/ crystallites of c.a. 10 A if the perimeter molybdenums are considered to have lost labile sulfur. Kinetic EXAFS, XANES and sulfur uptake measurements were made in situ during catalyst sulfiding and HDS. These measurements showed that at high temperature (400 C) the rate of sulfur adsorption onto the catalyst limits the rate of reaction between surface sulfur and molybdenum.

• OSTI ID: 6651376
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
10 SYNTHETIC FUELS
ALUMINIUM OXIDES
CATALYTIC EFFECTS
COBALT
DESULFURIZATION
CATALYSTS
HYDROCARBONS
MOLYBDENUM
REMOVAL
SULFUR
X-RAY SPECTROSCOPY
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
METALS
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
SPECTROSCOPY
TRANSITION ELEMENTS
020400* - Petroleum- Processing
090100 - Hydrocarbon Fuels- (-1989)