Bimetallic synergy in cobalt-ruthenium Fischer-Tropsch synthesis catalysts
- Exxon Research and Engineering Co., Annandale, NJ (United States)
The addition of small amounts of Ru to Co/TiO[sub 2] or Co/SiO[sub 2] catalysts (Ru/Co < 0.008 at.) increases their turnover rate and C[sub 5]+ selectivity in the Fischer-Tropsch synthesis. Also, deactivated bimetallic Co-Ru catalysts can be regenerated by a hydrogen treatment at reaction temperatures whereas monometallic Co catalysts cannot. On Co/TiO[sub 2], Ru addition increases turnover rates by a factor of three and C[sub 5]+ selectivities from 84.5 to 91.1%, without an apparent change in cobalt dispersion. Activation energies and reaction kinetics are unaffected by Ru addition. These data suggest that the presence of Ru leads to higher Co site density during reaction without modifying the chemical reactivity of exposed Co surface atoms. Ru appears to inhibit the deactivation of surface Co ensembles. Ru atoms at the surface of Co crystallites increase the rate of removal of carbon and oxygen species during reaction and during regeneration of deactivated Co catalysts. The resulting higher Co site density leads to higher apparent turnover rates and to enhanced readsorption of [alpha]-olefins. As a result, Co-Ru catalysts yield a heavier and more paraffinic product than monometallic Co catalysts with similar initial dispersion. The observed bimetallic interactions require intimate contact between Co and Ru, a state that forms during oxidation of the bimetallic precursors at high temperature. This treatment induces migration of Ru oxide species and leads to mixed Co-Ru oxides. The reducibility and the carbon deposition rates on well-mixed bimetallic Co-Ru catalysts are very different from those of monometallic Co catalysts. Electron microscopy, X-ray absorption spectroscopy, and thermogravimetric studies confirm the intimate mixing required for catalytic rate and C[sub 5]+ selectivity enhancements, for faster reduction of Co oxide precursor, and for inhibition of carbon deposits during reactions of H[sub 2]/CO mixtures. 40 refs., 14 figs., 7 tabs.
- OSTI ID:
- 5154898
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 143:2; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
100200 -- Synthetic Fuels-- Production-- (1990-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKENES
CATALYST SUPPORTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
COBALT COMPLEXES
COMPLEXES
GRAVIMETRIC ANALYSIS
HYDROCARBONS
KINETICS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
QUANTITATIVE CHEMICAL ANALYSIS
REACTION KINETICS
RUTHENIUM COMPLEXES
SPECTROSCOPY
SYNTHESIS
THERMAL ANALYSIS
THERMAL GRAVIMETRIC ANALYSIS
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
X-RAY SPECTROSCOPY
YIELDS