Kinetics of methane oxidative coupling on Li-doped TiO[sub 2] catalysts

Journal Article · Mon Mar 01 04:00:00 EST 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1064· OSTI ID:7368859

Efstathiou, A M; Boudouvas, D; Vamvouka, N; Verykios, X E ^[1]

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1. Univ. of Patras (Greece)

A kinetic study of methane conversion to C[sub 2]-hydrocarbons was conducted by cofeeding methane and oxygen at 1 bar total pressure over a series of Li-doped TiO[sub 2] catalysts. The lithium dopant concentration was varied between 1 and 4 wt % Li[sub 2]O. Electrical conductivity measurements confirmed the incorporation of Li[sup +] into the crystal lattice of rutile TiO[sub 2], XPS measurements the enrichment of the surface with lithium, and XRD the presence of Li[sub 2]TiO[sub 3] in the 4 wt % Li[sub 2]O-doped TiO[sub 2] catalyst. It was found that the overall activation energy for methane conversion was independent of the Li[sup +] dopant concentration (E = 45 kcal mol[sup [minus]1]), a result opposite to that for C[sub 2]-hydrocarbons and CO[sub x] (x = 1, 2) formation. An optimum in methane activity was observed in the range between 0.5 and 1.5 wt % Li[sub 2]O dopant concentration. On the other hand, selectivity towards C[sub 2]-hydrocarbons showed a rather monotonic increase with Li[sup +] dopant concentration over a wide range of temperatures and partial pressures of methane and oxygen. The rates of C[sub 2]-hydrocarbons and CO[sub x] formation showed dependence on Li[sup +] dopant concentration and also on methane/oxygen ratio. CO[sub 2] chemisorption followed by temperature-programmed desorption was used as a probe technique to characterize the basicity of the series of Li-doped TiO[sub 2] catalysts. It was found that the 1 wt % Li[sub 2]O-doped TiO[sub 2] exhibited the highest amount of CO[sub 2] uptake. A distribution in the strength of basic sites was also observed. Surface acidity measurements by amine titrations over the series of Li-doped TiO[sub 2] catalysts revealed that total acidity decreases with increasing Li[sup +] dopant concentration. Surface basicity and acidity results seem to be related to the catalysis of the oxidative coupling of methane reaction over Li-doped TiO[sub 2] catalysts. 12 figs., 2 tabs.

• OSTI ID: 7368859
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 140:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

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ACTIVATION ENERGY
ALKALI METAL COMPOUNDS
ALKANES
CARBON COMPOUNDS
CARBON OXIDES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CATIONS
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
CONCENTRATION RATIO
COUPLING
DESORPTION
DIFFRACTION
DISTRIBUTION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY
ENRICHMENT
HETEROGENEOUS CATALYSIS
HYDROCARBONS
IONS
KINETICS
LITHIUM COMPOUNDS
MATERIALS
METHANE
MINERALS
NONMETALS
ORGANIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PHYSICAL PROPERTIES
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
REACTION KINETICS
RUTILE
SCATTERING
SEPARATION PROCESSES
SORPTION
SPECTROSCOPY
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
UPTAKE
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY