Transient studies on reaction steps in the oxidative coupling of methane over catalytic surfaces of MgO and Sm[sub 2]O[sub 3]
- Boreskov Institute of Catalysis, Novosibirsk (Russian Federation)
- Ruhr-Universitaet Bochum (Germany)
Adsorption of CH[sub 4] and O[sub 2] as well as surface reactions of CH[sub 4], CD[sub 4], and CH[sub 4]-CD[sub 4] mixtures in the absence and presence of gas phase oxygen were studied over MgO and Sm[sub 2]O[sub 3] in the temperature range from 373 to 1073 K applying the temporal analysis of products (TAP) reactor. Formation of CH[sub 3][center dot] radicals was observed during surface reaction of methane in the Knudsen-diffusion regime while ethane and ethylene were detected only at increasing pulse intensity, i.e., in the molecular-diffusion regime. The reactivity of surface-lattice oxygen of MgO and Sm[sub 2]O[sub 3] was studied in the Knudsen regime with respect to the H-D exchange in methane. Surface hydroxyl groups were found to participate in this reaction, but no direct interaction of methane molecules on the catalyst surface occurred. H-D exchange proceeds via a multistep mechanism involving methane-surface interaction leading to dissociative adsorption of methane. On MgO, surface-lattice oxygen is responsible for methyl radical formation resulting in C[sub 2] hydrocarbons, while adsorbed oxygen species have very short lifetimes (<0.1 s) on the surface and take part in the reactions of total oxidation. On Sm[sub 2]O[sub 3], active oxygen species formed by the interaction of gaseous O[sub 2] with the catalyst surface have lifetimes up to 20 s and are mainly responsible for methane conversion and product formation. Based on the response analysis it was assumed that direct interaction of gas-phase methane with active oxygen surface species is the first step in the oxidative coupling of methane (OCM) over Sm[sub 2]O[sub 3]. It was found that the type of methane activation which takes place in H-D exchange was not involved in the OCM reaction over Sm[sub 2]O[sub 3]. 38 refs., 10 figs., 3 tabs.
- OSTI ID:
- 7203845
- Journal Information:
- Journal of Catalysis; (United States), Vol. 146:2; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
10 SYNTHETIC FUELS
MAGNESIUM OXIDES
CATALYTIC EFFECTS
METHANE
OXIDATION
SAMARIUM OXIDES
CATALYSTS
DEUTERIUM COMPOUNDS
HETEROGENEOUS CATALYSIS
ISOTOPIC EXCHANGE
RADICALS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
ALKALINE EARTH METAL COMPOUNDS
ALKANES
CATALYSIS
CHALCOGENIDES
CHEMICAL REACTIONS
HYDROCARBONS
HYDROGEN COMPOUNDS
MAGNESIUM COMPOUNDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
SAMARIUM COMPOUNDS
TEMPERATURE RANGE
030400* - Natural Gas- Products & By-Products
100200 - Synthetic Fuels- Production- (1990-)