Transient studies on reaction steps in the oxidative coupling of methane over catalytic surfaces of MgO and Sm[sub 2]O[sub 3]

Journal Article · Fri Apr 01 04:00:00 EST 1994 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1994.1073· OSTI ID:7203845

Buyevskaya, O V ^[1]; Rothaemel, M; Zanthoff, H W; Baerns, M ^[2]

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1. Boreskov Institute of Catalysis, Novosibirsk (Russian Federation)
2. 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), Journal Name: Journal of Catalysis; (United States) Vol. 146:2; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030400* -- Natural Gas-- Products &amp; By-Products
10 SYNTHETIC FUELS
100200 -- Synthetic Fuels-- Production-- (1990-)
ALKALINE EARTH METAL COMPOUNDS
ALKANES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
DEUTERIUM COMPOUNDS
HETEROGENEOUS CATALYSIS
HYDROCARBONS
HYDROGEN COMPOUNDS
ISOTOPIC EXCHANGE
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
METHANE
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
RADICALS
RARE EARTH COMPOUNDS
SAMARIUM COMPOUNDS
SAMARIUM OXIDES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K