Transient studies on the role of oxygen activation in the oxidative coupling of methane over Sm{sub 2}O{sub 3}, Sm{sub 2}O{sub 3}/MgO, and MgO catalytic surfaces

Journal Article · Tue Nov 01 04:00:00 EST 1994 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1994.1323· OSTI ID:28669

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

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1. Ruhr-Universitaet Bochum (Germany)

The interaction of oxygen with catalytic surfaces of MgO, Sm{sub 2}O{sub 3}, and Sm{sub 2}O{sub 3} (5 mol%)/MgO and the reaction of methane with short-lived surface oxygen species over Sm{sub 2}O{sub 3} were studied by transient experiments. The oxygen exchange between gas-phase {sup 18}O{sub 2} and surface oxygen {sup 16}O{sub s} was investigated in the temperature range from 539 to 1035 K. The oxygen-exchange activity decreased from Sm{sub 2}O{sub 3} (E{sub a} = 81 kJ/mol) via Sm{sub 2}O{sub 3}/MgO (E{sub a} = 96 kJ/mol) to MgO (E{sub a} = 261 kJ/mol). The presence of methane did not influence the exchange rate of {sup 18}O{sub 2} with the surface. This indicates (a) that oxygen activation on the surface is faster than activation of methane and (b) that neither gas-phase oxygen nor nondissociated surface oxygen is involved in the reaction with methane under the reaction conditions applied. It was shown that the surface reaction of methane with oxygen intermediates formed from gas-phase O{sub 2} is faster than the desorption of any diatomic oxygen species. Over Sm{sub 2}O{sub 3}, the degree of oxidative conversion of methane and the resulting product distribution are determined by the amount of surface-oxygen species formed by dissociation of gaseous O{sub 2} on the catalyst surface. It is suggested that these active oxygen sites consist of highly reactive short-lived species (below 200 ms) and also species having longer lifetimes. 16 refs., 11 figs., 2 tabs.

• OSTI ID: 28669
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 150; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

10 SYNTHETIC FUELS
40 CHEMISTRY
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
MAGNESIUM OXIDES
METHANE
OXIDATION
OXYGEN
REACTION INTERMEDIATES
SAMARIUM OXIDES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K