Surface phenomena during the oxidative coupling of methane over Li/MgO

• Published in: Journal of catalysis 1991-09, Vol.131 (1), p.143-155
• Main Authors: Peil, Kevin P., Goodwin, James G., Marcelin, George
• Format: Article
• Language: English
• Subjects: 03 NATURAL GAS; 030300 - Natural Gas- Drilling, Production, & Processing; 10 SYNTHETIC FUELS; 100200 - Synthetic Fuels- Production- (1990-); ALKALI METALS; ALKALINE EARTH METAL COMPOUNDS; ALKANES; ALKENES; CARBON COMPOUNDS; CARBON DIOXIDE; CARBON MONOXIDE; CARBON OXIDES; Catalysis; CATALYTIC EFFECTS; CATALYTIC REFORMING; CHALCOGENIDES; CHEMICAL REACTION KINETICS; CHEMICAL REACTIONS; Chemistry; ELEMENTS; ETHANE; ETHYLENE; Exact sciences and technology; General and physical chemistry; HYDROCARBONS; KINETICS; LITHIUM; MAGNESIUM COMPOUNDS; MAGNESIUM OXIDES; METALS; METHANE; NONMETALS; ORGANIC COMPOUNDS; OXIDATION; OXIDES; OXYGEN; OXYGEN COMPOUNDS; REACTION INTERMEDIATES; REACTION KINETICS; REFORMER PROCESSES; SURFACE PROPERTIES; SYNTHESIS; TEMPERATURE RANGE; TEMPERATURE RANGE 0273-0400 K; TEMPERATURE RANGE 0400-1000 K; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(91)90331-W

This paper details an investigation of the oxidative coupling of methane for reaction temperatures up to 645°C over MgO and Li/MgO catalysts using steady-state isotopic transient kinetic analysis (SSITKA). Oxygen-exchange experiments in the absence of methane resulted in a quantification of the lattice oxygen diffusivity and total oxygen uptake. The catalyst had three more-or-less distinct regions: (1) the physical surface at which exchange between the gas phase and the solid occurred, (2) several subsurface atomic layers readily available for exchange, and (3) the bulk oxide. Using isotopic switches of oxygen and methane under steady-state reaction, the active intermediates along the carbon and oxygen reaction pathways were quantified. Lattice oxygen was found to play a significant role in the oxidation process under steady-state reaction. CO and CO 2 appeared to be formed via a multistep surface oxidation pathway while ethane was formed via surface-generated intermediates along a parallel pathway. Sites involved with the generation of intermediates for selective coupling were found to have a lower activity than sites active for the generation of nonselective intermediates.