The Effect of Chloride Ions on a Li+-MgO Catalyst for the Oxidative Coupling of Methane

• Published in: Journal of catalysis 1994-05, Vol.147 (1), p.301-310
• Main Authors: Lunsford, J.H., Hinson, P.G., Rosynek, M.P., Shi, C.L., Xu, M.T., Yang, X.M.
• Format: Article
• Language: English
• Subjects: 03 NATURAL GAS; 033000 - Natural Gas- Properties & Composition; 10 SYNTHETIC FUELS; 100200 - Synthetic Fuels- Production- (1990-); 400201 - Chemical & Physicochemical Properties; ALKALI METAL COMPOUNDS; ALKALINE EARTH METAL COMPOUNDS; ALKANES; ALKYL RADICALS; CATALYSIS; Catalysts: preparations and properties; CATALYTIC EFFECTS; CHALCOGENIDES; CHEMICAL REACTIONS; Chemistry; CHLORIDES; CHLORINE COMPOUNDS; Exact sciences and technology; General and physical chemistry; HALIDES; HALOGEN COMPOUNDS; HETEROGENEOUS CATALYSIS; HYDROCARBONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LITHIUM CHLORIDES; LITHIUM COMPOUNDS; LITHIUM HALIDES; LITHIUM OXIDES; MAGNESIUM CHLORIDES; MAGNESIUM COMPOUNDS; MAGNESIUM OXIDES; METHANE; METHYL RADICALS; ORGANIC COMPOUNDS; OXIDATION; OXIDES; OXYGEN COMPOUNDS; RADICALS; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1994.1141

At Cl/Li atomic ratios approaching unity, Li+-Mgo-Cl− catalysts undergo a marked change in behavior with respect to the oxidative coupling of CH4 to form C2H4 and C2H6 hydrocarbons. Most significant are the large C2H4/C2H6 ratios that may be obtained, primarily as a result of the enhanced activity for the oxidative dehydrogenation of C2H6. The presence Of Cl− ions at the appropriate level modifies the catalyst so that it no longer functions as a strongly basic oxide. In particular, the catalyst is not poisoned by CO2, which normally dominates the kinetic behavior of a Li+-MgO catalyst. The intrinsic activity for CH3 · radical generation over a properly chlorided Li+-MgO catalyst is less than that of a normal catalyst, but after poisoning by CO2, the activities of the two catalysts are comparable. At the typical reaction temperature of 650°C, chlorine is slowly lost from the catalyst, but this chlorine may be replaced by adding a small amount of HCl intermittently to the feed stream. At temperatures as low as 625°C, a CH4 conversion of 29% and a C2+ selectivity of 60% may be achieved.