LITHIUM CHEMISTRY OF LITHIUM DOPED MAGNESIUM-OXIDE CATALYSTS USED IN THE OXIDATIVE COUPLING OF METHANE

Active sites are created on the surface of a Li/MgO catalyst used for the selective oxidation of methane by the gradual loss of carbon dioxide from surface carbonate species in the presence of oxygen. Decomposition of the carbonate species in the absence of oxygen is detrimental to the activity of the catalyst. The active sites created are not stable but disappear either as a result of reaction with SiO2 to form Li2SiO3 or by the formation and subsequent loss of the volatile compound LiOH. In general the addition of water to the gas feed is detrimental to the stability of the catalyst. In the case of Li2CO3 strongly bonded on the surface of Li/MgO catalyst, the decomposition of the carbonate and thus the initial activity, can be enhanced by the addition of water to the gas feed. The addition of carbon dioxide to the gas feed results in a poisoning of the catalyst, the degree of this poisoning depending on the activity of the catalyst. The deactivation of the catalyst can be retarded if low concentration of carbon dioxide are added to the reaction mixture. It is possible to improve the stability of the catalyst by periodic reversal of the direction of flow of the gas steam. © 1990.