THE EFFECT OF CHLORIDE-IONS ON A LI+-MGO CATALYST FOR THE OXIDATIVE COUPLING OF METHANE

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-degrees-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-degrees-C, a CH4 conversion of 29% and a C2+ selectivity of 60% may be achieved. (C) 1994 Academic Press, Inc.