THE EFFECT OF CHLORIDE-IONS ON A LI+-MGO CATALYST FOR THE OXIDATIVE COUPLING OF METHANE
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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 650C, 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 625C, a CH4 conversion of 29% and a C2+ selectivity of 60% may be achieved. 1994 Academic Press, Inc.
