OXIDATIVE COUPLING OF METHANE OVER OXIDE-SUPPORTED BARIUM CATALYSTS
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The effects of barium loading level and support basicity on the activity and C 2+ selectivity for oxidative coupling of methane were examined for MgO-, CaO-, ZnO-, and Al 2 O 3 -supported Ba catalysts. The nature and distribution of catalyst surface species were characterized by XPS and ISS spectroscopic techniques, which indicated that there is no direct correlation between support basicity and oxidative coupling activity. However, catalysts containing sufficiently high Ba loadings are more easily poisoned by carbon dioxide than those with low Ba contents, due to increased stability of a BaCO 3 phase. With supports of low basicity, or when the Ba is uniformly distributed on the catalyst support, the susceptibility to carbon dioxide poisoning is minimized. XPS characterization of the Ba/MgO catalysts confirmed that oxidative coupling activity is directly related to the capability of the catalyst to form surface O 2-2 ions existing in a BaO 2 phase that is sustained under reaction conditions by the presence of molecular O 2 . With a 2 mol% Ba/MgO catalyst, a C 2+ selectivity of 80% at a CH 4 conversion of 17% was achieved using a CH 4 : O 2 = 10: 1 reactant mixture at 800C and a total reagent pressure of 1 atm. 1993 Academic Press, Inc.
