CATALYTIC PARTIAL OXIDATION OF METHANE OVER BA-PB, BA-BI, AND BA-SN PEROVSKITES
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Catalytic behaviors of the stoichiometric perovskites BaPbO 3 , BaBiO 3 , and BaSnO 3 , and ofcorresponding materials containing excess Ba, have been investigated for the oxidative coupling of methane. The Ba-Pb and Ba-Bi perovskites are more active and produce substantially higher C 2 product yields (12-15%) at 800 C than does the Ba-Sn material (4%). XRD analyses of the used catalysts indicate that BaPbO 3 and BaBiO 3 undergo extensive bulk decomposition under CH 4 /O 2 reaction conditions, forming BaCO 3 and BaO 2 phases, together with either PbO x , or Bi 2 O 3 . XPS characterization reveals that the surfaces of both materials become enriched in Ba as a result of their bulk decompositions. BaSnO 3 , by contrast, does not undergo significant changes in either its bulk or surface compositions as a result of the oxidation reaction. A significant portion of the surfaceBa on these materials during reaction exists as BaCO 3 , which is generated from the CO 2 reaction product and which is partially converted into the active BaO 2 phaseby reaction with O 2 . 1993 Academic Press, Inc.