Catalytic Partial Oxidation of Methane over Ba-Pb, Ba-Bi, and Ba-Sn Perovskites

Catalytic behaviors of the stoichiometric perovskites BaPbO 3, BaBiO 3, and BaSnO 3, and of corresponding 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 2O 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 surface Ba 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 phase by reaction with O 2.