Complex Metal Halide Oxides (2). Layered Complex Metal Chloride Oxides Having the X1X2 Structure as Catalysts for the Oxidative Dehydrogenation of Ethane

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Abstract
SrBi3O4Cl3 with the X1X2 structure, in which metal–oxygen sheets were separated by single chlorine layers and double chlorine layers alternately, has been prepared and tested as a catalyst for the oxidative dehydrogenation of ethane. SrBi3O4Cl3 crystallized in space-group I4/mmm with lattice parameters of a = 3.9370(1), c = 27.0177(7) Å. The structure was refined by a Rietveld analysis, which showed that between two Bi(1) and Bi(2) sites, the former being of Bi in the metal–oxygen sheet faced the single chlorine sheet and the later faced the double chlorine sheet, strontium ions occupied the Bi(2) site only, and did not occupy the Bi(1) site. The SrBi3O4Cl3 catalyst showed a good catalytic performance for the oxidative dehydrogenation of ethane. Particularly, a high selectivity to ethene of more than 90% was obtained. Based upon an investigation of the potential role of chlorine during the cource of the reaction, it was apparently shown that a role of surface chlorine species was important, rather than gas-phase chlorine, for the reaction. It is considered that the high selectivity to ethene can be attributed to the fact that the chlorine radical mechanism operates on the catalysts, and that the surface chlorine blocks the formation of active-oxygen species to prevent destructive oxidation reactions.