Complex metal halide oxides (1): Bismuth chloride oxides having various structures as catalysts for oxidative coupling of methane

Article abstract of DOI:10.1246/bcsj.69.485

Bismuth chloride oxides having four distinct structural types and lanthanum-substituted bismuth chloride oxides were tested as catalysts for the oxidative coupling reaction of methane. Their catalytic properties were compared in relation with their structure. BiClO, which has a layer structure with a double chlorine sheet, so-called X₂ type structure, was most active for the methane conversion but less selective for the formation of C₂ hydrocarbons. The catalyst structure was quite unstable, so that the activity decreased markedly until reaching a constant level, while the selectivity increased. During these changes of the catalytic performance BiClO changed by liberating chlorine to Bi₂₄Cl₁₀O₃₁, the so-called Arppe's phase, and then finally to a highly stable and selective Bi₃ClO₄ phase which was constructed with a double metal oxygen sheet and a single chlorine sheet. When more chlorine was removed from Bi₃ClO₄, Bi₁₂Cl₂O₁₇, which has quintuple oxide sheets and a single chlorine sheet, was formed as an intermediate phase to be less selective for C₂ hydrocarbons and ultimately Bi₂O₃ was formed with no chlorine, to be nonselective. The substitution of Bi in Bi₃ClO₄ for La caused a decrease of the C₂ selectivity, whereas the Bi_3-xLa_xClO₄ catalysts treated with NaCl brought about a maximum yield of C₂ hydrocarbons.