| The general features of the oxidative coupling of methane have many similarities to selective oxidation of propylene. The Bi-P oxide system, which is one of the more active and selective catalysts for the oxidative dimerization of propylene, has been investigated for the oxidative coupling of methane. In this study, the supports, MgO, Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, SiO{dollar}sb2{dollar} and TiO{dollar}sb2{dollar}, were studied. It was found that MgO is the best support, followed by Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, SiO{dollar}sb2{dollar} and TiO{dollar}sb2{dollar}. The alkali promoters, Li, Na, K, and Cs, are good promoters for this catalyst system. By varying the amounts of Bi, P, and K, it was found that the optimum catalyst composition, in weight percent, is Bi{dollar}sb2{dollar}O{dollar}sb3{dollar}-5%, P{dollar}sb2{dollar}O{dollar}sb5{dollar}-10% and K{dollar}sb2{dollar}O-2.5%.; An isotopic tracer study on Bi-P-K-O/MgO (5%-10%-2.5%) catalyst indicated that the only isotope effect was for the formation of ethane and no isotope effect was found for converting methane to ethylene or for converting methane to carbon dioxide. The analyses of the isotopic distribution of the products indicated that only a small amounts of CH{dollar}sb3{dollar}D ({dollar}<{dollar}1%), and d{dollar}sb0{dollar}, d{dollar}sb1{dollar}, d{dollar}sb2{dollar}, d{dollar}sb3{dollar}, d{dollar}sb4{dollar}, d{dollar}sb5{dollar}-ethane ({dollar}<{dollar}1%) were produced as products of the CD{dollar}sb4{dollar}-O{dollar}sb2{dollar} reaction, but large amounts of d{dollar}sb0{dollar}- and d{dollar}sb1{dollar}, were found in the ethylene products.; The reaction order of methane was one for ethane and was one approximately one for ethylene. The reaction order of O{dollar}sb2{dollar} is complicated and varies with temperature. The activation energies are 23 (high temperature) and 56 (low temperature), 43 and 14 kcal/mole for ethane, ethylene and carbon dioxide, respectively. The selectivities for ethane, ethylene and carbon dioxide, at the zero contact time, are not zero. As the contact time increases, the selectivity decreases for ethane, increases for ethylene, and is constant for carbon dioxide. These experimental results can be explained by a mechanism that has ethane as a primary product, and ethylene as both a primary product and a secondary product. |
