Several chloride catalysts, both unsupported and supported, have been prepared and investigated as catalysts for the oxidative coupling of methane. The results show that the chlorides of the alkaline earth metals are selective for the formation of ethane, especially when supported on an oxide, but are not very selective for the formation of ethene. In the case of MnCl2 it has been found that the pure chloride has a very low selectivity for the formation of any C2 products. Partial oxidation of the MnCl2 results in a catalyst with a high selectivity to C2 products, especially ethene, but this material is very unstable. High ethene-to-ethane ratios are observed initially, but in the approach to a steady state this ratio decreases to less than 1:1. Addition of an alkali chloride to MnCl2 improves the selectivity and stability of the catalyst. The influence of gas phase reactions on the ethene-to-ethane ratio is discussed. It is concluded that the initial high ethene-to-ethane ratio is mainly attributable to gas phase reactions involving chlorine radicals, but that under steady-state conditions a manganese oxychloride surface is capable of converting methane into both ethene and ethane with high selectivity. © 1989.
