Effect of Reactant Ratios on Methane Oxychlorination Over CeO₂ Catalyst

The oxidative chlorination of methane to produce chloromethane (CH₃Cl, CM) over CeO₂ catalyst was investigated as a function of various reactant ratios to obtain the optimum condition with the highest yield of the target product (CH₃Cl). The reactions were carried out at 480 °C by changing O₂ and HCl concentrations at fixed CH₄ concentration. It was found that the ratio of O₂:HCl (1:2) is the most important parameter to obtain high CH₄ conversion and CH₃Cl selectivity. Note that excessive HCl gives rise to the formation of the increased amount of more chlorinated products, such as CH₂Cl₂ or CHCl₃, due to the subsequent chain reaction with HCl and excessive O₂ promoting the oxidation of methane to CO and CO₂. The optimum reactant ratio of CH₄:O₂:HCl was 4:1.5:₃, with the highest CH₃Cl yield (14.3%). Various characterization results indicated that CeO₂ catalyst was slightly sintered, and had no carbon and chlorine deposition on the surface after the reaction.