The combustion of lean mixtures of chloromethane in thermally and catalytically stabilised thermal reactors is considered in this paper. A plug flow model is adopted, with detailed kinetics for homogeneous combustion; mass transfer limitations to the reactive wall are considered, and the influence of gas phase reactions on mass transport coefficients is taken into consideration. The numerical investigation evidenced that the final product distribution is very sensitive to the scheme of heterogeneous reactions considered. By means of a sensitivity analysis, a reduced lumped mechanism is proposed for the reactions at the catalytic wall which is able to describe the experimental data.