Mechanism of catalytic oxidation of CH_2Cl_2 on gamma -Al_2O_3 and aluminosilicates

摘要

Oxidation of CH_2Cl_2 with dioxygen has been investigated on pure gamma -Al_2O_3 and Al_2O_3-SiO_2 system in the whole composition range.Two mechanisms of the reaction operate.At temperatures below 400 deg C CH_3Cl is formed as intermediate,with simultaneous evolution of CH_2Cl_2 through a chlorine apex at a Lewis site,the adsorbed species transforming by S_N2 reaction to chlorometoxy- and methoxy-species and then by Cannizzaro-type reaction to a formate precursor and finally CO, ahydrogen transfer to chloromethoxy-species giving CH_3Cl.Results of in situ IR spectroscopic studies are in line with such model.At higher temperatures 100