Catalytic combustion of dichloromethane over NaFAU and HFAU zeolites: a combined experimental and theoretical study

The catalytic combustion of dichloromethane (DCM) was examined over NaFAU and HFAU zeolites by experimental and theoretical studies. The reactions yielded carbon monoxide, hydrogen chloride, water, and methyl chloride as major products. The order of reaction was one with respect to DCM concentration, and the activation energy and pre-exponential factors were determined. Insight into the mechanism of catalytic combustion of DCM was gained by the B3LYP/6-31G(d, p) method using the 15T (T = Si or Al tetrahedral) cluster model of FAU zeolite. The results revealed that the combustion of DCM was catalyzed by FAU zeolite via the stepwise mechanism involving adsorption, dechlorination, hydrolysis, and oxidation steps in humid air. NaFAU was found to be more active than HFAU because it facilitated the adsorption and dechlorination steps, which was in agreement with the experimental result. The transformation between NaFAU and HFAU requires low activation energy (∆E = 19.2 kJ mol−1). The calculated activation barriers for the dechlorination and hydrolysis steps over NaFAU and HFAU were 82.1 and 124.2 kJ mol−1, respectively. Dechlorination of DCM was predicted to be the rate-determining step. The calculated apparent activation barrier for the combustion of DCM over NaFAU was 86.0 kJ mol−1, which was consistent with the experimental value of 84.8 kJ mol−1.