An Investigation on the Role of NO2in the Oxidation of Methane to Formaldehyde

Experimental results and a kinetic modeling were previously reported for the gas phase oxidation of methane in the presence of NO2 at short residence time (20–80 ms) in a microreactor. A detailed kinetic analysis is carried out in the present study in means of flow rate and sensitivity analysis, in order to investigate the role of NO2. A comparison is made of the reaction systems with and without NO2. The concentration profiles of several key species are presented and analyzed in the present study. The CH3O· radicals are present in far larger quantities in the CH4/O2/NO2 system than in the CH4/O2 system. With NO2, the dominant route to HCHO is through CH3O·, primarily involving the reaction: CH3· + NO2 ⇔ CH3O· + NO, followed by: CH3O· (+M) ⇔ CH2O + H· (+M) and CH3O· + O2 ⇔ HO2· + CH2O. The promoting effects of NO2 can be explained by the interconversion NO2/NO, which is mainly related to: HO2· + NO ⇔ NO2 + OH·, NO2 + H· ⇔ NO + OH·, NO + CH3O2· ⇔ CH3O· + NO2 and NO2 + CH3· ⇔ CH3O· + NO.