Experimental Verification of Theoretically Calculated Transition Barriers of the Reactions in a Gaseous Selective Oxidation of CH₄−O₂−NO₂

The selective oxidation of methane with oxygen to C 1 oxygenates (methanol and formaldehyde) is an important process. However, the precise reaction mechanism in a gaseous chain reaction has not been clarified. Methane activation and the selectivity of C 1 oxygenates (CH 3 OH, CH 2 O) in a gaseous selective oxidation of CH 4 −O 2 −NO 2 have been examined under atmospheric pressure with both theoretical and experimental approaches. Theoretically calculated transition barrier of hydrogen abstraction from CH 4 of the reaction CH 4 + NO 2 → CH 3 + HNO 2 was lower than that of the reaction with O 2, i.e., CH 4 + O 2 → CH 3 + O 2 H. This decrease of the transition barrier was experimentally verified by the linear enhancement of CH 4 conversion with NO 2 concentration in CH 4 −O 2 −NO 2 . The experimental varied results of selectivity of C 1 oxygenates on various reaction conditions (NO 2 concentration, CH 4 /O 2 ratio, space velocity) showed the appropriateness of the consideration on the selectivity with the calculated values of transition barriers and rate constants of the selected reaction routes from CH 3 O to CH 3 OH and CH 2 O. After considering the transition barriers and rate constants of each elemental reaction route, we attained ca. 7% yield of C 1 oxygenates.