NO₂-catalyzed deep oxidation of methanol: Experimental and theoretical studies

The NO₂-catalyzed deep oxidation of methanol has been studied by both experimental and theoretical techniques. On-line infrared (IR) and in situ IR investigations show that a trace amount of NO_x (for example, 600 ppm NO and/or NO₂) can dramatically promote the oxidation of methanol as manifested by the reduced reaction temperature together with significantly enhanced CO₂ selectivity. The reactions of methanol and nitrogen dioxide are investigated by theoretical calculations at the CBS-Q//B3LYP/6-311++G(2d,p) level of theory. Seven channels are found totally. The calculated reaction barriers of the controlling steps of the two lowest channels are 20.5 and 21.1 kcal mol^-1, which are in good agreement with the reported experimental value of 21.4 kcal mol^-1. The reaction rate constants are also calculated by the microcanonical variational transition state theory (μVT) with tunneling corrections. The three-parameter fitting expression for the overall forward rate constant is 1.72 × 10^-22T^3.38 exp (-10153 T^-1) cm³ molecule^-1 s^-1. The theoretical simulation of methanol conversion is in satisfactory agreement with the experiment. A reaction mechanism for the CH₃OH{single bond}O₂{single bond}NO_x system has been proposed based on the experimental and theoretical studies.