Masunov Artëm E, Wait Elizabeth, Vasu Subith S
South Ural State University , Lenin pr. 76, Chelyabinsk 454080, Russia.
National Research Nuclear University MEPhI , Kashirskoye shosse 31, Moscow 115409, Russia.
J Phys Chem A. 2017 Aug 3;121(30):5681-5689. doi: 10.1021/acs.jpca.7b04897. Epub 2017 Jul 19.
The supercritical carbon dioxide diluent is used to control the temperature and to increase the efficiency in oxycombustion fossil fuel energy technology. It may affect the rates of combustion by altering mechanisms of chemical reactions, compared to the ones at low CO concentrations. Here, we investigate potential energy surfaces of the four elementary reactions in the CH + O reactive system in the presence of one CO molecule. In the case of reaction CH + O → CHO + OH (R1 channel), van der Waals (vdW) complex formation stabilizes the transition state and reduces the activation barrier by ∼2.2 kcal/mol. Alternatively, covalently bonded CO may form a six-membered ring transition state and reduce the activation barrier by ∼0.6 kcal/mol. In case of reaction CH + O → CHO + O (R2 channel), covalent participation of CO lowers the barrier for the rate limiting step by 3.9 kcal/mol. This is expected to accelerate the R2 process, important for the branching step of the radical chain reaction mechanism. For the reaction CH + O → CHO + HO (R3 channel) with covalent participation of CO, the activation barrier is lowered by 0.5 kcal/mol. The reaction CHO + OH → CHO + HO (R4 channel) involves hydrogen abstraction from formaldehyde by OH radical. Its barrier is reduced from 7.1 to 0.8 kcal/mol by formation of vdW complex with spectator CO. These new findings are expected to improve the kinetic reaction mechanism describing combustion processes in supercritical CO medium.
