Kinetic mechanisms of hydrogen abstraction reactions from methanol by methyl, triplet methylene and formyl radicals

• Published in: Computational and theoretical chemistry Vol. 1074; pp. 73 - 82
• Main Authors: Shi, Jun, Ran, Jing-yu, Qin, Chang-lei, Qi, Wen-jie, Zhang, Li
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.12.2015
• Subjects: Formyl radical; H-abstraction; Kinetic mechanism; Methanol; Methyl radical; Triplet methylene radical; Methyl radical; Kinetic mechanism; Formyl radical; H-abstraction; Triplet methylene radical; Methanol
• ISSN: 2210-271X
• DOI: 10.1016/j.comptc.2015.10.009

[Display omitted] •Transition state and energy barrier of H-abstraction of methanol with methyl radical are obtained accurately.•Energy barrier calculated by MP2 is more accurate than that predicted by B3LYP density functional.•H-abstraction of methanol with triplet methylene and formyl radicals was studied firstly by theoretical method. Although H-abstraction reactions from methanol by methyl radical (CH3), triplet methylene radical (3CH2) and formyl radical (HCO) are important for methanol pyrolysis and combustion, the kinetic mechanisms of those reactions are indistinct and need to be better understood. Ab initio calculations were performed to optimize geometries of transition states using Gaussian 09W package with the B3LYP density functional at the 6-311++G (3df, 3pd) basis set. Energy barrier and minimum energy path (MEP) on the reaction potential energy surface were calculated with MP2 method at the same basis set. The canonical variational transition state theory (CVT) with Eckart tunneling correction were employed to compute rate constants over the temperature range 298–2000K. Results show that, for reaction CH3OH+CH3, barrier height for hydroxymethyl channel (R1a) is 12.59kcal/mol and for methoxyl channel (R1b) is 13.82kcal/mol. Rate constants for channels R1a and R1b are k1a=3.635×10−31T5.58exp(−1962/T)cm3molecule−1s−1, k1b=4.342×10−28T4.61exp(−4284/T)cm3molecule−1s−1, respectively. For reaction CH3OH+3CH2, barrier heights for hydroxymethyl channel (R2a) and methoxyl channel (R2b) are 7.68kcal/mol and 9.19kcal/mol, respectively. Rate constant for channel R2a is k2a=5.885×10−28T4.19exp(−1813/T)cm3molecule−1s−1 and for channel R2b is k2b=2.266×10−28T4.26exp(−2833/T)cm3molecule−1s−1. For reaction CH3OH+HCO, barrier heights for hydroxymethyl channel (R3a) and methoxyl channel (R3b) are 21.88kcal/mol and 28.83kcal/mol, respectively. Rate constant for channel R3a is k3a=8.156×10−38T7.37exp(−4900/T)cm3molecule−1s−1 and for channel R3b is k3b=2.007×10−27T4.34exp(−11,605/T)cm3molecule−1s−1. This study is beneficial for improving the kinetic mechanism of methanol pyrolysis and combustion.