Thermal decomposition of ethanol. 4. Ab initio chemical kinetics for reactions of H atoms with CH3CH2O and CH3CHOH radicals

Z. F. Xu, Kun Xu, Ming-Chang Lin

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Abstract

The potential energy surfaces of H-atom reactions with CH 3CH2O and CH3CHOH, two major radicals in the decomposition and oxidation of ethanol, have been studied at the CCSD(T)/6-311+G(3df,2p) level of theory with geometric optimization carried out at the BH&HLYP/6-311+G(3df,2p) level. The direct hydrogen abstraction channels and the indirect association/decomposition channels from the chemically activated ethanol molecule have been considered for both reactions. The rate constants for both reactions have been calculated at 100?3000 K and 10 ?4 Torr to 103 atm Ar pressure by microcanonical VTST/RRKM theory with master equation solution for all accessible product channels. The results show that the major product channel of the CH3CH2O + H reaction is CH3 + CH2OH under atmospheric pressure conditions. Only at high pressure and low temperature, the rate constant for CH3CH2OH formation by collisonal deactivation becomes dominant. For CH3CHOH + H, there are three major product channels; at high temperatures, CH3+CH2OH production predominates at low pressures (P < 100 Torr), while the formation of CH3CH 2OH by collisional deactivation becomes competitive at high pressures and low temperatures (T < 500 K). At high temperatures, the direct hydrogen abstraction reaction producing CH2CHOH + H2 becomes dominant. Rate constants for all accessible product channels in both systems have been predicted and tabulated for modeling applications. The predicted value for CH3CHOH + H at 295 K and 1 Torr pressure agrees closely with available experimental data. For practical modeling applications, the rate constants for the thermal unimolecular decomposition of ethanol giving key accessible products have been predicted; those for the two major product channels taking place by dehydration and C?C breaking agree closely with available literature data.

Original languageEnglish
Pages (from-to)3509-3522
Number of pages14
JournalJournal of Physical Chemistry A
Volume115
Issue number15
DOIs
StatePublished - 21 Apr 2011

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