Predictive kinetics on the formation and decomposition of ethylbenzene

The kinetics of reactions over the ethylbenzene surface were studied by using ab initio transition state theory (TST) based master equation methodologies. The variable reaction coordinate TST (VRC-TST) approach was employed to obtain high pressure limit rates for barrierless channels, including C7H7 + CH3, C6H5 + C2H5, C6H5CHCH3 + H, and C6H5CH2CH2 + H. Interaction potentials between each pair of fragments were simply simulated with CASPT2/cc-pVDZ calculations and scaled by reference to QCISD(T)/CBS energies. The larger basis set, cc-pVTZ, was tested to have only a very limited improvement on the final kinetics. For benzyl + CH3 recombination, addition to benzylic-site forming ethylbenzene dominates overwhelmingly over addition to ortho- and para-sites forming o-methylbenzyl and p-methylbenzyl, respectively. For C6H5CHCH3 + H recombination, addition to benzylic-site also dominates over addition to sites at the aromatic ring. Present predictions, from a theoretical perspective, demonstrate strong preference for the CC dominance in ethylbenzene decomposition. The quite good agreement with earlier studies lend confidence to present predictions. More importantly, our kinetic predictions imply that it could probably introduce large uncertainties if simply using kinetic parameterizations of toluene in modeling study of larger alkylbenzenes. The ethylbenzene system should serve as a better and safer reference.