Theoretical Investigation of the Oxidation of Propane by FeO+

Abstract

We report herein a comprehensive theoretical study of the oxidation of propane by FeO(+) on both the sextet and quartet potential energy surfaces (PESs) using density functional theory. The geometries and energies of all the stationary points involved are located. Interaction of FeO(+) with propane could account for four types of encounters (i.e., alpha,beta,gamma-, 2alpha,beta-, 3alpha-eta(3), and 2alpha,2gamma-eta(4)) complexes. Various mechanisms leading to the loss of CH(3), H(2)O, C(3)H(7)OH (H(2)O + C(3)H(6)), and C(3)H(6) are analyzed in terms of the topology of the PES. The reaction of FeO(+) with propane involves initial C-H activation, while initial C-C activation is indeed unlikely to be important. The loss of CH(3) takes place adiabatically on the sextet PES via the simple C(alpha)-to-O H shift from eta(4)-OFe(+)(C(3)H(8)) followed by CH(3) shift. The C(3)H(7)OH elimination proceeds via direct C(alpha)-to-O H shift followed by C-O coupling, while the loss of H(2)O, C(3)H(6), and (H(2)O + C(3)H(6)) proceeds via the alpha,beta-H and beta,alpha-H abstraction mechanisms from all the eta(3) complexes. The most favorable channel is the alpha,beta-H abstraction mechanism for the H(2)O loss because it not only is energetically and dynamically favorable but also has a high crossing probability between the sextet and quartet PESs. The computational results are in concert with the available experimental information and add new insight into the details of the individual elementary steps.