Theoretical investigation for the cycle reaction of methane oxidation catalyzed by FeO<sup>+</sup> in the gas phase

Abstract

The mechanism of the spin-forbidden reaction of CH4 with O2 catalyzed by FeO+ (6Σ+, 4Π+) on both quartet and sextet potential energy surfaces has been investigated at the B3LYP level of theory. Six competitive reaction pathways for the catalytic reaction and Path 6 are likely in competition with other pathways from energetic viewpoint. There are 6 crossing points in Path 6 and the crossing points 1 and 3 are very important. The minimum energy crossing points (MECP) of corresponding crossing points are optimized. The potential energy surfaces and the possible spin inversion processes are discussed by means of spin-orbit coupling (SOC) and probability of intersystem crossing (ISC) calculations. The SOC of MECP1 is 947.58 cm-1, and MECP3 is 1372.51 cm-1. The probability of ISC are 0.535 and 0.590 respectively. In order to understand the competitive reaction mechanism involving H atom transfer, the activation strain model was adopted for a simple analysis of the competitive reaction. The energetic span ( δE ) model coined by Kozuch is applied in this cycle. X TOF (degree of TOF control) of all of transition state and intermediate are calculated, and the turnover frequency (TOF)-determining transition state (TDTS) and TOF-determining intermediate (TDI) are confirmed. In this catalytic reaction, the TOF is 5.6716×10-42 s-1.