Theoretical study on COS oxidation mechanism

Abstract

COS is the most abundant sulfur containing compound in the atmosphere that could cause serious adverse effects on human health and environment. Understanding the oxidation mechanism of COS is with great significance in controlling and utilization reduced sulfur (CS2 and COS). In this study, density function theory (DFT) and multi-reference configuration interaction with Davidson correction (MRCI+Q) methods were adopted to investigate the oxidation mechanism of COS. All energies were refined at CCSD(T)/CBS level and subsequently used to deduce the kinetic parameters. The critical mechanism was validated by experiments results. It was found that the oxidation of COS is initiated through three channels. In COS+COS channel, S2(a1∆g) is first produced and then oxidized to SO(X3Σ). In COS+O2 channel, COS combines O2(X3Σg) to yield SO(X3Σ, a1∆) and CO2(X1Σg). In COS dissociation channel, atomic sulfur S(3P, 1D) will be primarily generated and subsequently oxidized to SO(X3Σ) and O(3P). Oxidation of SO(X3Σ) could either result in O(3P) formation. At higher COS concentration, O(3P) formed through three initiation channels will react with COS to produce S(3P) and SO(X3Σ), both of which will be oxidized finally to SO2(X1A1) to reproduce O(3P). Reaction of COS+O(3P) is the dominating consumption reaction of COS. The major products of COS oxidation are CO(a1∆) and CO2(X1Σg) and SO2(X1A1). The ratio of CO/CO2 in products is mainly affected by the branching fraction of COS+O(3P). Based on the rate coefficient calculated at CCSD(T)/CBS level, a comprehensive kinetic model was developed to predict the COS oxidation process. The modeling results are in agreement with experiment data.