Product Identification in the Low-Temperature Oxidation of Cyclohexane Using a Jet-Stirred Reactor in Combination with SVUV-PEPICO Analysis and Theoretical Quantum Calculations

Cyclohexane oxidation chemistry was investigated using a near-atmospheric pressure jet-stirred reactor at T = 570 K and equivalence ratio ? = 0.8. Numerous intermediates including hydroperoxides and highly oxygenated molecules were detected using synchrotron vacuum ultraviolet photoelectron photoion coincidence spectroscopy. Supported by high-level quantum calculations, the analysis of photoelectron spectra allowed the firm identification of molecular species formed during the oxidation of cyclohexane. Besides, this work validates recently published gas chromatography and synchrotron vacuum ultraviolet photoionization mass spectrometry data. Unambiguous detection of characteristic hydroperoxides (e.g., gamma- ketohydroperoxides) and their respective decomposition products provides support for the conventional O-2 addition channels up to the third addition and their relative contribution to the cyclohexane oxidation. The results were also compared with the predictions of a recently proposed new detailed kinetic model of cyclohexane oxidation. Most of the predictions are in line with the current experimental findings, highlighting the robustness of the kinetic model. However, the analysis of the recorded slow photoelectron spectra indicating the possible presence of C-5 species in the kinetic model provides hints that the substituted cyclopentyl radicals from cyclohexyl ring opening might play a minor role in cyclohexane oxidation. Potentially important missing reactions are also discussed.

Automated summary

The oxidation chemistry of cyclohexane was studied under near-atmospheric pressure conditions, revealing various intermediates and molecular species formed during the oxidation process through synchrotron vacuum ultraviolet photoelectron photoion coincidence spectroscopy. The results were supported by high-level quantum calculations and compared with existing gas chromatography data, validating the robustness of the kinetic model. Some hints of potential missing reactions, such as the role of substituted cyclopentyl radicals in cyclohexane oxidation, were also discussed based on the analysis of slow photoelectron spectra.