Kinetic study of CH3OCH3/CO2 reforming in a nanosecond pulsed discharge

The chemical kinetics of CO₂ reforming of dimethyl ether (DME) is explored experimentally and numerically. Experiments are conducted in a flow reactor (DME/CO₂/Ar, 340K, 30 Torr) with a nanosecond pulsed dielectric barrier discharge (DBD). Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) is employed to achieve the species measurement in this system. Nine ions are observed, including CH₃⁺, O⁺, Ar²⁺, CO⁺, CHO⁺, Ar⁺, CO₂⁺, CH₃OCH₂⁺, and CH₃OCH₃⁺. Several intermediate species and products are identified based on the mass spectra and photoionization efficiency (PIE) spectra, such as methane (CH₄), water (H₂O),carbon dioxide (CO), formaldehyde (CH₂O), methanol (CH₃OH), ketene (CH₂CO), ethyl methyl ether (C₂H₅OCH₃), methyl formate (CH3OCHO), and dimethoxymethane (CH₃OCH₂OCH₃). Species mole fraction profiles as a function of inlet CO₂ concentrations are obtained with the inlet CO₂ varying from 3% to 18% in the DME/CO₂/Ar mixture (n_DME=3%). The consumption of DME is promoted with the addition of CO₂, and the mole fractions of some products such as H₂O, CO, CH₃OH, MF, and DMM increase firstly and then decrease. A kinetic mechanism incorporating plasma reactions and combustion reactions is developed for this system, and its prediction performance is tested against the experimental data. Rate of production (ROP) analysis indicates that DME is consumed through two channels, the H-atom abstractions with O/H/OH radicals and dissociations with plasma activated species such as electrons, Ar⁺, and Ar^*. With the increase of the inlet CO₂ mole fractions, the former pathways are enhanced and the latter channels are weakened. The dissociation reactions with electrons and Ar* and ionic reactions account for most of the CO formation, and H-atom abstraction reaction of DME and CHO radical by H radical are responsible for the H₂ formation. The oxygnated species like CH3OCHO is generated from reactions of peroxides, while C₂H₅OCH₃ and CH₃OCH₂OCH₃ are formed through radical recombination.