Global Modeling On Reaction Mechanism Of Dry Reforming Of Methane In Atmospheric Pressure Non-equilibrium Plasma

Methane is a promising energy source.The conversion of methane into value-added liquid chemicals and syngas,such as dry reforming of methane,partial oxidation of methane,and etc.,is becoming a hot research topic.Recently,atmospheric non-equilibrium plasma has been proposed as a potential and novel type of“reaction carrier”for the activation and conversion of greenhouse gases（methane and carbon dioxide）into value-added chemicals,due to its unique non-equilibrium characteristics.In this paper,a zero-dimensional chemical reaction kinetic model in CH₄/CO₂ gas mixture is constructed,with an emphasis on reaction mechanism for plasma dry reforming of methane to syngas and oxygenates.Especially,the effect of the CH₄ molar fraction（5%-95%）on plasma dry reforming of methane is investigated.First,the time evolution of electron temperature and density with initial methane content is presented,and the results show that a higher initial methane content in gas mixture is favored for a larger electron temperature and density.Subsequently,the time evolution of number densities of free radicals,ions and molecules at different CH₄/CO₂ molar fraction are given.Conversions of inlet gases,selectivities of syngas and important oxygenates are also calculated.Moreover,the dominant reaction pathways governing production and destruction of H₂,CO,CH₂O and CH₃OH are determined,and CH₃ and OH radicals are found to be the key intermediate for the production of valuable oxygenates.Finally,a schematic overview of the transformation relationship between dominant plasma species is summarized and shown to clearly reveal intrinsic reaction mechanism of dry reforming of methane in atmospheric non-equilibrium plasma.Besides,a two-dimensional fluid model is also constructed to study the reaction mechanism of plasma CO₂ hydrogenation in atmospheric-pressure dielectric barrier discharge（DBD）.The effect of varying volume ratio of CO₂/H₂ on reaction mechanism of CO₂ hydrogenation is studied carefully,such as temporal and spatial density distributions of main radicals and ions,dynamics of streamer propagation,and generation and loss pathways of H,CO,and CH₃OH.It is found that H,O and CO are the three most abundant species,and lower hydrogen content in gas mixture promotes streamer propagation and formation of conduction current in plasma column.Besides,H is mainly produced by electron-impact dissociation of H₂（e+H₂→e+2H）,O and CO are dominantly produced by electron-impact dissociation of CO₂（e+CO₂→e+CO+O）.Interestingly,H addition reaction to intermediate specie CH₃O（CH₃O+H→CH₃OH）is found to be the main reaction pathway for methanol formation.