Study On CO₂ Conversion Using Dielectric Barrier Discharge Plasma At Atmospheric Pressure

The concentration of CO2 in the atmosphere continues to increase,and the greenhouse effect caused by it has become a global environmental problem.At the same time,as a kind of rich carbon resource,the development and utilization of CO2 is of great significance.Due to the stable structure of the CO2 molecule,it is most critical to achieve CO2 activation.Low temperature plasma can generate high-energy electrons and active particles,which can activate gas molecules at normal temperature and pressure,improving the activity of chemical reactions.The low temperature plasma technology provides a new idea for CO2 conversion under atmospheric pressure,decomposing CO2 into CO with high added value.In this paper,the conversion of CO2 via dielectric barrier discharge?DBD?plasma was studied.In the coaxial cylindrical DBD reaction device,the impact of multiple factors on CO2 conversion and energy efficiency during the reaction process were examined;and a packed bed in the DBD plasma reaction system was built,in which gap different dielectric materials and g-C3N4catalyst were filled,and the influence of the filling materials on the CO2 conversion was explored.The main research work and results are as follows:?1?The research of CO2 conversion via DBD plasma was carried out.In the coaxial cylindrical DBD reactor,the morphology and material of the high-voltage electrode affected the discharge characteristics and the conversion effect of CO2.When using rod,coil or powdery high-voltage electrodes for discharge,the discharge properties did not change.During the discharge process using powdery high-voltage electrodes,the discharge intensity was large,the amount of transferred charge was much,and the CO2 conversion rate and energy efficiency were high.When the copper powder material with good conductivity was used as the high-voltage electrode,the discharge intensity was large,and the CO2 conversion rate,the CO yield and the energy efficiency reached 9.2%,9.0%,and 8.2%,respectively.The influence of temperature,power and gas supply parameters on the conversion of pure CO2 was investigated.The results showed that:under the stable discharge,the discharge frequency basically did not affect CO2 conversion;increasing the input power or reducing the gas flow rate improved the CO2 conversion rate and CO yield,and the energy efficiency showed the opposite trend;adding a circulating water cooling device outside the reactor could effectively reduce the temperature of the reaction system,thereby suppressing the reverse reaction of CO2 decomposition,which was beneficial to CO2 conversion,and the maximum CO2 conversion rate was 14.3%under cooling.Introducing N2 into the reaction system was beneficial to improve CO2 conversion rate.In the mixed atmosphere,the higher N2concentration generated the better conversion result.When the N2 concentration was 50%,the CO2 conversion rate reached up to 26.3%.Via the CO2 plasma emission spectrum,the decomposition of CO2 was mainly caused by the collision of high-energy electrons.?2?The effect of dielectric materials on CO2 conversion in the packed bed DBD system was studied.In the experiment,?-Al2O3 spheres,glass beads and activated carbon particles were filled as dielectric materials in the discharge gap.The discharge form was changed from filamentous discharge to filamentary discharge combined with surface discharge.Adding dielectric materials was conducive to promoting the transfer of charge and increasing the discharge intensity.The?-Al2O3 pellets and activated carbon particles with porous structure could adsorb CO2 gas and decompose it on the surface of the material.The maximal CO2conversion rate when filling?-Al₂O₃ pellets was 11.1%.Activated carbon could react with O,inhibiting the reverse process of CO2 decomposition,and thus promoted CO2 conversion.The maximal CO2 conversion rate when filling activated carbon was 12.0%.The glass beads with smooth surface structure were helpful to enhance the surface discharge between the glass beads and improve the activity of the chemical reaction.The maximal conversion rate of CO2filling glass beads was 11.3%.?3?The catalytic effect of g-C3N4 catalyst in the packed bed system on CO2 conversion was studied.In the packed bed DBD plasma,g-C3N4 catalyst showed good catalytic activity.During the preparation process,the type and amount of precursor affected the catalytic effect.Compared with the m-g-C3N4 catalyst prepared by the melamine precursor,the u-g-C3N4prepared by the urea precursor had larger specific surface area,which provided more reaction sites for CO2 decomposition,and the CO2 conversion result was better.When filling u-g-C3N4in the reaction gap,the maximal CO2 conversion rate,CO yield and energy efficiency was17.2%,16.5%,and 20.0%,respectively.Adding the quantity of the precursor increased the number of microdischarges generated during the discharge process,thereby enhancing the activity of the chemical reaction.Doping K in g-C3N4 formed K-N between the sheets of the catalyst,improving the photoresponse range of the catalyst and the separation efficiency of photogenerated carriers,and the catalytic effect of the CO2 conversion process was further enhanced.When filling K/u-g-C3N4 catalyst,CO2 conversion rate reached up to 19.3%.