Design Of Plasma Microdischarge Space And Defect Regulation Of CO₂ Decomposition Catalyst

Plasma catalysis is a very promising industrial and environmental catalytic decarbon solution based on renewable energy.The combination of NTP technology and heterogeneous catalyst has always been focus of research on CO₂conversion.In this work,a water-cooled coaxial dielectric barrier discharge（DBD）reactor with an operable packed bed configuration was developed for the decomposition of pure carbon dioxide.By designing the microdischarge space of ZnO based packing materials,the synergistic mechanism of physical discharge and catalysis was discussed.The effects of dielectric and conductive layers were discussed from the perspective of gas diffusion.The performance of ZnO based packing materials was improved through metal doping in CO₂conversion.The detailed research is as follows:（1）Study on regulation of DBD plasma microdischarge space and the packing performance of different metal semiconductor oxide microspheres in DBD plasma of carbon dioxide.The DBD plasma was optimized and the best DBD parameters（discharge gas 6 mm and discharge length 12 cm）were selected for subsequent experiments.The packing test of different metal semiconductor oxide microspheres（ZnO,ZrO₂,NiO,SnO₂）was carried out in the adjusted DBD plasma system,and the reaction effect of ZnO microspheres was the best（At the highest input power of 110 W and the lowest inlet flow rate of 20m L/min in this experiment,the CO₂conversion rate was the highest at 33.45%.At the lowest input power of 30 W and the highest inlet flow rate of 100 m L/min,the energy efficiency was the highest at 7.65%.）.The effects of discharge power and gas feed velocity on CO₂conversion were consistent with the results of all conventional DBD.The CO₂conversion increased with the increase of system input energy,while the energy efficiency of DBD process decreased.（2）Discharge effect and catalytic effect dominated the competition-the difference of reaction properties of different materials at different flow rates.In this paper,ZnO nanocomposites（ZnO-S@NF and ZnO-F@NF）were prepared by simple hydrothermal method on the basis of nickel foam with good electrical conductivity.Using four samples of without packing,nickel foam unloaded,ZnO-S@NF and ZnO-F@NF as control,SIE,input power and flow rate were set respectively to conduct CO₂conversion performance test and electrical signal recording.Experimental results show that the flow rate of feed gas is the most critical factor affecting the reaction performance.In the process of rising the flow rate,the discharge effect and catalytic effect of materials were in competition for dominance.At a lower flow rate（20-55 m L/min）,the nickel foam expands the electrode,which makes the electric field strength of the DBD reaction.The reaction effect of nickel foam is better than that of ZnO@NF.The catalytic effect plays a leading role when flow rate increases（over 55 m L/min）.The CO₂conversion rate（15.6%）and energy efficiency（4%）of the ZnO@NF-packed DBD at the input power of 70 W and the flow rate of 80 m L/min were 1.3 and 1.1 times higher than those of the foam nickel packed DBD（12.3%and 3.48%）.The characterization results show that the existence of oxygen vacancy in ZnO nanocomposites promotes the catalytic reaction.The DFT calculation inferred that the presence of oxygen vacancy under plasma conditions reduced the activation energy of the reaction.（3）Metal cation doping introduces defects in ZnO nanocomposite materials to improve the catalytic performance of carbon dioxide DBD plasma reaction.In the conclusion of the second part,the critical flow rate of the catalytic reaction is obtained.After the critical value,the catalytic performance of the material is no longer limited by mass transfer.Therefore,in the third part,the catalyst is designed and its defects are regulated to achieve the purpose of controlling the catalytic rate.ZnO@NF,Fe-ZnO@NF,In-ZnO@NF and Cu-ZnO@NF were prepared by simple hydrothermal method and tested at high flow rate.Experimental results are consistent with DFT simulation calculation results,Cu-ZnO@NF showed the best reaction effect（CO₂conversion rate is 35%,energy efficiency is 11%）,in which oxygen vacancy content（53%）was the highest.The interaction between oxygen vacancy and DBD improves the catalytic performance of the reaction,and the DFT calculation also confirms that oxygen vacancy formation energy of Cu²⁺doping is the lowest.