Low-temperature Plasma Combined With Bismush-based Catalysts For Synergistic Conversion Of Carbon Dioxide

Under the background of carbon neutrality,it is urgent to solve various environmental problems caused by the increase of atmospheric CO₂ concentration.Since the CO₂ molecule with high bond energy of C=O is difficult to be activated,promoting the activation of CO₂ molecule is the key to enhance its conversion efficiency.Low temperature plasma technology can activate CO₂ at room temperature and atmosphere pressure.However,the resultantly active species in the plasma environment have low lifetime and are easy to quench,leading to the low conversion efficiency of CO₂.On the basis of the above considerations,we have designed and synthesized a series of Bi-based catalysts and introduced the dielectric barrier discharge plasma into the catalytic CO₂ system to enhance its conversion efficiency.The mechanism of synergic plasma catalysis and the effect of in-situ catalyst change on the catalytic process have been investigated.The main contents are as follows:（1）In view of the weak CO₂ adsorption capacity of catalyst and from the perspective of morphology regulation,a series of Bi₂O₃with different morphologies have been prepared by adjusting the solvents in the synthestic process to regulate the adsorption and activation capacity of CO₂ molecule.The influence of the morphologies of Bi₂O₃ catalysts on the performance of synergistic plasma catalysis of CO₂has also been systematically investigated.The results show that Bi₂O₃-H（H=hollow）,Bi₂O₃-MC（MC=multi-cavities）and Bi₂O₃-S（S=sphere）synthesized by solvothermal process have hollow,multi-cavities and spherical structures,respectively.Among these catalysts,Bi₂O₃-H has the highest activity at four different input powers and it has considerable energy efficiency（1.58%）and conversion efficiency（9.4%）at 40 W.The high specific surface area and strong CO₂ adsorption capacity of Bi₂O₃-H are the main reasons for the improvement of its synergistic plasma catalytic activity.（2）In view of that metal nanoparticles are easy to be oxidized under plasma conditions,the armor-type catalysts Bi@Bi₂O₃/C catalysts with core-shell structures have been constructed by in-situ pyrolysis of metal-organic-framework（MOF）.The results show that Bi@Bi₂O₃/C has high energy efficiency（2.31%）and conversion efficiency（10.8%）at 40 W and the conversion has no obvious change after 5 h of continuous reaction.The main reason of high conversion efficiency of CO₂ is that the mesoporous carbon in the catalyst can adsorb CO₂ molecule and the Bi₂O₃ layer on the catalyst surface can protect high-activity Bi nanoparticles from oxidation.（3）In view of the unclear catalytic mechanism in the process of synergistic plasma catalytic reaction and from the perspective of in-situ construction of material surface defects to investigate the effect of defects on catalytic activity,Bi OBr nanosheets have been prepared by hydrothermal method,and the change rule of surface oxygen defects and the CO₂ conversion efficiency of catalysts during the plasma catalytic reaction have systematically studied.The results showed that the CO₂ conversion efficiency is 15.8%at the initial stage of the reaction and reaches the highest value（27.6%）at 24 min,and remains at about 25%after 24 min.The main reason lies in the in-situ formation of oxygen defects in the original position of Bi OBr in the catalytic process.The appearance of oxygen defects leads to the change of adsorption mode of CO₂ molecules and the decrease of activation energy of reaction,which makes the catalytic reaction carry out through Mars-van Krevlen route.