Studies On The Interface Engineering Of Ni/MnO Catalysts And Plasma-assisted Catalytic CO₂ Methanation

The environmental problems caused by the massive emission of greenhouse gas CO₂and the energy crisis caused by the excessive use of fossil fuels are major threats to the development of human society.The realization of CO₂emission reduction and energy transition low-carbon development goals is the theme of today’s world.As a rich and important carbon source,CO₂is the basis of many chemical reactions.The use of hydrogen generated from renewable energy sources can effectively convert CO₂into high-value-added fuels and chemicals which will be a promising strategy for CO₂emission reduction.However,the traditional catalytic transformation of CO₂needs to be carried out under both high temperature and high pressure to acquire the ideal CO₂conversion and the yield of product which would be the bottlenecks that limit its industrial application.Non-thermal plasma（NTP）has been widely studied in CO₂catalytic reduction which would efficiently stimulate kinetic and/or thermodynamically limited reactions due to thermal imbalances such as high electron temperature and low heavy particle temperature,and can achieve efficient activation and conversion of molecules under low temperature and normal pressure conditions,which has received extensive attention from researchers.In addition,the introduction of catalysts into NTP can influence each other and complement each other,which can significantly improve energy utilization efficiency.Therefore,the coupled plasma-catalyzed CO₂methanation reaction can make full use of the high reactivity of the plasma and the high selectivity of the catalyst,as well as the synergistic effect of the two,to achieve high-efficiency catalytic conversion of CO₂.Based on this,this paper uses Ni/MnO as the catalyst to conduct basic research on the structure-activity relationship between the catalyst structure and the catalytic CO₂methanation performance in the plasma catalysis synergistic system.The preparation conditions are changed to directionally regulate the catalyst surface structural defects,and the catalyst morphology and physicochemical characteristics is systematically characterized.Combined with online mass spectrometry,the possible reaction paths of the Ni/MnO catalyst in cooperation with plasma catalyzed CO₂methanation are analyzed.The main content and conclusions of this article are as follows:（1）The structure of the catalyst Ni/MnO_xwas adjusted by reduction pretreatment,and the effect of the defect structure on the activity of plasma catalytic reduction of CO₂methanation was explored.Studies have shown that hydrogen plasma reduction pretreatment does not significantly improve the CO₂conversion rate and CH₄selectivity,but the product is almost completely CH₄under 500℃reduction conditions.Therefore,the best pre-reduction condition for the catalyst is to keep it at 500℃for 30 minutes.Through characterization and analysis,it is found that the supported manganese oxide is more sensitive to the reduction conditions.After the reduction treatment,the crystal structure of the catalyst is changed.During the reduction process,the chemical interaction between the Ni-Mnelements in the10Ni/MnO leads to the occurrence of the catalyst surface.The reconstruction resulted in different structural defects.The Raman test further confirmed the change of the local chemical environment on the catalyst surface.In addition,in the plasma coordinated catalysis process,the reduced 10Ni/MnO was used for catalytic CO₂hydrogenation under plasma conditions and traditional thermal catalysis tests.It was found that the reaction temperature after plasma discharge equilibrium has a limited effect on the reaction performance.（2）A series of Ni/MnO_xcatalysts with different Ni loadings（1,3,5,8 and 10wt%）were prepared by the co-precipitation method,and the Ni-MnO interface was further adjusted during the reduction pretreatment process to explore the plasma The optimal nickel loading for the catalytic CO₂methanation reaction further improves the interaction between the catalyst and the plasma and realizes the high-efficiency catalytic conversion of CO₂.The results showed that the CO₂conversion rate increased first and then slightly decreased with the increase of nickel loading.Among them,the 5wt%Ni/MnO catalyst showed the best CO₂conversion rate and CH₄selectivity.In addition,the combination of multiple characterization methods confirmed that during the pre-reduction process,due to the mutual conversion between the multivalent states of manganese oxide and the interaction between nickel and manganese,the Ni Mnalloy was formed on the surface of the 5Ni/MnO catalyst,which affected the surface charge of Mn-O.Distribution,significantly increase the number of surface oxygen vacancies,improve the low-temperature oxidation-reduction characteristics of the catalyst,thereby effectively promoting the improvement of CO₂conversion performance.（3）Through H₂and CO₂temperature-programming experiments,the effect of surface alkalinity of different nickel loading catalysts on CO₂adsorption and activation in the methanation reaction was explored.The results show that the medium-strength adsorption activation amount of CO₂on the surface of the 5Ni/MnO catalyst is significantly increased,indicating that the interaction between different nickel loadings and the support MnO forms different alkaline active sites,and more medium-strength alkaline in the catalyst The sites show higher CO₂catalytic reduction performance.（4）The product distribution of the DBD system filled with 5Ni/MnO during the reaction was analyzed by online mass spectrometry.Combined with the structure-efficiency analysis in the previous chapters,the plasma-catalyzed CO₂methanation reaction was proposed in the5Ni/MnO catalyst system.Possible reaction mechanism.In addition,the performance evaluation of CO₂conversion under different modes has been extensively studied under the control of different carriers,different morphologies,and different physical conditions.