Study On Carbon Dioxide Methanation Performance Of Low Loading Ce Modified Ni Based Catalyst

Energy and environment are the important foundation of social development and people’s livelihood economy.On the one hand,since the industrial revolution,with the combustion of fossil fuels,a large amount of CO₂ has been released into the atmosphere,resulting in greenhouse effect and a series of environmental problems;On the other hand,fossil energy is non renewable and the total amount is limited.At present,human demand for fossil energy is still rising,and the reserves of fossil energy will eventually be exhausted.In this regard,China has made a commitment to the"double carbon"goal.Therefore,it is urgent to convert and reuse CO₂.CO₂ methanation,which can not only synthesize methane to alleviate the energy supply crisis,but also reduce carbon emissions and realize carbon neutralization,has attracted extensive attention.The core of CO₂methanation reaction is catalyst.At present,the main problems faced by CO₂ methanation catalyst are poor low-temperature activity,easy high-temperature sintering and carbon deposition deactivation.Therefore,the key to CO₂ methanation is how to design and construct a low-temperature,efficient and stable catalyst.In this thesis we studied the morphology control and auxiliary modification of Ni based catalyst,and improved the low-temperature activity of the catalyst by magnetron sputtering and atomic layer deposition.The main research contents are as follows:（1）The controllable preparation of Ce doped mesoporous desert rose shaped nickel magnesium mixed metal oxide catalyst was realized by adjusting the reaction time,surfactant type and addition amount of solvothermal method.The experimental results show that Ni mg mixed metal oxides contain a large number of mesopores and have good thermal stability.Doping Ce into them can improve the low-temperature activity of the catalyst for carbon dioxide methanation.Ce doping can reduce the grain diameter of catalyst Ni particles,increase the specific surface area and pore volume of the sample,increase the number of medium alkaline sites and increase the proportion of defective oxygen on the catalyst surface.The CO₂ conversion of Ni3Mg1Ce0.03 catalyst reached 85.6%at 250℃,91.7%at 300℃,and the CH₄ selectivity reached 93.2%.There was no deactivation in the 60 h stability test.（2）Ce was deposited on the surface of the catalyst by magnetron sputtering technology to construct the Ni Ce species interface and improve the low temperature activity of the catalyst.The CO₂ conversion and CH₄selectivity of the catalyst prepared by magnetron sputtering for 6 h reached 83.0%and 90.6%at 250℃.Doping Ce by magnetron sputtering can reduce the grain diameter of Ni particles and enhance theα-The reducibility of Ni O increases the number of basic sites of the catalyst.However,when magnetron sputtering technology is used to deposit metal on powder materials,there are still problems of uneven deposition and unable to go deep into the interior of the channel,resulting in a waste of some Ce resources,and the content of Ce on the catalyst still needs to be further reduced.（3）In order to further improve the dispersion of Ce and improve the atomic utilization of Ce,atomic layer deposition technology was applied to the preparation of CO₂ methanation catalyst.It was found that doping low content of Ce on the surface of the catalyst by atomic layer deposition technology could effectively improve the low-temperature catalytic performance of the catalyst,and the performance increased with the increase of atomic layer deposition cycles.Atomic layer deposition has effectively improved the problem of uneven magnetron sputtering deposition and achieved high dispersion.The Ce content of the catalyst for 300cycles of atomic layer deposition is 0.24‰,but it can achieve 89.8%CO₂ conversion and 89.5%CH₄selectivity at 300℃.Atomic layer deposition technology does not change the microsphere structure of the catalyst.Through characterization,it is found that the introduction of Ce through atomic layer deposition can improve the interaction between the activity and the support,enhance the stability of the catalyst,increase the number of basic sites of the catalyst,and generate more surface oxygen vacancies.