Preparation Of Molecular Sieve Functional Materials From Kaolinite Tailings And Their CO₂ Catalytic Performance

The massive accumulation of tailings and excessive CO₂emissions are responsible for serious environmental problems and extreme weather conditions,which greatly threaten the survival and development of human beings.With the further acceleration of China’s economic development from high-speed growth to high-quality development.Solving the contradiction between tailings and CO₂ and social development has become an important starting point for the country to achieve strategic energy expansion and the game of great powers to occupy the commanding heights,in the context of“carbon neutrality”.At present,CO₂-methane dry reforming,CO₂-methanation and CO₂-assisted ethane oxidative dehydrogenation are the most promising three technical approaches and conceptual methods applied to CO₂ conversion and utilization.Using tailings as raw materials to prepare functional catalysts that can be used for efficient CO₂ conversion can maximize the realization of the goal of“treating waste with waste”.Based on this vision,in this paper,typical silicon-rich solid waste kaolinite tailings were used as raw materials to prepare highly active functional catalysts for CO₂ conversion through the assembly of different active components.The mechanism of its transformation in the reaction process was also studied.The specific research ideas and contents are as follows:Adopt the method of mechanical ball grinding activation and acid and alkali treatment for primary treatment was conducted on the kaolinite tailings,extract the useful composition of tailings,was prepared by hydrothermal synthesis method has a special“flower ball”morphology of ZSM-5 microporous molecular sieve,and the materials used in the conversion of CO₂ using high-performance catalyst preparation,successfully develop the high value of tailings utilization way.Ni Ru_xCZZ5 catalyst,which can be used for dry reforming of CO₂ and methane,was prepared by ultrasonic assisted impregnation process with kaolinite tailings as raw material.The effect of inactive components on catalytic performance was studied,and the reaction mechanism was investigated.The results show that the special morphology of ZSM-5 can anchor the active component and strengthen the interaction between the active metal and the support.The Ni Ru_0.5CZZ5 catalyst showed excellent initial activity and stability,with CO₂ and CH₄ conversion rates reaching100%and 95.6%at 800℃.The stability test performance of the smaller GHSV(30,000 m L g_cat^-1 h^-1)showed almost no decline within 30 h.Stability tests at 100 h for the larger GHSV(30,000 m L g_cat^-1 h^-1)showed no significant catalytic inactivation.The in-situ diffuse reflection technique was used to investigate the reaction mechanism.The polymetallic co-catalysis and the shape selection catalysis of the carrier are the important reasons for the excellent catalytic performance.Based on the silicon-rich characteristics of kaolinite tailings,Ni/ZSM-5@MCM-41 multiporous catalytic materials were prepared to study CO₂methanation by constructing Si O₂ multiporous materials with core-shell structure.The effects of different substrate materials（ZSM-5,MCM-41and ZSM-5@MCM-41）on the methanation performance of CO₂ were compared.It was found that the combination of the high specific surface area of MCM-41 and the natural hydrophobicity of ZSM-5 can effectively prevent the catalytic encapsulation of H₂O generated in the CO₂methanation process,which can reduce the inhibitory effect of H₂O on forward catalytic reaction.Therefore,Ni/ZSM-5@MCM-41 catalyst showed excellent catalytic performance,CO₂ conversion and CH4selectivity can reach 80%and 97%at 400℃.In addition,Ni/ZSM-5@MCM-41 also demonstrated excellent reaction stability at 80 h continuous reaction test,with almost no carbon deposition.It is confirmed by infrared technology that Ni metal catalyst on multi-porous support follows the reaction path of formate species and CO as intermediates in CO₂ hydrogenation.A series of Cr-Ce/ZSM-5 catalysts for CO₂ assisted ethane oxidative dehydrogenation was prepared by functionalizing the“flower ball”ZSM-5 zeolite based on tailings,using Cr and Ce as active components of metal oxides.The folds and grooves on the surface of the carrier give the material a natural interface limiting effect,which provides a good landing site for the loading of the active component to better anchor Cr and Ce metal oxides,resulting in a strong interaction between the active component and the carrier.The influence of Cr-Ce ratio on catalytic performance was studied.The results show that the appropriate Cr-Ce ratio is the key to determine the content of Cr⁶⁺in the active phase.The 5%Cr-10%Ce/ZSM-5 catalyst has the largest relative content of Cr⁶⁺species.The conversion rate of C₂H₆ and selectivity of C₂H₄ maintained 74%and 80%of the initial values within 30 h at 800℃.Because a large number of Cr⁶⁺species enhanced the binding ability of the catalyst to active oxygen species,and promoted the generation and gasification process of carbon deposition on the catalyst surface,5%Cr-10%Ce/ZSM-5 also showed excellent anti-carbon deposition ability.