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Preparation And Performances Of MOFs-Derived Fe Catalysts For CO2 Hydrogenation To Light Olefins

Posted on:2021-03-22Degree:MasterType:Thesis
Country:ChinaCandidate:Z C DongFull Text:PDF
GTID:2491306548977889Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
The production of light olefins(C2=-C4=)by CO2 hydrogenation is one of the important ways of CO2 utilization and efficient conversion,and the preparation of high-activity and high-selectivity catalysts is the key technology that restricts the progress of CO2 hydrogenation.Iron-based catalysts have attracted widespread attention due to their high activity in both re Verse water gas reaction(RWGS)and Fischer-Tropsch reaction(FTS),and their selective production of light olefins.Howe Ver,complicated reaction mechanism and phase change have always been a challenge to regulate performance of the reaction.The reasonable matching of the RWGS and FTS reaction rates is the biggest challenges to achie Ve high selectivity for the production of light olefins.Therefore,constructing a multi-component synergistic catalyst and effectively connecting two-step reactions in series is the key to improving the selectivity of light olefinss.Different iron salt precursors(FeCl3·6H2O、Fe(NO33·9H2O、Fe(acac)3)were introduced to prepare FeZn/NC catalysts and study the effect of precursor types and loading methods on the catalyst structure-activity relationship.The results showed that the FeZn/NC-3 catalyst derived from Fe(acac)3 exhibits the best light olefins selectivity(11.24%)and CO2 conversion reached 14.35%,which may be related to the unique cage structure it forms.Howe Ver,the Fe3C formed during the reaction of the carbon-supported FeZn bimetallic catalyst was not conducive to the conversion of the FTS process,resulting in high selectivity of CO and inhibiting the positive conversion of CO2.Pyrolysis of ZIF-67 at different temperatures to obtain carbon-encapsulated FeCo/NC catalysts.Cobalt was introduced to enhance the activity of the reaction,which can better coordinate the two-step reaction.It was found that the reaction activity of the cobalt-iron bimetallic catalyst has been greatly improved,and the NC layer forms by pyrolysis of cobalt-iron bimetallic catalyst at high temperature can effectively anchor and disperse metal nanoparticles.The type and content of the iron active phase were determined by M(?)ssbauer spectroscopy.The results showed that a higher pyrolysis temperature was beneficial to the formation of iron carbide phase.In addition,part of the metal cobalt was converted to Co2C,which promoted the conversion of the intermediate product CO to light olefins.FeCo/NC-600exhibited the best selectivity of light olefins(27.05%),while its CO2 conversion reached 37.03%.In order to more reasonably adjust the reactive site of FTS and further improve the selectivity of light olefins,FeCo/MC catalysts with controllable metal ratio were constructed with Fe-MOF as the main body and terephthalic acid as the framework ligand.,and clarified the synergistic effect of bimetal and the effect of bimetal ratio on the reaction results.It was found that the addition of Co can effectively increase the basic sites on the catalyst surface,thereby effectively improving CO2 adsorption.On the other hand,the addition of Co can effectively promote the carbonization process of iron and promote the positive progress of RWGS through the CO consumption of the FTS path.In addition,proper metal ratio helps to improve the proximity between iron and cobalt,which cooperatively catalysed a tandem reaction to obtain the best light olefins selectivity and the lowest methane selectivity as possible.FeCo(6:1)/MC exhibited the highest selectivity of light olefins(37.14%),while its CO2 conversion reached 32.72%.
Keywords/Search Tags:CO2 hydrogenation, Fe based catalysts, MOFs, M(?)ssbauer spectroscopy, Pyrolysis, Light olefins
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