Study On The Design,preparation And Catalytic Performance Of Layered K-Fe-M Catalysts For CO₂ Hydrogenation To Light Olefins

CO2 is the cheapest and most abundant carbon resource.Under mild conditions,CO2 reacts with hydrogen to form various chemical materials or chemicals such as CH4,CH3OH,light olefins(C2=-C4=),a-olefins,and oxygenates.Light olefins are important basic chemical raw materials,which can be obtained by CO2 hydrogenation through Reverse Water Gas Shift and Fischer-Tropsch Synthesis reaction,which is one of the research hotspots in this field.Fe-based catalysts are the main catalytic system currently because of their high Water Gas Shift,Fischer-Tropsch synthesis activity and high olefin selectivity.Further modified by additions,the target product can be synthesized with high selectivity,and the research is more in-depth and extensive.Due to the limited ASF distribution of Fischer-Tropsch synthesis products,the selectivity of light olefins is difficult to increase,and the design of high-performance catalysts is the key.In this paper,a modified layered multi-component Fe-based catalyst was designed and prepared for the purpose of inhibiting the secondary reaction of olefins,increasing the selectivity of olefins and controlling the distribution of products.Through the design of the layered catalyst,combined with the characterization of the catalyst,the effects of catalyst structure,composition and surface properties on the catalytic performance of CO2 hydrogenation to low-carbon olefins were investigated.The main contents of the completion are as follows:1.A series of Zn modified layered K-Fe-Zn-Ti catalysts were prepared by high temperature solid phase reaction for direct hydrogenation of CO2 to olefins.The catalysts were characterized by SEM,TEM,XRD,H2-TPR,CO2-TPD and XPS.The results show that the catalysts are all formed K2.3Fe2.3Ti5.7O16 phase,which is a typical layered metal oxide(LMO)structure.After Zn modification,the ZnFe2O4 phase appears,which reduces the crystallinity of the sample.Zn promoter can enhance the alkalinity of the catalyst surface and promote the adsorption of CO2 surface.In the CO2 hydrogenation reaction,the series catalysts of K-Fe-Zn-Ti have higher olefin selectivity(O/P>6.5),Zn modification promotes C5-formation,and significantly increases the selectivity of C4+ linear a-olefins(LAOs).The content of LAOs in C4+ hydrocarbons is 54.6%increased to 75.2%;Within the ratio range investigated,as the Zn/Fe ratio increases,the alkane/olefin(O/P)value of low carbon(O2=-O4=)increases first and then decreases,but the heavy hydrocarbon content and LAOs selectivity do not affect significantly;the catalyst remained LMO structure after 100 h on-line reaction,and the stability was good.2.In order to achieve the synergy of the two-step reaction and further reduce the formation of by-product CO,a series of Fe/K-Zn-Ti catalysts with different Fe contents were prepared by impregnation method.In the CO2 hydrogenation reaction;the LMO structure was mainly K80Zn40Ti1.6O4 phase.After impregnating Fe,the crystallinity of the sample and the regular layer structure are reduced;As the Fe content increases,the surface of the catalyst increases in alkalinity;In the CO2 hydrogenation reaction,the catalyst 15%Fe/K-Zn-Ti lower olefins reached 51.1%,the O/P value was 7.2,and the CO selectivity decreased to 47.7%;The catalyst showed good stability after being reacted online for 100 h.