Design,Preparation And Distribution Control Of CO Hydrogenation Products Of Layered MAG Supported Fe-based Catalyst

The use of coal,natural gas or biomass(cellulose,hemicellulose,lignin,etc.)to generate synthesis gas(syngas;CO and H2)provides a suitable approach to prepare olefins,since the synthesis of lower olefins from syngas is a short process with low equipment investment and high resource utilisation.In the system of direct conversion of synthesis gas to lower olefins,iron-based catalysts have greater competitive advantages than other metal catalysts.It is reported that without carrier dispersion,the particles are easy to sinter,and the mechanical stability of the catalyst is poor.The supported catalysts can theoretically realize the dispersion and solid loading of active components,reducing particle breakage caused by coking,and have better industrial application prospects.Magadite(MAG)is a kind of layered silicate.It has a unique layered structure and hydrophilicity,which contains hydroxyl and alkali metal additives.The advantages of this material are conducive to the diffusion of olefins and product regulation in FTS.This work embraces the MAG supported Fe based catalyst,through the preparation method,the particle size effect of Fe3O4 and the preparation of catalyst solvent effect to explore the influence of CO hydrogenation performance.The structure and surface properties of the catalysts were characterized by DRIFTS、XRD、BET、SEM、XPS、CO-TPD、CA、Zeta and H2-TPR methods.The relationship between the phase structure and surface properties of the catalysts and the product selectivity was explored.The main research contents and results are as follows:(1)The Fe/MAG catalyst was prepared by different methods.Compared with Fe3O4,the catalytic activity of the supported catalyst greatly reduced due to the active component covered by the surface structure of the support and the selectivity of CH4 reduced to about 17%.After loaded with MAG,the pore size of the catalyst becomes bigger and the steric hindrance effect decreases,which is due to the selectivity of olefin increases with an O/P value of 6.2.The hydrophilicity of the catalyst surface inhibited the secondary hydrogenation and promoted the chain growth,and the selectivity of linear α-olefin increased to 77.9%.(2)Based on the Fe3O4/MAG catalyst,the influence of different Fe3O4 particle size loading MAG on the distribution of CO hydrogenation products was investigated.The results showed that with the decrease of Fe3O4 particle size,which inhibited the water-gas conversion reaction,and the consumption of H2 is less whichis due to the selectivity of CH4 decreased from 17.7%to 6.6%,and the selectivity of CO2 decreased from 59.1%to 48.2%.The smaller particle size is easier to form metal clusters,and the proton-electron transfer between the carrier is easier,which inhibited the C-C coupling effect.The larger particle size enhanced the adsorption of CO and promoted the chain growth,so the selectivity of α-olefins rised from 63.5%to 77.9%.(3)Based on the Fe3O4/MAG catalyst,the role of the solvent selected for the preparation of the catalyst was explored.Through the comparison of water and ethanol,the results show that when ethanol is used as the dispersant,it can produce groups that are conducive to chain growth in the reaction process.The selectivity of olefin is higher,but its CO conversion rate is lower.