Study On Co Hydrogenation To Light Olefins Using Iron-based Catalysts

With the decreasing of global oil reserves and the shortage of olefins in the energy market,the conversion of carbon monoxide into hydrocarbons,especially low carbon olefins,has always been the focus of attention from around the world.As an oil-poor country,China can get rid of the dependence on petroleum import and adjust the energy structure,by using Fischer-Tropsch synthesis（FTS）reaction to convert alternative energy into fuels,such as light olefins.At present,iron-based catalysts are considered as the most suitable catalysts for the synthesis of low carbon olefins（C₂⁼-C₄⁼）in FTS reactions.Herein,the paper mainly focused on the effect of special structure of Fe Foam and promoters loaded on inert support on Fischer-Tropsch active phase,and provide theoretical basis for the development of efficient FT catalyst for light olefins.Fe Foam catalysts with high olefin selectivity,stability and thermal conductivity were prepared by impregnation method.It is beneficial to product diffusion and preventing secondary hydrogenation reaction,because Fe Foam has a larger pore size（392nm）than the traditional iron-based catalyst.In the conditions closed to industrial reaction（350℃and 1MPa）,we found that the olefin selectivity of Fe Foam with alkali metal promoter is 1.9 times as much as that of unsupported sample,and the O/P of Fe Foam with alkali metal promoter is 7 times as much as that of unsupported sample.In addition,KMn/Fe Foam catalyst realizes the high selectivity of olefin as 76.1%.Furthermore,the effect of Fe Foam’s microporous structure and promoters on catalytic activity and product distribution were characterized by MIP,XRD,XPS,TEM and SEM.We load promoters on Al₂O₃ and mix it with Fe₂O₃,studying the effect of promoters loaded on inert support on the FTS active phase and the distribution of FT products.In the same reduction and reaction conditions,the olefin selectivity of the catalysts with promoters was increased by 20%,and the light olefins selectivity of 10Mn/Al₂O₃+Fe₂O₃ is 51.3%.The results of XRD and XPS indicate that the electronic state of Fe atoms on the surface of the sample with promoters has changed and more C-poor phasesθ-Fe₃C were formed.In addition,the reduction and carbonization process of the catalysts were investigated by TPR and TPD characterization.Combined with the experimental data,it was confirmed that the synergy effect of the support and the promoter significantly facilitate the formation of active phase Fe₃C,which is in favor of the formation of light olefin.