Research On Catalysts For Carbon Dioxide Hydrogenation To Produce Light Olefins

As the basic raw materials in the chemical industry,light olefins mostly come from petroleum cracking and highly depend on foreign sources.The shortage of petroleum resources and high emissions of CO2 have severely restricted the rapid development of China’s chemical industry.Under the dual pressure of environment and energy,there is an urgent demand to find a non-petroleum route for olefin production process.Nevertheless,utilizing CO2 as a carbon source through thermal catalytic hydrogenating to get light olefins meets the requirements of energy development strategy in China,which are clean,low-carbon,and efficient.Catalysts play an important role in the conversion and utilization of CO2.Based on the FT reaction pathway with CO as an intermediate,and relying on the characteristics of low cost of Fe-based catalysts,strong capabilities of reversed water gas and FT reaction capabilities,this paper designs and studies the high selectivity production of Fe-based catalysts with special morphology structure while maintaining high activity.First,Fe3O4 microsphere catalyst was prepared by hydrothermal synthesis method.The crystal phase composition and morphology structure were determined by XRD test and SEM scanning analysis.The production of hydrothermal synthesis is Fe3O4 microspheres with uniform distribution and without obvious agglomeration.The N2 adsorption-desorption test of the catalyst showed that Fe3O4 microspheres have non-porous structure,which can eliminate the influence of pores and diffusion effects,compared with the traditional FT catalysts.The performance evaluation of four different iron-based catalysts under the same reaction conditions showed that the Fe3O4 microsphere catalyst has the optimal product distribution and stable and excellent activity.Then,in order to alleviate the fierce competition of the methanation reaction in the FTS,Fe3O4 microspheres were used as the support,different kinds of promoters were added to control the product distribution.After the addition of alkali metal Rb promoter,the methane selectivity was significantly reduced,it’s worth noting that the selectivity of light olefins increased by nearly twice.The XRD and XPS tests analysis of the catalyst after offline reduction showed the strong interaction between the Rb promoter and Fe species in the catalyst,which can obviously promote the carburization of the catalyst during the reduction process to form iron-carbon compounds with FT activity.At the same time,the results of CO2-TPD showed that the addition of Rb promoter enhanced the adsorption strength of CO2,reduced the H/C ratio on the catalyst surface and was beneficial for the generation of light olefins.After optimizing the loading ratio and process conditions,the results indicate that when 3 wt.%Rb/Fe3O4 at the condition of 300℃,0.5 MPa,H2/CO2=3,the selectivity of light olefins is the highest,reaching 47.44%,the conversion rate is 39.74%,the selectivity of all olefins is as high as 72.33%,which successfully realized the efficient conversion of CO2 to light olefins.The research of this subject can provide new ideas for the design and synthesis of high-efficiency catalysts for the hydrogenation of CO2 to high-value chemicals.