Reaction Mechanism And Iron-Based Bifunctional Catalyst Design Of CO₂ Hydrogenation To Aromatics

Aromatics is the basic organic chemical raw materials for the production of bulk petrochemical products.It is widely used in the synthesis of organic industries,including dyes,plastics,synthetic resins,pesticides,pharmaceutical processing and other fields.The output and consumption of aromatics reflect the level of national economic development and the level of chemical industry.The method of preparing aromatics via CO₂ hydrogenation can not only reduce the excessive dependence of aromatics production on petroleum resources,but also contribute to the realization of the national strategic goals of‘carbon neutrality’and‘carbon peaking’.Therefore,Cu-modified Fe₃O₄ catalysts and chain-like ZSM-5 zeolites were prepared and used as bifunctional catalysts for single-step selective conversion of carbon dioxide to high value-added aromatics.The main work and results were as follows:1.Cu-modified Fe₃O₄ catalysts were prepared by solvothermal method,and the effect of different Cu modification ratios on CO₂ hydrogenation performance was study.The results showed that Cu promoter improved the adsorption capacity of Fe-based catalysts for CO₂,thereby increasing the C/H ratio on the surface of Fe-based catalysts,promoting carbon-carbon coupling,and shifting olefin products to high carbon number olefins.At the same time,Cu additives also promoted the activation and dissociation of H₂,and improved the conversion rate of CO₂.Further optimization of the reaction conditions resulted in a maximum C₅₊⁼selectivity of 45.2%at Cu/Fe of 2.76%,reaction temperature of 340℃,and space velocity of 2000 ml/（h·g）.Further coupling zeolites to form bifunctional catalysts,the results of the reaction of CO₂ hydrogenation to aromatics showed an increasing trend of aromatic selectivity with the increase of high carbon number olefins.By introducing Cu,the aromatic selectivity was improved by 11%to 30.3%compared to the unmodified condition.This suggested that high carbon number olefins were beneficial to aromatization at zeolites to obtain aromatic hydrocarbons.However,the distribution of aromatics was not affected by the modulation of olefin intermediates.2.A series of chain-like ZSM-5 zeolites with different acid densities and different length-diameter ratios was prepared by hydrothermal method and formed bifunctional catalysts with 3Cu-Fe₃O₄catalysts.The effects of acid density and length-to-diameter ratio of zeolites part on the selectivity and distribution of aromatic products was studied.Studies showed that the chain-like ZSM-5 with high acid density promoted the C-C coupling of the product,inhibited the generation of CH₄,and improved effectively the selectivity of aromatics and the space-time yield of light aromatics（benzene,toluene,xylene.BTX）.Adjusting length-to-diameter ratio of chain-like zeolites improved the relative proportion of toluene in BTX,thereby increasing the space-time yield of toluene which reached up to 3.2 mmol/(g _Fe×h).It was proved that the selectivity and distribution of aromatics were effectively adjusted by regulating the mass transfer process of olefin intermediates in zeolites.In addition,the too close proximity of bifunctional catalysts was not conducive to aromatics formation.