Studies On The Preparation Of Iron-based Catalysts And Their CO₂ Hydrogenation Performance

Carbon dioxide(CO2) is the final product of carbon or carbide oxide, which is one of the most abundant carbon resource. But in recent years, with the increasing emission, it damages to the human survival environment and the earth’s ecological system seriously. So it urgently need to transform CO2 to valuable commodity and make the waste to profit, which is important to environmental protection and the sustainable development of human society. CO2 hydrogenation to hydrocarbons is one of the most effective solutions to remit the environmental pollution and the shortage of current energy supply. Iron-based( Fe) catalyst, with good performance, has been largely applied in CO2 hydrogenation.This paper focuses on changing the preparation conditions and methods in order to acquire diverse catalyst precursors with different specific surface area and Fe2O3 phase structure. Then iron-based catalysts were prepared by impregnating Zn, K and Cu. The catalysts were evaluated in a fixed-bed reactor for CO2 hydrogenation and characterized by N2 physical adsorption, H2-TPR, XRD and XPS. Several results have been obtained as follows:The iron atoms in the dried precipitates exist in different phases depended on the drying temperature. It is amorphous in the sample dried at 80 °C. The strongest diffraction peaks of α-FeOOH are observed in the sample dried at 140 °C. α-FeOOH begins to dehydrate at 160 °C and α-Fe2O3 appears at 180 °C. All of α-FeOOH is transformed into α-Fe2O3 after calcination, but the crystallite size is influenced by drying temperature. The reactivity of ZnKCu/FeAl catalysts is increased firstly and then decreased with the elevation of drying temperature for CO2 hydrogenation. The catalyst originated from 140 °C dried Fe Al is the most active one among the studied catalysts.The crystallite diameter of iron-based catalysts is greatly decreased with the increasing of added Al contents, which is in favor of improving dispersity of the active components and promoters, and optimizing the surface structure of catalysts. Moreover, Al as structure promoter, can strengthen the interaction between Fe and Cu, which facilitated the reduction degree of catalysts and CO2 hydrogenation performance. XRD results show that Al can help γ-Fe2O3 phase generated, especially 10% Al2O3 can further raise the CO2 hydrogenation performance and C5+ selectivity.CO2 hydrogenation performance of catalyst is altered by different crystal phase structure. Calcination treatment causes the crystallite size of α-Fe2O3 increased, which is disadvantage to the dispersity of the active components and promoters, eventually lead to poor CO2 hydrogenation performance. By contrast, γ-Fe2O3 crystallite diameter is smaller, which is beneficial to uniform dispersion of active components, and can be reduced completely in low temperature. These can improve CO2 hydrogenation and C5+ selectivity.