Influence of Fe₂O₃ crystal phase on the performance of Fe-based catalysts for CO₂ hydrogenation

FeAl precursors (remarked as P) were prepared by co-precipitation method. Then they were impregnated with promoter Zn, K and Cu into ZnKCu/FeAl catalysts (remarked as C). The precursors and catalysts were characterized by low temperature N₂ adsorption, XRD and H2-TPR. CO₂ hydrogenation over these catalysts was investigated in a fixed-bed reactor. With the addition of Al, the specific surface area of FeAl precursors and ZnKCu/FeAl catalysts was increased relative to that of Al-free samples. On the contrary, the crystallite size of a-Fe₂O₃ was decreased by the added Al. The dispersed degree of Cu was raised in the catalysts containing Al. It is benefit for the reduction of ZnKCu/FeAl catalysts. However, the specific surface area and a -Fe₂O₃ crystallite size of P-10 and C-10, in which the Al2O3/Fe₂O₃ mass ratio is 10%, were similar to those of P-5 and C-5 with 5% Al 2O3/Fe₂O₃ mass ratio, respectively. The phenomena were resulted from the strong g-Fe₂O₃ phase in P-10 and C-10. It was evidenced that g-Fe₂O₃ was formed only in the case of Fe and Al were co-precipitated, and the precipitate was washed by anhydrous ethanol in this study. The catalyst with strong g-Fe₂O₃ phase was more active in CO₂ hydrogenation than the catalysts with none or weak g-Fe₂O₃ phase. This correlation was supported by the comparison between two catalysts with the same Al content, but different Fe₂O₃ phases in them.