Fe2O3晶型对Fe基催化剂的CO2加氢性能影响

以共沉淀法制备FeAl母体,采用浸渍法添加Zn、K和Cu助剂制成催化剂,利用低温N2物理吸附、XRD、H2-TPR等手段对FeAl母体和催化剂进行表征,并用固定床反应器考察它们的CO₂加氢反应性能。XRD结果表明,加入Al助剂、并采用无水乙醇洗涤沉淀能促进酌-Fe₂O₃晶相生成,其中,Al₂O₃/Fe₂O₃质量比为10%的母体具有最强的酌-Fe₂O₃衍射峰;加入Al使得母体中的a-Fe₂O₃晶粒粒径变小,引起比表面积明显增大;浸渍助剂过程没有改变上述两种效应。母体比表面积增大提高了助剂Cu的分散度,促进了催化剂还原,但酌-Fe₂O₃晶相的生成才是催化剂的CO₂加氢反应活性被提高的主要原因。

Influence of Fe2 O3 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.