Preparation of modified MgFeMn-HTLcs and catalytic performance in CO hydrogenation

doi:10.11949/j.issn.0438-1157.20180019

Abstract

Abstract:

A series of MgFeMn-HTLcs (hydrotalcite-like compounds) precursors with different Mg/Fe/Mn molar ratios were prepared by coprecipitation-hydrothermal method, which were then calcined and modified with K impregnation to be used as catalysts for light olefin synthesis from CO hydrogenation. The catalysts were characterized by XRD, SEM, TG, N₂ adsorption-desorption, H₂-TPR and XPS techniques. The results showed that MgFeMn-HTLcs precursors had typical layered structures of hydrotalcite and reduced crystallinity by Mn addition. After calcination, MgO was only detected from Mg-Fe precursors whereas Mg₂MnO₄, MgO and MgFe₂O₄ were co-existed from Mg-Fe-Mn precursors. After CO hydrogenation, main phases were MgCO₃ and FeCO₃, accompanied by formation of FeO-MnO and little Fe_xC_y. Mn addition further promoted Fe dispersion and increased reduction from Fe₂O₃ to Fe₃O₄, compared to those of K/Mg-Fe catalysts. With Mn increase and its electron donating effect, binding energies of Fe 2p were shifted to lower values. In CO hydrogenation, all prepared K/Mg-Fe-Mn catalysts showed high activity and C₂⁼-C₄⁼ selectivity. O/P value of 5.20 and C₂⁼-C₄⁼ fraction of 43.03% were achieved with low methane selectivity over K/3Mg-1Fe-2Mn catalyst.

Key words: Fischer-Tropsch synthesis, precursors, catalyst, hydrocarbon distribution, light olefins, selectivity

摘要：

采用沉淀-水热法制备了系列不同Mg/Fe/Mn配比的MgFeMn-HTLcs类水滑石前体，经焙烧、浸渍法K改性用于CO加氢制烯烃反应。采用XRD、SEM、TG、N₂吸附-脱附、H₂-TPR、XPS等手段对催化剂进行了表征。结果表明，制备的Mg-Fe-Mn前体均具有类水滑石层状结构，Mn的添加使结晶度下降；焙烧后，Mg-Fe样品主要生成MgO，Mg-Fe-Mn样品生成Mg₂MnO₄、MgO和MgFe₂O₄物相；反应后主要为MgCO₃和FeCO₃混合物相，伴随FeO-MnO和Fe_xC_y的生成；与K/Mg-Fe样品相比，Mn的加入进一步促进了Fe的分散，使得Fe₂O₃到Fe₃O₄还原度增加，其供电子效应促使Fe电子结合能向低偏移。在CO加氢反应中，K/Mg-Fe-Mn催化剂均表现出较高的反应活性和烯烃选择性。其中，K/3Mg-1Fe-2Mn催化剂的效果较好，CH₄含量较低，O/P值达5.20，C₂⁼～C₄⁼质量分数为43.03%。

关键词: 费-托合成, 前体, 催化剂, 烃分布, 低碳烯烃, 选择性

CLC Number:

O643

ZHANG Jianli, WANG Xu, MA Liping, YU Xufei, MA Qingxiang, FAN Subing, ZHAO Tiansheng. Preparation of modified MgFeMn-HTLcs and catalytic performance in CO hydrogenation[J]. CIESC Journal, 2018, 69(5): 2073-2080.

张建利, 王旭, 马丽萍, 于旭飞, 马清祥, 范素兵, 赵天生. MgFeMn-HTLcs的制备、改性及其CO加氢性能[J]. 化工学报, 2018, 69(5): 2073-2080.

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