MgFeMn-HTLcs的制备、改性及其CO加氢性能

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

采用沉淀-水热法制备了系列不同Mg/Fe/Mn配比的Mg Fe Mn-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Mg O,Mg-Fe-Mn样品生成Mg_2Mn O_4、Mg O和Mg Fe_2O_4物相;反应后主要为Mg CO_3和Fe CO_3混合物相,伴随Fe O-Mn O和Fex Cy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Fe_2O_3到Fe_3O_4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,C_2~=C_4~=质量分数为43.03%。

A series of Mg Fe Mn-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 Mg Fe Mn-HTLcs precursors had typical layered structures of hydrotalcite and reduced crystallinity by Mn addition. After calcination, Mg O was only detected from Mg-Fe precursors whereas Mg2 MnO4, Mg O and Mg Fe2O4 were coexisted from Mg-Fe-Mn precursors. After CO hydrogenation, main phases were Mg CO3 and Fe CO3, accompanied by formation of Fe O-Mn O and little Fex Cy. Mn addition further promoted Fe dispersion and increased reduction from Fe2 O3 to Fe3 O4, compared to those of K/Mg-Fe catalysts. With Mn increase and its electron donating effect, binding energies of Fe2p 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/3 Mg-1 Fe-2 Mn catalyst.