Yang Shuo, Li Minzhe, Nawaz Muhammad Asif, Song Guiyao, Xiao Wentao, Wang Zihao, Liu Dianhua
State Key Lab of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China.
ACS Omega. 2020 May 12;5(20):11701-11709. doi: 10.1021/acsomega.0c01007. eCollection 2020 May 26.
The demand for aromatics, especially benzene, toluene, and xylene, has been increased in recent years as the crucial feedstocks of coatings and pharmaceutical industry. In this work, a modified Fischer-Tropsch synthesis (FTS) catalyst FeNaMg was fabricated via a sol-precipitation method and integrated with an HZSM-5 aromatization catalyst for the aromatics synthesis from syngas by a one-step process. Syngas was first converted to lower olefins as intermediates on the active component of the FeNaMg catalyst followed by aromatization on zeolite. Different characterization approaches, such as BET, XRD, XPS, hydrogen temperature-programmed reduction, temperature-programmed desorption of CO, TG, and SEM, revealed that Mg efficiently optimized physicochemical properties of the Fe-based catalyst by generating a MgFeO spinel structure. Further investigation demonstrated that the MgFeO spinel structure could increase the syngas adsorption area, facilitating the reduction and carburization of the Fe phase, while Mg decreased CO selectivity (31.26 to21%) by restraining the water-gas shift reaction and improved the utilization efficiency of carbon. At the same time, alkali metal Na changed the surface electronic environment of the FTS catalyst to enhance CO adsorption as an electronic promoter, which suppressed methane formation by restraining over hydrogenation. Therefore, the synergism that existed between Mg and Na during the reaction escalated the CO conversion and aromatics selectivity to 96.19 and 51.38%, respectively.
近年来，作为涂料和制药行业的关键原料，对芳烃尤其是苯、甲苯和二甲苯的需求不断增加。在本工作中，通过溶胶沉淀法制备了一种改性费托合成（FTS）催化剂FeNaMg，并将其与HZSM-5芳构化催化剂集成，用于通过一步法由合成气合成芳烃。合成气首先在FeNaMg催化剂的活性组分上转化为低级烯烃作为中间体，然后在沸石上进行芳构化。不同的表征方法，如BET、XRD、XPS、氢气程序升温还原、CO程序升温脱附、TG和SEM，表明Mg通过生成MgFeO尖晶石结构有效地优化了铁基催化剂的物理化学性质。进一步研究表明，MgFeO尖晶石结构可以增加合成气吸附面积，促进Fe相的还原和渗碳，而Mg通过抑制水煤气变换反应降低了CO选择性（从31.26%降至21%），提高了碳的利用效率。同时，碱金属Na作为电子促进剂改变了FTS催化剂的表面电子环境，增强了CO吸附，通过抑制过度氢化抑制了甲烷的形成。因此，反应过程中Mg和Na之间存在的协同作用将CO转化率和芳烃选择性分别提高到了96.19%和51.38%。
