3DOM-MgFexAl2-xO4催化剂可控制备及其乙苯与CO2氧化脱氢性能研究

Supported iron oxide-based catalyst is the active catalyst for ethylbenzene dehydrogenation to styrene with CO2. However, the fast deactivation due to the coke deposition and the sintering of the active Fe species at the high reaction temperature（≥ 550℃） still restrain the its utilization. In our previous study, a nano-catalyst of MgFe0.1Al1.9O4 was prepared for ethylbenzene dehydrogenation with CO2. The iron species in the spinel possesses strong capacity to inhibit sintering, but it shows low catalytic stability due to the coke deposition. Based on this work, herein we propose the synthesis of a novel type of MgFexAl2-xO4(x=0.1, 0.3, 0.5) catalyst with three-dimensionally ordered macroporous (3DOM) structure, which contributes to the depressing of coke deposition. The aim of the work is to develop a stable industrial catalyst for this reaction. 3DOM-MgFexAl2-xO4 will be synthesized by colloidal crystal method: poly-methyl methacrylate (PMMA) and metal nitrates serve as the template and starting materials, respectively. The 3DOM catalyst with different pore size, wall thickness and specific surface area will be prepared through the control of the particle size of PMMA microspheres. The segregation phenomenon of the metal compositions during the synthesis will be restrained through some experimental methods, such as adding complexing agent into the metal oxide precursor, decreasing the O2 content in the calcining atmosphere to remove PMMA, etc. The physico-chemical properties of the catalysts will be characterized, and its catalytic performance for ethylbenzene dehydrogenation with CO2 will be investigated. The influences of the preparation parameters on the properties of the catalysts, such as the phase structure, pore size, specific surface area, and the valence and reducibility of Fe in spinels, will be discussed. The relationship between structure and catalytic performance of the 3DOM-MgFexAl2-xO4 will be exposited. The results obtained in this work will be important for both synthesis and catalytic application of 3DOM composite oxides.

负载型Fe基催化剂对乙苯与CO2氧化脱氢制苯乙烯具有良好的反应活性，但在较高反应温度（≥550℃）下极易因活性组分烧结、积碳而失活。将Fe物种掺杂进入复合氧化物骨架内可以抑制其烧结，但积碳问题仍然存在。在对Fe3+掺杂的MgAl2O4尖晶石催化剂研究基础上，本项目提出制备具有三维有序大孔（3DOM）结构的MgFexAl2-xO4催化剂的设想，在保持活性组分抗烧结能力的同时，提高积碳前驱体扩散速率，降低积碳。3DOM催化剂拟采用胶体晶体法制备，通过调变模板微球尺寸控制3DOM孔道性质，采用添加络合剂、多次浸渍和调控焙烧工艺等方法控制无机骨架前驱物的反应行为、骨架中/微孔结构以及催化剂机械强度。研究制备工艺参数对催化剂孔道结构及催化性质的影响。本项目研究对丰富3DOM材料制备化学、研发乙苯-CO2脱氢反应新型催化剂具有学术意义和应用价值。

本项目采用无皂乳液聚合法合成了的聚甲基丙烯酸甲酯 (PMMA) 微球, 并以此为模板制备了具有三维有序大孔 (3DOM) 结构的MgFe0.1Al1.9O4尖晶石催化剂, 研究了催化剂3DOM结构对其在乙苯与CO2氧化脱氢生成苯乙烯反应中稳定性的影响。 结果表明， 合成的3DOM MgFe0.1Al1.9O4 催化剂具有三维有序大孔结构, 其大孔孔径为230 nm, 孔壁平均厚度为 60 nm， 其中大部分Fe物种以同晶取代的方式进入到尖晶石骨架中。该催化剂在乙苯与CO2氧化脱氢反应中表现良好的催化活性和稳定性。通过与具有相同化学组成的nano MgFe0.1Al1.9O4催化剂对比研究发现，3DOM MgFe0.1Al1.9O4畅通的孔道结构十分有利于反应积碳前驱物的外扩散, 对提高催化剂的稳定性具有重要作用。此研究结果为乙苯与CO2氧化脱氢反应催化剂的研发提供了一种新型催化材料, 具有重要意义。