新型Fe基费托合成制低碳烯烃催化剂的精细调控与机理研究
发布时间：2018-08-06 13:59
【摘要】：低碳烯烃(C2=-C4=)是基础且重要的有机化工原料,工业上主要通过石脑油裂解或烷烃脱氢获得。对于我国"富煤、贫油、少气"的能源结构而言,开发基于煤、生物质等来源的合成气(低H2/CO比)经费托合成直接制备低碳烯烃(FTO)工艺,对均衡合理利用我国资源、确保国家能源安全具有十分重要的战略意义。近年来,负载型Fe基催化剂因能直接转化煤、生物质等来源的合成气高选择性制备低碳烯烃,且兼具成本低廉、强度高、抗中毒性强等优点,而备受关注。本文针对目前Fe基FTO催化剂中Fe物种与助剂之间的不均匀分布、表界面结构特性与催化机理不明晰等问题,采用KMnO4或K2FeO4氧化修饰CNTs制备Fe基复合物纳米催化剂,通过调变热处理方式来调变金属与助剂之间的作用方式,实现了微观尺度上铁物种与助剂之间的均匀混合,建立了催化剂表界面结构与FTO性能之间的构-效关系。此外,结合DFT计算与稳态同位素瞬变动力学分析(SSITKA),提出了 Fe基催化剂上新的费托合成机理。(1)基于KMnO4氧化修饰CNTs获取的MnK-CNTs复合物纳米材料随温度、气氛变化表现出独特的结构转变性质,即随热处理温度的升高,CNTs表面的层状MnO2可自发转变为球形纳米颗粒,且在一定还原条件下,可保证锰的晶相由MnO2完全转变为MnO,制备了一种新型Fe基复合物纳米催化剂(Fe/MnK-CNTs)。相较于传统共浸渍法制备的FeMnK/CNTs催化剂,该类新型催化剂不仅具有较小粒径和分散均匀的铁纳米颗粒、微观尺度上均匀混合的铁物种与助剂,而且金属-载体相互作用较弱、载体表面缺陷较多。(2)新型Fe/MnK-CNTs催化剂相较于FeMnK/CNTs催化剂具有较短的诱导期以及较高的反应活性、C2=-C4=选择性和C2-C4烃类中烯烃/烷烃之比,且反应后的催化剂中铁颗粒仍均匀分散,未发生明显的团聚现象,并生成更多的活性相x-Fe5C2。这表明利用MnK-CNTs复合物纳米材料随温度、气氛变化独特的结构转变性质是一种制备高效Fe基FTO催化剂的可行思路。(3)调变Fe/MnK-CNTs催化剂焙烧温度可以显著改变催化剂的微观形貌、金属-载体相互作用、载体表面缺陷、催化剂的碳化能力和稳定性等,发现当焙烧温度为220℃时,相应的C-220催化剂表现出较高的活性、C2=-C4=选择性和烯烃/烷烃之比等,且在较优反应条件(270℃、2.0MPa以及GHSV=30000mL·h-1·gcat-1)下可获得较高的FTY(337.2 μmolco·gFe-1·s-1)和51.3%C的C2=-C4=选择性。进一步研究了 Mn负载量对催化剂FTO性能的影响,发现提高Mn含量尽管有利于提高低碳烯烃选择性,但同时增加了催化剂还原和碳化的难度,延长了反应诱导期。此外,研究发现较低的碳化温度或较高的%,有利于催化剂活性相的生成。(4)基于K2FeO4和CNTs之间的氧化还原反应,一步法制备了新型Fe-K基催化剂FeK-OX。系统的催化剂结构与FTO性能表征结果表明:新型FeK-OX催化剂相较于传统共浸渍法制备的FeK-IM催化剂具有粒径较小且分布均匀的铁纳米颗粒、独特的金属与助剂接触方式、较多的载体表面缺陷等,因而表现出较高生成低碳烯烃的、稳定的比质量活性以及较短的诱导期。在此基础上,通过浸渍法进一步引入K助剂,可以显著提高催化剂的FTY,降低甲烷选择性。这预示着通过浸渍法向FeK-OX催化剂引入K助剂是一种有效的提高反应活性和抑制甲烷生成的方法。(5)考虑到费托合成反应路径的复杂性,发展了针对Fe基催化剂的多组分SSITKA方法,将分析方法拓展到Fe基催化剂上的C2-C6产物,从表面活性物种的测定、TOF、同位素分布曲线等方面对传统的SSITKA分析方法进行修正。结合基于SSITKA实验的动力学分析和DFT计算,辨认出SSITKA测试条件下铁基催化剂上CO较优的活化路径以及速率决定步骤等。(6)结合上述研究结果提出了 Fe基FTO催化剂主要活性相x-Fe5C2上可能的反应机理:碳化铁表面上CO活化产生的CHx与表面C原子或其加氢物种CHy结合发生C-C偶联反应,其产生的碳空穴有利于CO活化,恢复完美的碳化铁表面,然后遵循上述相似的C-C偶联机理实现链增长,且最终形成的烃类产物端位C原子来自于原始碳化铁表面上的C原子。
[Abstract]:Low carbon olefin (C2=-C4=) is a basic and important organic chemical raw material. It is obtained by naphtha cracking or dehydrogenation of alkanes in industry. For the energy structure of "rich coal, poor oil and less gas" in our country, the process of preparing low carbon olefin (FTO) based on coal, biomass and other sources of synthetic gas (low H2/CO ratio) is developed. Using our resources to ensure national energy security is of great strategic significance. In recent years, the supported Fe based catalysts have attracted much attention because they can directly convert coal, biomass and other sources of synthetic gas to produce low carbon olefins with high selectivity, which has the advantages of low cost, high strength and strong toxic resistance. This paper is aimed at the current Fe based FTO. The uneven distribution of Fe species and auxiliaries in the chemical agent, the structure characteristics of the surface interface and the catalytic mechanism are not clear. The nano catalyst of Fe based complex is prepared by KMnO4 or K2FeO4 oxidation modification, and the action formula between metals and additives is adjusted by the adjustment heat treatment, and the iron species and the auxiliary agent in the micro scale are realized. The structure effect relationship between the surface structure of the catalyst and the properties of FTO was established. In addition, the new Fischer Tropsch synthesis mechanism on the Fe based catalyst was proposed by DFT calculation and steady-state isotope transient dynamics analysis (SSITKA). (1) the MnK-CNTs composite nanomaterials obtained by KMnO4 oxidation modified CNTs with the temperature and atmosphere change table With the increase of heat treatment temperature, the layered MnO2 on the surface of CNTs can be transformed into spherical nanoparticles spontaneously, and under certain reduction conditions, the crystalline phase of manganese can be completely transformed from MnO2 to MnO, and a new Fe based nanocompound (Fe/MnK-CNTs) is prepared. Compared with the traditional co impregnation method, it is prepared. FeMnK/CNTs catalyst, the new type of catalyst not only has small particle size and dispersed uniform iron nanoparticles, but also has a uniform mixing of iron species and auxiliaries on the micro scale, but the interaction of metal carrier is weak, and the surface defects of the carrier are more. (2) the new type of Fe/MnK-CNTs catalyst has a shorter induction period than the FeMnK/CNTs catalyst. And higher reactive activity, C2=-C4= selectivity and the ratio of olefin / alkanes in C2-C4 hydrocarbons, and the iron particles are still dispersed evenly in the catalyst after reaction, and there is no obvious agglomeration, and more active phase x-Fe5C2. is generated. This indicates that the unique structure transformation properties of the MnK-CNTs complex nano material with the temperature change are a kind of unique structure transformation properties. The feasible idea of preparing high efficiency Fe based FTO catalyst. (3) the temperature of the modified Fe/MnK-CNTs catalyst can significantly change the micromorphology of the catalyst, the metal carrier interaction, the surface defect of the carrier, the carbonization ability and stability of the catalyst, and found that the corresponding C-220 catalyst showed higher activity when the calcination temperature was 220, C2= -C4= selectivity and the ratio of alkene / alkane, and higher FTY (337.2 molco. GFe-1. S-1) and 51.3%C C2=-C4= selectivity under the better reaction conditions (270, 2.0MPa and GHSV=30000mL. H-1. Gcat-1). Further study the effect of the amount of Mn load on the performance of the catalyst. Olefin selectivity, but also increased the difficulty of the catalyst reduction and carbonization, extended the reaction induction period. In addition, the study found that lower carbonation temperature or higher%, is beneficial to the generation of active phase of the catalyst. (4) based on the redox reaction between K2FeO4 and CNTs, a new Fe-K based catalyst FeK-OX. system catalyst was prepared by one step method. The characterization results of the structure and FTO show that the FeK-IM catalyst prepared by the new FeK-OX catalyst has smaller size and uniform distribution of iron nanoparticles than the traditional co impregnation method, the unique contact mode of metal and auxiliaries, more surface defects of the carrier and so on, thus showing a stable ratio of quality to Gao Shengcheng's low carbon olefin. On this basis, further introduction of K additives by impregnation can significantly increase the FTY of the catalyst and reduce the selectivity of methane. This indicates that the introduction of K additive to the FeK-OX catalyst by impregnation is an effective way to improve the reaction activity and inhibit the formation of methane. (5) the complex reaction path of the Fischer Tropsch synthesis is taken into account. The multi component SSITKA method for Fe based catalysts was developed. The analytical method was extended to the C2-C6 products on the Fe based catalyst. The traditional SSITKA analysis methods were corrected from the determination of the surface active species, the TOF, the isotopic distribution curve and so on. In combination with the kinetic analysis based on the SSITKA experiment and the DFT calculation, the SSITKA measurement was identified. The better activation path of CO and the rate determination step on the iron base catalyst. (6) the possible reaction mechanism on the main active phase x-Fe5C2 of the Fe based FTO catalyst was proposed in combination with the above results: the CHx produced by CO activation on the surface of the iron carbide and the C-C coupling reaction of the surface C atom or the CHy binding of the hydrogenated species were produced by the C-C coupling reaction. The carbon vacancies are beneficial to CO activation, restore the perfect surface of the iron carbide, and follow the similar C-C coupling mechanism to achieve chain growth, and the end C atoms of the final hydrocarbon products are derived from the C atoms on the surface of the original iron carbide.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ426;TQ529.2
，
本文编号：2167945
[Abstract]:Low carbon olefin (C2=-C4=) is a basic and important organic chemical raw material. It is obtained by naphtha cracking or dehydrogenation of alkanes in industry. For the energy structure of "rich coal, poor oil and less gas" in our country, the process of preparing low carbon olefin (FTO) based on coal, biomass and other sources of synthetic gas (low H2/CO ratio) is developed. Using our resources to ensure national energy security is of great strategic significance. In recent years, the supported Fe based catalysts have attracted much attention because they can directly convert coal, biomass and other sources of synthetic gas to produce low carbon olefins with high selectivity, which has the advantages of low cost, high strength and strong toxic resistance. This paper is aimed at the current Fe based FTO. The uneven distribution of Fe species and auxiliaries in the chemical agent, the structure characteristics of the surface interface and the catalytic mechanism are not clear. The nano catalyst of Fe based complex is prepared by KMnO4 or K2FeO4 oxidation modification, and the action formula between metals and additives is adjusted by the adjustment heat treatment, and the iron species and the auxiliary agent in the micro scale are realized. The structure effect relationship between the surface structure of the catalyst and the properties of FTO was established. In addition, the new Fischer Tropsch synthesis mechanism on the Fe based catalyst was proposed by DFT calculation and steady-state isotope transient dynamics analysis (SSITKA). (1) the MnK-CNTs composite nanomaterials obtained by KMnO4 oxidation modified CNTs with the temperature and atmosphere change table With the increase of heat treatment temperature, the layered MnO2 on the surface of CNTs can be transformed into spherical nanoparticles spontaneously, and under certain reduction conditions, the crystalline phase of manganese can be completely transformed from MnO2 to MnO, and a new Fe based nanocompound (Fe/MnK-CNTs) is prepared. Compared with the traditional co impregnation method, it is prepared. FeMnK/CNTs catalyst, the new type of catalyst not only has small particle size and dispersed uniform iron nanoparticles, but also has a uniform mixing of iron species and auxiliaries on the micro scale, but the interaction of metal carrier is weak, and the surface defects of the carrier are more. (2) the new type of Fe/MnK-CNTs catalyst has a shorter induction period than the FeMnK/CNTs catalyst. And higher reactive activity, C2=-C4= selectivity and the ratio of olefin / alkanes in C2-C4 hydrocarbons, and the iron particles are still dispersed evenly in the catalyst after reaction, and there is no obvious agglomeration, and more active phase x-Fe5C2. is generated. This indicates that the unique structure transformation properties of the MnK-CNTs complex nano material with the temperature change are a kind of unique structure transformation properties. The feasible idea of preparing high efficiency Fe based FTO catalyst. (3) the temperature of the modified Fe/MnK-CNTs catalyst can significantly change the micromorphology of the catalyst, the metal carrier interaction, the surface defect of the carrier, the carbonization ability and stability of the catalyst, and found that the corresponding C-220 catalyst showed higher activity when the calcination temperature was 220, C2= -C4= selectivity and the ratio of alkene / alkane, and higher FTY (337.2 molco. GFe-1. S-1) and 51.3%C C2=-C4= selectivity under the better reaction conditions (270, 2.0MPa and GHSV=30000mL. H-1. Gcat-1). Further study the effect of the amount of Mn load on the performance of the catalyst. Olefin selectivity, but also increased the difficulty of the catalyst reduction and carbonization, extended the reaction induction period. In addition, the study found that lower carbonation temperature or higher%, is beneficial to the generation of active phase of the catalyst. (4) based on the redox reaction between K2FeO4 and CNTs, a new Fe-K based catalyst FeK-OX. system catalyst was prepared by one step method. The characterization results of the structure and FTO show that the FeK-IM catalyst prepared by the new FeK-OX catalyst has smaller size and uniform distribution of iron nanoparticles than the traditional co impregnation method, the unique contact mode of metal and auxiliaries, more surface defects of the carrier and so on, thus showing a stable ratio of quality to Gao Shengcheng's low carbon olefin. On this basis, further introduction of K additives by impregnation can significantly increase the FTY of the catalyst and reduce the selectivity of methane. This indicates that the introduction of K additive to the FeK-OX catalyst by impregnation is an effective way to improve the reaction activity and inhibit the formation of methane. (5) the complex reaction path of the Fischer Tropsch synthesis is taken into account. The multi component SSITKA method for Fe based catalysts was developed. The analytical method was extended to the C2-C6 products on the Fe based catalyst. The traditional SSITKA analysis methods were corrected from the determination of the surface active species, the TOF, the isotopic distribution curve and so on. In combination with the kinetic analysis based on the SSITKA experiment and the DFT calculation, the SSITKA measurement was identified. The better activation path of CO and the rate determination step on the iron base catalyst. (6) the possible reaction mechanism on the main active phase x-Fe5C2 of the Fe based FTO catalyst was proposed in combination with the above results: the CHx produced by CO activation on the surface of the iron carbide and the C-C coupling reaction of the surface C atom or the CHy binding of the hydrogenated species were produced by the C-C coupling reaction. The carbon vacancies are beneficial to CO activation, restore the perfect surface of the iron carbide, and follow the similar C-C coupling mechanism to achieve chain growth, and the end C atoms of the final hydrocarbon products are derived from the C atoms on the surface of the original iron carbide.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ426;TQ529.2
，
本文编号：2167945
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