合成气直接转化制芳烃化合物的双金属分子筛催化剂研究

Direct synthesis of aromatics from syngas can greatly raise the market competitiveness of the coal-to-aromatics project in China for its short process flow. In this project, a bimetallic Fe-Mo/HZSM-5 zeolite-based catalyst is designed and will be prepared with the aim of improving the selectivity to total aromatics. Over the catalyst, it is expected that the transition state species of hydrocarbons formed at Fe active sites from the syngas can move to Mo active sites and the Brønsted acid sites rapidly, and then be dehydrogenated and aromatized, avoiding the hydrogenation of methylene into methane and their excessive chain propagation. To explore and establish a suitable method and an appropriate procedure for catalyst preparation and catalyst activation, respectively, several methods for introduction of Fe and Mo species into the HZSM-5 and several procedures for their activation are going to be investigated. In detail, the morphology, composition and crystal type of Fe and Mo species in fresh and spent samples will be carefully characterized and their variations in the activation and reaction periods will be illustrated. Furthermore, the catalytic performances of prepared catalysts will be systematically investigated at varied reaction conditions, including the reaction temperature, reaction pressure, the ratio of CO and H2. Combination of various characterization technologies and special experimental means, the effects of structure characteristics of HZSM-5 zeolite, including the Si/Al ratio, the size of zeolite crystals and pore structure, on the location, morphology of Fe, Mo species on the zeolite and the catalytic performance of catalyst will be studied. Specially, the relationship between the detailed locations of Fe, Mo active sites on zeolite and the catalyst activity, aromatic types and distribution will be clarified for understanding of the aromatics’ formation mechanism in the reaction. Via studying of above mentioned concerns, the key technology for improving both distribution and selectivity of aromatics is expected to be achieved, providing a fundamental basis for further design and improvement of catalyst and promoting the development of C1 chemistry in both fundamental and practical fields.

合成气（CO+H2）直接转化制芳烃因其工艺流程短，可显著增加煤制芳烃的市场竞争力。为了提高芳烃选择性，本项目拟设计一种以HZSM-5分子筛为载体负载铁、钼组分的新型双金属催化剂，用于促进合成气在铁活性位上生成的烃类过渡态中间体快速地向钼活性位及分子筛酸位迁移完成脱氢芳构化，抑制甲烷化和过度链增长反应，从而提高芳烃选择性。通过研究铁、钼物种在分子筛上的引入方式和活化方法对活性组分的结构、相态在活化及反应过程中的变化规律，建立适宜的催化剂制备和活化方法，并评价催化剂在不同反应条件下的催化性能。运用多种表征技术和实验设计方案，阐明分子筛的结构特征及铁、钼活性物种在分子筛上的落位差异与CO转化、生成芳烃的类型和分布间的构效关系，明确合成气形成芳烃的反应机制。依托本项目的实施可为进一步设计和改良催化剂来改善芳烃分布、提高芳烃选择性提供理论基础，同时将促进C1化学基础及应用研究领域的发展。

将合成气（CO/CO2/H2）直接转化为芳烃化合物能够有效促进我国对煤炭、石油、天然气和生物质资源合理化工利用，提供一条芳烃生产路线，补充传统的以石油为基础的芳烃市场。本项目通过费托路线将铁基催化剂和HZSM-5分子筛复合构成多功能催化剂，有效实现了合成气向芳烃的转化。研究过程中，首先针对铁基费托催化剂对合成气催化转化进行了基础性的研究，考察了载体和助剂（K、Na和S）对铁基催化剂性能的共同作用，阐述了影响反应性能的关键因素，并通过改变还原气氛、反应温度以及反应压力进一步考察了评价条件对催化剂性能的影响；深入研究了Ag助剂提升FeMn催化剂性能的作用机制。以此为基础，构筑了FeMn-HZSM-5和Na/Fe-HZSM-5两类催化体系分别用CO和CO2催化加氢制备芳烃的研究，考察了反应温度、压力、空速、氢碳比、分子筛的硅铝比以及HZSM-5分子筛与Fe基催化剂的混合质量比等因素对催化活性、总烃中芳烃选择性和芳烃间产物分布的影响。在这些催化体系上，所获得的液相芳烃选择性可达95%以上，CO转化率可调的活性结果。通过大量的催化剂表征和有关DFT计算对催化过程和机理进行了深刻认识。通过该项目的研究，可为进一步设计和改良催化剂来改善芳烃分布、提高芳烃选择性提供理论基础。