碳基纳米笼限阈费托合成高选择性制汽油的新型催化剂研究

This NSFC application mainly focuses on the controllable construction, catalytic performance and regulation mechanism of new Fischer-Tropsch (F-T) catalysts confined in carbon-based nanocages towards selective synthesis of liquid fuel from syngas. The catalysts can be conveniently constructed by confining iron- or cobalt-based species into the nanocages with our self-developed vacuum-filling approach. The carbon-based nanocages own many advantages as the platform for confined F-T catalyst, such as hierarchical structure with confinement effect of nanoscale cavity, molecule sieving effect of the micropores through nanocage wall, adjustable electronic structures by doping, and coordination and anchoring effect of hetero atom for catalytic active species. The catalytic performances and reaction kinetics of the so-constructed catalysts for F-T synthesis from syngas to gasoline will be systematically investigated, especially on the effects of nanoscale cavity, micropores through nanocage wall, wall thickness, electronic structures of the nanocages, and situation of catalytic active species. The correlations between the F-T catalytic performance and the composition and structures of the confined catalysts will be studied in depth. The interactions between the nanocages and the catalytic active species are also investigated. Special attention will be paid on the mechanisms about carbon chain elongation and regulation, in comparison with the supported F-T catalysts outside the nanocages. It is highly expected that the two key factors, confinement effect of nanoscale cavity and molecule sieving effect of the micropores through nanocage wall, are beneficial to breaking through the limitation of Anderson-Schulz-Flory distributions. By this project, these findings should be helpful to direct the design and development of the novel carbon-based nanocage confined F-T catalysts with excellent performance from syngas to gasoline. In addition, the new confined F-T catalysts with self-owned intellectual property rights could be produced along this project towards high selectivity to the goal product.

本项目拟以申请人前期发展的形貌、结构独特的介观结构碳基纳米笼为载体，利用其纳米级空腔具有限阈作用、笼壁上微孔对分子具有筛分作用、电子结构易于掺杂调控、杂原子对催化活性组分具有锚定作用等有利因素，采用自主发展的真空-填充方法，可控构建碳基纳米笼限阈的Fe基、Co基纳米复合催化剂。系统研究此类新型限阈催化剂的费托合成制汽油的催化性能和催化反应动力学，着重研究碳基纳米笼的纳米级空腔、笼壁上微孔尺寸、笼壁厚度、掺杂等因素对催化性能的影响，确立催化性能与催化剂成分、结构之间的关系。通过与负载型催化剂对比，认识其限阈效应和微孔的筛分作用规律、碳链增长机理和调控机制，揭示突破Anderson-Schulz-Flory产物分布限制的关键因素及其催化作用基础，为设计和开发先进的碳基纳米笼限阈的费托合成制汽油的新型纳米催化剂提供科学依据，并优化出高性能的碳基纳米笼限阈复合催化剂，实现目标产物的高选择性制备。

为应对石油资源日益枯竭、大规模使用化石燃料带来的严重环境问题等，发展非石油来源液体燃料及高附加值化学品的费托合成技术对我国更具经济和战略意义。费托合成产物分布一般遵循经典的Anderson-Schulz-Flory(ASF)产物分布规律，难以高选择性地获得目标产物，如燃油。本项目在执行过程中很好地完成了既定的研究目标。主要进展包括：(1) 可控制备出新型具有分级结构和笼壁富含微孔的非掺杂、单掺杂或共掺杂的碳基纳米笼，其纳米级空腔尺寸、笼壁厚度、纳米笼塌陷程度、比表面、孔分布、微-介-大孔体积、石墨化程度、掺杂元素含量和存在状态等参数可有效调控；开发了MgO@ZnO复合模板法和CO2活化扩孔法来进一步增加纳米笼笼壁的微孔尺寸和数量，采用在纳米笼表面再沉积碳层的方法来减少纳米笼笼壁的微孔尺寸和数量；为构建具有独特功能的限域催化剂和其他功能材料提供契机。(2) 采用真空-填充+冷冻干燥+酸洗方法构建出了系列碳基纳米笼限阈的Fe基、Co基、Ru基纳米复合催化剂。(3) 限阈催化剂的产物分布突破ASF产物分布规则，获得了比负载型催化剂更高汽柴油组分的选择性和低的甲烷选择性，C5-C20组分的选择性可达78%，其催化活性和抗烧结稳定性也显著优于负载型催化剂；适中的笼壁厚度和微孔尺寸可以得到优化的FT合成的催化活性、产物选择性，可归因于CNC纳米笼空腔的限阈作用和笼壁微孔通道的筛分效应使产物分布突破ASF产物分布限制，有利于获得汽柴油组分，笼壁微孔通道限制了费托合成过程中原位形成的羰基铁的传质，使限阈型催化剂的抗烧结性能显著优于负载型催化剂。(4) 首次揭示出在费托合成反应过程中碳化铁颗粒烧结的羰基铁介导的类奥斯瓦尔德熟化机制，以此为指导，通过控制氮掺杂碳纳米笼的氮掺杂量，可控地设计和制备出抗烧结催化剂。