铁/介孔氧化硅核壳颗粒的碳模板法合成及催化性能研究

The key technologies for forming lower olefins from synthesis gas are designation and fabrication of novel catalysts. In this application, a novel ferrous core-shell particle (Fe@SiO2) is proposed to be developed to catalyze the reaction. The novel synthetic route, preparing this nano-composite catalyst from C-template will be carried out: ferrous core encapsulated with Si/C shell will be prepared from chemical vapor deposition and then C-template will be removed to form mesopores in SiO2 shell. This route breaks such catalysts traditionally prepared via wet-chemical route. For investgating its growth mechanism, the synthetic conditions, such as resources concentrations, composite and reactive tempature, will be modified and their morphologic changes will be characterized to find out mixture, heat transportion and nucleation mechanism in order to modify the morphology of the novel catalyst, such as thickness, mesopore volume and mesopore distribution of shells, and diameter and crystal type of cores. The composite of the synthesis gas touching the core will be modified and dispersivity of catalysts will be improved to avoid their sintering. Thus, the catalyst with high catalysis and stability will be obtained.alyzed to form lower olefins. Thus designation and fabrication of novel catalysts with high selectivity, transformation ratio and stability, can enhance the efficiency of the reaction. In this project, we propose to develop a novel kind of catalyst and investgate its growth mechanism. This nano-composite catalysts has a ferrous core encapsulated with a mesoporous SiO2 shell. For preparing nano-composite catalyst, ferrous core encapsulated with Si/C shell will be prepared from chemical vapor deposition and then C-template will be removed to form mesopores in SiO2 shell. The prepared silica shell can modify composition of synthesis gas impacting ferrous cores and isolated ferrous cores from other ones to avoid sintering, which ensure both transformation efficiency and stability of catalysts. To approach this purpose, the thickness, mesopore volume and distribution of silica shell should be modified. Hence, the growth mechanism of cores and shells, and their interact should be investigated to approach designaion and morphological modificaion of novel catalysts, leading to enhancement of their catalysis.

由煤基合成气生产低碳烯烃的关键技术是催化剂的设计与制备。本申请拟开展新型铁基核壳催化剂（Fe@SiO2）合成及其催化合成气生产低碳烯烃应用的研究。提出了碳模板法制备该纳米复合催化剂的新路径：首先化学气相沉积法合成核壳结构颗粒，外壳为碳和氧化硅的复合结构，内核为铁基纳米颗粒；再将碳除去使氧化硅外壳产生介孔，形成介孔氧化硅外壳包裹铁基纳米颗粒的复合催化剂。本路径打破了该类催化剂传统制备依赖液相合成路径的局限。为明确催化剂生长机理，拟调节原料浓度、成分和反应温度等合成条件，表征其形貌变化，揭示原料的混合、热质传递和形核长大等问题，从而实现对新型催化剂形貌调控，如外壳的厚度、介孔孔容和孔径分布，内核粒径和晶型。达到利用介孔氧化硅外壳调控与内核接触的合成气成分，并分隔铁纳米颗粒防止严重烧结，保证了催化剂的转化率和稳定性。

本项目将从微观组装的角度出发，研究碳硅外壳包裹铁基颗粒形成纳米核壳结构的生长机制。通过化学气相沉积合成核壳结构颗粒，外壳为碳和氧化硅混合结构，内核为铁基纳米颗粒；再除去模板使外壳产生介孔，形成介孔外壳包裹铁基纳米颗粒的复合催化剂结构。.通过温度及原料配比，实现了化学气相沉积调控合成铁基核壳颗粒:碳硅外壳包裹铁基颗粒、含氮掺杂结构碳外壳包裹铁基内核的纳米颗粒：其渗碳体内核粒径在10-80nm范围内，平均石墨外壳厚度在1.2-5nm范围内，可以有效控制以及含硫掺杂结构碳外壳包裹硫化亚铁内核的纳米颗粒：其硫化亚铁内核粒径在30-80nm范围内，平均石墨外壳厚度在3-8nm范围内，可以有效控制。.将含掺杂结构碳外壳包裹铁基内核的纳米颗粒中掺杂结构部分移出形成碳基介孔外壳包裹铁纳米颗粒，碳基介孔外壳包裹铁纳米颗粒中外壳形成介孔结构较容易，不需额外工序在催化合成气时就能完成外壳开孔；碳硅外壳包裹铁基颗粒中除碳需要额外空气氧化，对铁基内核破坏较大；在高压 (2MPa)反应中，本项目所制使碳基介孔外壳包裹铁纳米催化剂转化率达到34.68%（除去二氧化碳转化率的数据），C2-C4 烯烃的选择性达到49.73%。.通过调控生长铁基核壳颗粒可衍生出其它纳米材料，除去内核铁基颗粒获得平均石墨外壳厚度在1.2nm超薄壁氮掺杂石墨纳米笼。超薄壁石墨结构可有达到优化了锂电嵌锂/脱锂通道的目的，其中氮掺杂薄壁石墨纳米笼作为锂电负极材料表现出了良好的电化学性能：在0.5 A/g下充放电比容量达到760 mA h/g；10 A/g下比容量达到250 mA h/g。上述超薄壁氮掺杂石墨纳米笼，其氮掺杂石墨纳米笼经过真空热处理开孔后，石墨纳米笼的比表面积均有显著提高，由于多孔壁石墨结构可有效提高电解液中离子的扩散能力，使得电容性能有了大幅提高，当电流密度为0.1 A g-1时，多孔壁石墨纳米笼的比电容高达370 F g-1，未开孔氮掺杂石墨纳米笼的比电容仅为297 F g-1。当电流密度提高到1.0 A g-1，多孔壁石墨纳米笼比电容仍高达230 F g-1。这些新型碳纳米材料还可以作为直接甲醇燃料电池电催化剂载体使用，催化效能比商业催化剂提高约1.5倍。