新型核-腔-壳Co/SiO2@void@ZSM-5纳米反应器构建及其协同催化合成气一步高选择性合成汽油

合成气一步高选择性合成汽油是制约间接法煤制油工艺发展的关键技术瓶颈。费-托合成活性相与ZSM-5分子筛相耦合的核壳型催化剂，虽然能提高汽油段产物选择性，但存在反应相关分子在核外表面和壳层内部扩散受限制、Co与ZSM-5生成难还原物种导致活性下降等问题。本项目使用具有MOF结构的ZIF-67衍生制备ZIF-67/SiO2作为核的前驱体并在其外包覆SiO2层，高温碳化后再水热晶化形成ZSM-5壳层，通过碱刻蚀去除SiO2层在核与壳间形成空腔，构建新型核-腔-壳Co/SiO2@void@ZSM-5纳米反应器。基于介孔SiO2限域的丰富Co活性位、利于扩散的空腔和性能可调的ZSM-5壳层，能大大提升反应活性和汽油选择性。将探讨核、腔、壳功能区的作用机制及影响催化性能的关键结构因素，明确其对活性和汽油选择性的影响机制及Co活性位与ZSM-5酸性位的协同作用机制，为合成气一步高选择性合成汽油提供基础。

Highly selective catalytic one-step synthesis of gasoline from syngas is a key technical bottleneck for restricting the development of indirect coal-to-liquids process. Although the core-shell structure bifunctional catalyst combining the active phase for Fischer-Tropsch synthesis with ZSM-5 zeolite can improve the selectivity of gasoline products, there are some problems such as the diffusion of reaction related molecules on the outer surface of the core and inside the shell is restricted, the formation of hardly reducing species from Co and ZSM-5 interaction leads to the decrease of activity. In this project, ZIF-67/SiO2 derived from ZIF-67 with MOF structure was used as the precursor of the core Co/SiO2, which was covered with SiO2 layers. After high temperature carbonization, a ZSM-5 shell encircled ZIF-67/SiO2 was formed using hydrothermal crystallization method. A void space between the core and shell was formed by alkali etching the SiO2 layer between core and shell to construct a new type core-void-shell Co/SiO2@void@ZSM-5 nanoreactor. The abundant active Co sites confined by mesoporous silicon dioxide was used as the core, the void space favorable for diffusion and the ZSM-5 shell with adjustable performance could greatly improve the reaction activity and gasoline selectivity. The functional mechanism of core, void space and shell as well as the key structural factors affecting the catalytic performance will be discussed. The mechanism of their influence on the activity and gasoline selectivity and the synergistic effect of Co active site and ZSM-5 acid site will be clarified. This will provide the basis for one-step highly selective synthesis of gasoline from syngas.