基于过渡金属硫化物活性相精确构建和识别的柴油深度加氢脱硫反应机理研究与催化剂设计基础

The supported catalyst of transition metal sulfides(TMS) is an important type of hydrogenation catalyst to produce of ultur low sulfur clean diesel. The conventional processe for the fabrication of TMS active phases often adopt oxysalts as precusor. That would result in multi-types of metal sulfides in the active phase. And the regulation of the micro-components of active phase is very difficult. Moreover, the supports often adopt the non-ordered pore oxides, that leads to the low contrast of HRTEM images. Therefore, the microstructure of active phase and smaller active species could not be detected exactly. In the present proposal, the TMS active phases would be fabricated confinedly in meso-porous metarials with one dimensional channels, and adopted transition metal thiosalt as precusor. There are two advantages in this research, on the one hand the contrast of HRTEM images could be increased using ordered pore materals as matrix, and on the other hand the single component coud be obtained conveniently in preparation of catalyst through thiosalt as procusor. These two advantages could be benefit to carry out more in-depth study. The research results have a theoretical significance in revealing the nature of TMS active phase and the structure-activity relation between TMS active phase and catalytic hydrodesulfurizaion performance, and could also provide theoretical basis for the development of new TMS catalysts with higher actvity.

负载的过渡金属硫化物是用于生产超低硫清洁柴油的关键加氢催化剂。通常采用金属含氧盐为前驱物构建过渡金属硫化物活性相，活性相中金属硫化物种类较多，难以精确调控活性相微观组成；并且采用无规整孔道的氧化物为载体，在进行高分辨透射电镜分析时载体与活性物种之间衬度不明显，难以精确分辨较小的活性物种及其微观形貌，从而导致对活性相微观结构与其脱硫活性的构效关系认识难以深入。因此，本项目提出在具有规整孔道的介孔材料孔道内采用金属含硫盐限阈构建过渡金属硫化物活性相，规整孔道可以提高高分辨电镜分析时的衬度，采用含硫盐作为前驱物可控制构建组成较为确切的活性相，两个优势结合起来有利于更为深入、细致地研究过渡金属硫化物活性相微观精细结构和加氢脱硫反应机理及其构效关系。该项目的开展有助于揭示过渡金属硫化物活性相本质，深化对其微观结构与加氢脱硫反应性能构效关系的认识，并可为高性能柴油深度加氢脱硫催化剂设计提供理论基础。

过渡金属硫化物加氢催化剂是石油资源高效利用的重要催化剂。通过项目的研究主要取得如下成果：采用过渡金属含硫盐低温转化法成功构建了限域于SBA-15孔道内的MoS2晶簇堆积层数和晶片长度均一的活性相，SBA-15孔道内的MoS2晶簇的堆积层数集中为4-5层，而晶片长度集中为5nm左右。在DBT的加氢脱硫实验中，MoS2/SBA-15催化剂具有比MoS2/Al2O3催化剂更高的活性和选择性。浸渍顺序能够影响活性相的结构和尺寸，采用共浸渍法制备的硫化型CoMo催化剂表面活性相分散更均一，颗粒更小，具有最优的加氢脱硫活性和选择性。同时，证实催化剂表面CoMoS活性相的角位为加氢脱硫活性位，而边位为氢解脱硫活性位。CoMoS相的拐角位的硫非常容易脱除从而形成多配位不饱和的硫空穴，更利于氢气的吸附解离，从而归属为加氢活性中心；而棱边位（Edge）上的CoMo协同作用，促进了-SH基的产生，极大地促进了加氢脱硫反应而对烯烃加氢反应影响较小，从而归属为氢解活性中心。距离小于等于微米时，氢溢流效应的增强有利于加氢脱硫沿DDS路径反应。随着两种硫化物之间的距离减小，催化剂活性增大且DDS路径选择性增加，双金属催化剂在加氢脱硫过程中体现的协同作用可以采用氢溢流模型的理论解释：Co9S8为供体，活化氢气后生成Hso“溢流”至MoS2，MoS2被还原之后产生活性位。随着Co、Mo两种硫化物之间的距离减小，其协同作用随之增强，即氢溢流效应增强，导致催化剂活性增加，反应逐渐趋向于DDS路径进行。这些研究结果有助于揭示过渡金属硫化物活性相本质，深化对其微观结构与加氢脱硫反应性能构效关系的认识，可为高性能柴油深度加氢脱硫催化剂的设计提供理论基础。