新型富缺陷空间伸展Co-Mo-S活性组分的结构设计、可控制备及柴油深度加氢脱硫研究

Refineries are facing the challenge of production of clean fuel along with the increasingly stringent environmental regulations. However, the conventional catalysts for hydrodesulfurization are unable to remove the high molecular weight sulfides such as 4,6-dimethyldibenzothiophene because of the stereo-hindrance effect of substituents attached to aromatic rings. In the present project, some defect-rich specific morphologies Co-Mo-S active components with stretch and distortion in space are designed, instead of the conventional lamellar structure Co-Mo-S. A novel controlled-preparation technology, the combination of sing-source molecular precursor and hydrothermal/solvothermal synthesis, is developed to make the mutil-level control of 3D morphology, structure, and size of Co-Mo-S active component and the targeted-preparation of highly efficient active structure for hydrodesulfurization of 4,6-DMDBT. The combination of stoichiometric calculation and deep hydrodesulfurization of diesel oil, is applied to reveal the effects of morphology, structure, and preparing process of the Co-Mo-S components on their catalytic performance. The effect mechanism of the structure and electrical characteristic of Co-Mo-S component on the activity and selectivity of hydrodesulfurization for large molecules contained sulfur will be investigated. The structure-activity relationship of Co-Mo-S component will be also established. It is possible to bring an innovation of the design of catalyst structure to a certain degree. The aim of this project is to establish the theoretical and technological foundations of the efficient hydrodesulfurization for stereo-hindrance sulfides and the controllable preparation of morphology and structure of Co-Mo-S active components.

环保法规日益严格，燃油清洁化生产已成为炼厂的严峻挑战，传统加氢脱硫催化剂难以脱除柴油中具有空间位阻效应的4,6-DMDBT类含硫化合物。本项目针对传统Co-Mo-S活性组分调控迂于片层结构的局限，设计具有一定扭(弯)曲程度、空间伸展而富缺陷的Co-Mo-S特定形貌结构。采用单源分子前驱体法和水热/溶剂热法相结合的控制制备技术，对Co-Mo-S活性组分的三维形貌、结构、尺寸等进行多层次调控，以实现对4,6-DMDBT类含硫化合物加氢脱硫所需高效活性结构的定向制备。结合化学计算方法及柴油脱硫反应，揭示Co-Mo-S的空间形貌结构、电子性质等对位阻含硫化合物脱硫活性和路径选择性的影响机制，构建Co-Mo-S活性组分结构与催化性能的构效关系。本项目的实施有望形成一种Co-Mo-S活性组分的分子结构设计新思路，为位阻类含硫化合物的高效脱除和Co-Mo-S活性组分的形貌结构可控制备奠定理论和技术基础。

首先，采用单元分子前驱体法结合水热法制备了形貌可控的MoS2，考察了不同反应时间、溶剂种类、表面活性剂种类、pH对MoS2晶型和形貌的影响；探究了典型代表MoS2-SDBS、MoS2-CTAB、MoS2-SDS的加氢脱硫活性和其微观结构的关系，结果表明，MoS2的加氢脱硫活性和其平均晶纹长度、分散度、边角活性位点比值呈正相关，与平均层数呈负相关，具有更短的晶纹、更高的堆积程度和更大分散度的MoS2-SDBS具有更优异的加氢脱硫活性。在此基础上，通过共沉淀法成功合成了单源分子前驱体(MoO2)0.7Co0.3(DDTC)2和超薄纳米片自组装的花状CoMoS催化剂。发现通过一步法引入Co时，Co元素会与MoS2活性组分接触，生成CoMoS活性相，显著提高了CoMoS催化剂的HDS活性。随着水热时间、温度的增加，促进了催化剂中MoS2活性组分和CoMoS活性相的形成。在水热时间、温度分别为24 h，220℃，所得CoMoS催化剂具有规整的纳米花状结构，产物表面超薄纳米片提供了大量的HDS活性位点，其4,6-DMDBT转化率高达99%。. 研究发现，通过添加不同的表面活性剂、改变溶剂PH值等，可以改变催化剂中MoS2活性组分的微观结构，进而改变MoS2晶格条纹长度和edge活性位的数量。将不同形貌的CoMoS产物用作HDS反应催化剂，实验和理论计算结果表明，CoMoS催化剂的HDS活性与MoS2活性组分的平均堆垛层数成负相关，具有更少的堆垛层数的CoMoS-4催化剂，表现出更优异的HDS活性，而CoMoS催化剂的DDS路径选择性与MoS2晶格条纹长度成正相关，长的MoS2晶格条纹意味着更高的edge活性位数量，具有较长的晶格条纹长度的CoMoS-PEG-CTAB和CoMoS-CTAB催化剂，表现出显著提高的DDS路径选择性。