基于纳微三重核-壳结构催化材料的氢溢流和加氢脱硫机理研究

To reduce the sulfur level in diesel fuel to 10 ppm and lower, even highly refractory sulfur compounds, such as 4,6-dimethyldibenzothiophene, must be almost completely removed from the fuel. This project proposes to design a new triple core-shell Pt-zeolite-CoMo microstructured catalytic material for the hydrodesulfurization of diesel fuel. The innovation of this project is that active hydrogen is generated by highly active Pt nanoparticles and that the hydrogen flows to CoMo sulfide nanoparticles through a molecular sieve membrane and there promotes the generation of active hydrodesulfurization sites. In this way, a low-temperature, high-activity new hydrodesulfurization catalyst is constructed. The triple core-shell structure comprises a core layer consisting of a noble metal catalyst (that activates hydrogen), an intermediate molecular sieve layer, which acts as a protective layer (with a pore size less than 0.36 nm, it allows only hydrogen to pass), and a shell layer of a Co-Mo catalyst that provides hydrodesulfurization reaction sites. The intermediate zeolite layer ensures the continuous release of active hydrogen and avoids the poisoning of the precious metal. Multi-level "hydrogen spillover" (from precious metal to zeolite membrane to Co-Mo) and double catalyst synergy (precious metal and Co-Mo) will give a higher activity and longer life than of the traditional hydrodesulfurization catalyst. The new design of a hydrodesulfurization catalyst will allow studying the essence of “hydrogen spillover”, describing its delivery mechanisms and understanding the synergy between the catalysts

为实现柴油的超深度加氢脱硫，须对柴油馏分中最难脱除的、具有空间位阻效应的4,6-二甲基二苯并噻吩（4,6-DMDBT）等含硫化合物有效的脱除。本项目提出新型的Pt-分子筛-CoMo三重纳微核-壳结构催化剂用于柴油的加氢脱硫反应。创新思路在于利用贵金属Pt纳米粒子低温、高活化氢的特性产生活性氢，并通过分子筛膜溢流到CoMo硫化物纳米粒子上，促进加氢脱硫活性位的生成，从而构筑低温、高活性加氢脱硫新型催化剂。所谓三重核壳结构催化剂包括核层部分贵金属（活性氢的产生区）、中间层分子筛保护膜和活性氢传递介质以及壳层部分Mo（Co-Mo）（加氢脱硫反应区），利用多级“氢溢流”(贵金属-分子筛膜-Co/Mo)的传递和双催化剂（贵金属和Co-Mo）的协同耦合作用，显著提高传统加氢脱硫催化剂的活性和选择性。该项目为研究“氢溢流”本质、阐述其传递机制以及理解催化剂间的协同作用等方面提供了研究模型。

为实现柴油的超深度加氢脱硫，本课题开发了一种新的核-壳结构催化材料的构筑方法---凝胶覆盖法并将该方法普及化；随后，制备了新型的Pt-分子筛-CoMo三重纳微核-壳结构催化剂，用环己烯的加氢反应作为反应模型，揭示了 “氢溢流”本质、阐述其传递机理和作用机制。按照研究计划进行了模型含硫化合物在膜限域的纳微核-壳结构催化材料上的加氢脱硫反应并探讨了加氢脱硫反应机理---利用多级“氢溢流”(贵金属-分子筛膜-Co/Mo)的传递和双催化剂（贵金属和Co-Mo）的协同耦合作用，显著提高传统加氢脱硫催化剂的活性和选择性。.具体包括如下四个方面：.第一、建立和发展一种绿色的合成法制备纳米聚集态分子筛材料并揭示了分子筛成核和晶化单独进行的生长机制；第二、在纳米晶的合成基础上，研发了四种单层膜和复合膜限域的纳微核-壳结构催化材料的构筑方法、形成机理与调变规律；第三、研究了ZIF-67@Pt/Al2O3催化剂对烯烃加氢的反应活性和选择性的影响；第四、制备出一种高效耦合型加氢脱硫催化剂，研究了氢溢流对传统催化剂CoMoS的影响以及氢溢流的传递过程和机制。