合成气一步转化制柴油馏分的高选择性催化剂的研究

Fischer-Tropsch (FT) synthesis is a key step for the indirect transformation of coal, natural gas, into hydrocarbon fuels and chemicals, by syngas (CO/H2). However, some challenges still remain in catalysis for FT synthesis. The control of product selectivity is one of the biggest challenges. Recently, we have carried out systematic studies on bifunctional catalyst which consisted of novelly acid support and Ru nano-particles with the aim to improve the product selectivity on the FT synthesis. And the selectivities to diesel fuels or gasolines were very high on the bifunctional catalysts. However, the effects of the bifunctional catalyst on product selectivity were unclear. And so far, there were little studies related to one-step synthesis of diesel fuels from syngas under the bifunctional catalyst. On this basis, we will develop a novel catalyst based on hierarchical zeolite which can tune the abilities of CO hydrogenation and secondary-cracking reaction in FT synthesis. We expect an excellent result on high selectivity to diesel fuels. As for catalyst preparation, the first key process is how to prepare the hierarchical zeolite with uniform mesopore and tunable acidity. And many different methods will be investigated. The secondary key process is how to well confine the active Co nano-particles in the mesopore of support through different methods. Through the above processes, the optimized preparation method which can tune the properties of catalyst will be confirmed. And we will explore the effects of kind of zeolites, acidity, mesopore structure, location of active metal on the catalytic performance. Further, the modification of catalyst will be studied based on the above relationship.

费托合成是煤/气经合成气间接转化制燃料及化学品的关键过程。目前针对费托合成的基础研究仍存在一定挑战，其中关键的科学问题之一是产物选择性的调控。据申请人最近研究发现，在以新型酸性材料为载体负载Ru构建的双功能催化剂上，可以获得很高的汽油或柴油馏分选择性。然而双功能催化剂的作用本质尚不清晰，此外涉及合成气一步制备柴油馏分的研究工作极少。本项目将在前期研究的基础上，进一步构建具有CO加氢和二次裂解功能的多级孔分子筛限域的新型催化材料，以此催化合成气一步转化获得高选择性的柴油馏分。具体将重点研制具有规整介孔且酸性可调的多级孔分子筛，研究其制备方法和调变其性质的方法；并以具有应用前景的Co替代Ru，通过考察不同的制备方法将Co纳米粒子限域于介孔孔道内；最终确定可控的催化剂制备路线。研究多级孔分子筛的种类、酸性质、介孔结构以及活性相的落位与其催化转化合成气制柴油馏分性能的关联，以此为基础改进催化剂。

经合成气(H2 + CO)催化转化制备液体燃料和化学品是煤、煤层气、页岩气和生物质等非石油碳资源转化利用的最可行的途径之一。对于合成气制碳氢化合物的费托合成反应，产物选择性的调控被公认为极具挑战性的科学难题。.本项目针对合成气直接转化制柴油馏分液体燃料，提出金属活性位上发生的氢解反应在合成气转化反应中的新认识，并利用氢解反应设计合成气高选择性转化制柴油馏分双功能钴催化剂。研制出Co/Na-meso-Y催化剂，合成气转化制C10-C20柴油馏分烃选择性达到60%；经Mn助剂修饰后选择性达到65%，且经1000 h评价催化性能保持稳定。对于合成气转化Co、Ru催化剂上存在的产物选择性差异，研究发现Co和Ru催化剂上氢解反应强弱是影响催化性能的关键。Co催化剂上氢解能力强，易产生甲烷；而Ru催化剂因CO强吸附导致氢解能力弱，显示出低甲烷选择性。Ru催化剂经Ir修饰后可促进氢解反应，C10-C20选择性接近75%。.项目进一步发展反应耦合策略，构建合成气经甲醇中间体直接转化制低碳烯烃、芳烃等碳氢化合物的新型双功能催化剂体系。研制了Zn-ZrO2/SAPO-34双功能催化剂，合成气一步转化制低碳烯烃的选择性达到70%以上。研制了Zn-ZrO2/H-ZSM-5双功能催化剂，合成气直接转化制芳烃的选择性达到80%，且芳烃选择性可调，轻质芳烃BTX选择性接近50%。Zn-ZrO2/H-ZSM-5催化剂性能稳定，1000 h寿命评价无显著变化。.项目通过系统的基础研究，深化了对合成气转化制碳氢化合物过程的认识，特别是各功能活性位作用及匹配规律方面取得了较好的进展，为进一步设计和制备具有高选择性的催化剂体系提供一定的科学基础。