沸石笼中金属簇的氢溢流和多级孔沸石表面酸性的协同效应

Selective ring-opening of ployaromatic hydrocarbons to reduce the aromatic content and increase the desiel cetane index is the important process for diesel improvement. But in this catalytic process, the used noble catalysts are easily poisoned by sulfur even at a trace level. Therefore, how to increase the sulfur-tolerance of the noble catalysts in this catalytic process is a challenge. In the proposed project, a novel strategy, involving encapsulation of noble metal clusters within sodalite crystal and decorated zeolites, then overgrowth of a hierachical zeolite shell with tunable pore structure and acidity, is suggested for the preparation of high sulfur-tolerance catalysts in selective ring-opening of ployaromatic hydrocarbons. According to the proposed strategy, organosulfur compounds even H2S molecules are selectively excluded from the small pores. Thus, encapsulation within zeolite protects clusters from contact organosulfur and H2S and increase the sulfur-tolerance ability of the prepared catalysts. While H2 molecules can enter into sodatite or the decorated zeolites, be dissociated on metal sites, and be transported between the core and the formed shell by hydrogen spillover. Hence, the selective ring opening of ployaromatic hydrocarbons on the prepared hybrid catalysts can be realizes via the synergistic effects of hydrogen spillover and the acidic sites from the overgrown zeolite shell. It is expected that the the project can provide a new route for the preparation, development and industrial application of novel catalysts with high sulfur tolerance, activity and selectivity in selective ring opening of polyaromatic hydrocarbons.

本项目针对稠环芳烃加氢反应中的选择性开环和抗硫性等关键问题，在设计负载贵金属双功能催化剂的过程中，提出了将贵金属纳米簇封装于小孔方钠石或经孔口修饰的沸石笼中，并以此为核在其表面生长具有酸性能可调的多级孔沸石薄膜壳层，制备具有以抗硫氢解离催化剂为核和择形酸催化剂为壳新型复合结构的选择开环催化剂。该思路利用SOD和经修饰后沸石较小孔口对H2S分子（包括有机硫）进入其孔道所具有的限制作用，来阻止封装于沸石笼中的金属簇与硫化物相接触，提高催化剂的抗硫性能，同时利用所筑沸石壳层的酸性中心可为活性氢的迁移提供路径有利于氢溢流进行的这一特点，将沸石笼中金属簇的氢溢流和沸石壳层酸性功能有机地结合起来，通过二者的协同作用来实现对稠环芳烃的选择开环。该项目的实施可为高抗硫性能、高催化活性和选择性的新型稠环芳烃选择开环催化剂的研制、开发和工业应用提供新的路径。

本项目立足于沸石笼中金属簇的氢溢流和沸石酸性功能之间的协同效应，通过对金属簇在沸石笼中的封装、封装金属簇沸石与酸性沸石载体的耦合、在封装金属簇沸石外壳层构筑和所制催化剂催化性能等几方面的研究，得到以下主要研究结果：1) 通过Pt@SOD与ZSM-5耦合制备出具有高抗硫性及选择性的环烷烃加氢转化催化剂，提出了涉及氢溢流效应的非传统环烷烃加氢转化机制；2）通过对Pt@NaA进行离子交换和耦合ZSM-5酸性载体，不仅制备出具有良好抗硫能力的萘加氢催化剂还可通过改变耦合方式对萘加氢裂化产物进行调控；3）采用外延生长法构筑了以负载Pd NPs的Silicalite-1沸石为核和ZSM-5为壳的核壳型催化剂和以在无二次模板剂的条件下合成的具有不同硅铝比的介孔ZSM-5为载体，制备了Pt/HZSM-5双功能催化剂，通过对这两类催化剂的结构和催化性能的研究，揭示了氢溢流效应与酸中心密度及酸位和金属组分邻近性的关系；4）揭示了SSZ-13的酸特性、孔结构及金属簇在SSZ-13中的定向落位等因素对所制催化剂催化性能的影响，并采用转晶晶化法合成出具有高外比表面多级孔纳米SSZ-13，拓展了催化剂性能的调控空间。上述研究结果可为高抗硫性能、高催化活性和选择性的催化剂的研制、开发和工业应用提供新的路径。

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