基于氢溢流机理的双金属耐硫型烷烃异构化催化剂的设计和可控制备

The development of alkane isomerization catalysts and processes has become important for the production of clean gasoline in China. As the most promising catalysts for the isomerization of light alkane, the traditional noble metal-promoted acid support catalyst suffers from the poor sulfur resistance and high cost, which will be resolved based on the hydrogen spillover mechanism in this project. Firstly, the Pt/α-Al2O3@Sodalite with core-shell structure will be designed and controllable synthesized. The cages of the nanosized sodalite shell are sufficiently small (0.3 nm) to exclude the smallest sulfur-containing molecules (hydrogen sulfide, 0.36 nm), while allowing hydrogen molecules (0.289 nm) and atomic hydrogen to diffuse in and out of the cages to allow hydrogen spillover. The Pt/Al2O3@sodalite core-shell material combined with traditional acid support will show high activity, stability, and high sulfur resistance in the isomerization of alkane. Secondly, taking into account the high activity of Pt sites in H2 adsorption dissociation, the second non-noble metal with high sulfur resistance will be introduced to the surface of acid support, acting as the adsorption sites for the dissociated H species. In this way, Pt/Al2O3@sodalite core–shell material (where hydrogen spillover starts) is used as active hydrogen emission sources, producing active hydrogen and transporting it to the non-noble metal-promoted acid support (where the spilled over hydrogen is used and the alkane isomerization occurs). The synergy between metal centers and acidic centers will be revealed to shed light on the structure-activity relationship of Pt/α-Al2O3@Sodalite+Me/acidic support catalyst in the alkane isomerization, which would facilitate the development of sulfur-resistant alkane isomerization catalysts.

烷烃异构化催化剂和工艺的开发已成为我国车用汽油清洁化的重要技术途径，金属-酸双功能催化剂是当前烷烃异构化催化剂研究开发的焦点。为了突破传统直接负载型金属-酸双功能催化剂耐硫性能差和贵金属含量高的瓶颈，本项目将基于氢溢流机理，设计合成具有核壳结构的Pt/α-Al2O3@Sodalite，利用壳层方钠石(Sodalite)的孔道限域作用，在允许H2通过壳层在Pt中心上解离吸附的同时，有效阻碍H2S与Pt接触。将Pt/α-Al2O3@Sodalite与酸性载体机械混合用于烷烃异构化反应，以期达到耐硫的目的。本项目还将充分利用Pt活性中心解离吸附氢气速率快的优势，降低催化剂表面Pt负载量的同时，向酸性载体表面引入耐硫的第二种非贵金属活性组分作为解离态氢物种的吸附场所，提高催化剂表面解离态氢物种的浓度，从而得到高活性的Pt/α-Al2O3@Sodalite + Me/酸性载体烷烃异构化催化剂。

烷烃异构化催化剂和工艺的开发已成为我国车用汽油清洁化的重要技术途径，金属-酸双功能催化剂是当前烷烃异构化催化剂研究开发的热点。以具有优异的热稳定性、大比表面积和择型催化功能的酸性分子筛为载体，在其表面负载贵金属活性组分制备得到的“金属-酸”双功能催化剂被认为是最具工业应用前景的异构化催化剂。其中，Beta分子筛的三维十二元环孔道结构和适宜酸性使其成为理想的烷烃异构化酸性载体。然而，常规Beta分子筛对高辛烷值双支链异构体的选择性仍不能满足工业需求。这主要是因为其狭长的微孔孔道限制了动力学直径较大的双支链异构体的晶内扩散，同时纳米晶堆积形成的晶间介孔使得双支链异构体在晶体内的停留时间过长，导致裂化副反应加剧。针对此问题，本项目采用碱处理法制备了梯级孔Beta分子筛，有效改善了载体孔道结构、减小晶粒团聚程度，降低了催化剂在正己烷异构化反应中的传质阻力，提高双支链异构体的选择性。项目执行期内在国际知名期刊上发表学术论文6篇，其中SCI收录6篇；授权发明专利3件，均超过项目申请时的预期成果数。本研究结果为改善微孔分子筛的传质性能，开发高双支链异构烷烃选择性催化剂提供理论基础。