胺热共模板策略合成SAPO分子筛及其MTO催化性能研究

Molecular sieves are an important class of crystalline porous materials and play a significant role as catalytic material. The innovation of their synthesis methodologies will provide new opportunities for the development of novel structures as well as for the improvement of physicochemical properties of known molecular sieves. In this project, based on the aminothermal methodology initiated by our laboratory, we further innovatively combine the aminothermal synthesis with the co-templating strategy. This innovation will not only open up more extensive space for the aminothermal system, but also will for the first time help establish the theoretical foundation for the study of dual-template synthesis. The project is proposed to study the different matching characteristics of a variety of amine combinations under aminothermal environments. Combined with a research into the crystallization process, we attempt to reveal the crystallization mechanism and inherent law of the cooperative/competitive effect between different amine molecules for the structure-directing synthesis of molecular sieves, which could further offer us the theoretical basis and guidance for the controlled synthesis of known molecular sieves and innovative synthesis of novel molecular sieves. The proposed project will also combine the development of novel synthesis methodologies with the discipline of catalysis. More specifically, SAPO-34, the catalyst for the methanol-to-olefins industrial process, is selected as the research object. Via the establishment of the relationship model of aminothermal conditions-physicochemical properties-catalytic properties, we aim to realize the precise tuning and controlling of the physicochemical and catalytic properties of the synthesized products, and in turn obtain molecular sieve catalysts with improved performances. The research work will develop new synthetic method, and bring new ideas for the optimization of MTO catalyst. It has great scientific significance and practical value.

分子筛作为一类重要的无机催化材料，其合成方法的创新将为分子筛新材料的开发和已知分子筛的物性优化提供新的机遇。本项目基于我们首创的胺热合成法，创新性地将共模板策略与胺热合成相结合，不仅为胺热合成体系开辟更广阔的空间，同时也将为双模板体系磷酸硅铝分子筛（SAPO）的合成研究构建知识基础。本项目拟系统研究不同性质的有机胺在胺热环境下的匹配特点，并结合晶化过程研究，揭示有机胺相互协同/竞争导向生成分子筛的晶化机制和内在规律性，为分子筛的控制合成和新型分子筛材料的创制提供理论指导。另一方面，新的合成方法将与催化学科紧密结合，即以甲醇制烯烃(MTO)过程的分子筛催化剂SAPO-34为研究对象，以两种模板剂的组合作为主要调变手段，通过建立“合成—产品物性—催化”三者间的理性联系，实现对晶化产品催化性能的有效调控。本项目的研究将开拓分子筛合成新方法，并为新一代MTO催化剂的开发带来研究新思路。

分子筛新材料和新合成方法的开发一直是分子筛领域的重要研究方向。本项目将共模板策略与胺热合成方法相结合，不仅为胺热合成体系开辟更广阔的空间，同时也为双模板体系磷酸硅铝分子筛（SAPO）的合成研究构建相关知识基础。通过本项目的开展，对胺热共模板体系合成SAPO分子筛获得的认识总结如下：1）不同的模板剂组合通过调变，在较宽的范围内均可以得到SAPO-34。具有较高电荷密度的小分子有机胺具有更强的进入分子筛晶体的能力；随着有机胺组合中小分子有机胺用量的增加，产品中的硅含量上升，收率下降；以醇胺为溶剂的合成体系，产品的硅含量要高于烷基胺合成体系；醇胺比烷基胺具有更高的进入分子筛晶体的能力，这可能与醇胺分子自身具有较强的极性有关。2）在以三乙胺为溶剂和模板剂的合成体系中，添加哌嗪类有机胺作为共模板剂，在少量晶种的辅助下可成功合成纳米SAPO-34。产品具有纯正的CHA晶相和以Si(4Al)为主体的硅环境，在MTO反应中显示了明显延长的催化寿命以及良好的低碳烯烃选择性。3）通过采用结构精修的方法确定分子筛中模板剂的构象，并依据获得的主客体信息来推测合成所需的模板剂结构特点，实现了分子筛合成有机胺模板剂的理性挖掘。4）以有机醇胺为模板剂和主体溶剂，合成获得了多种SAPO分子筛新材料，包括具有CHA/GME共晶结构的DNL-8分子筛、SAPO-17/SAPO-35共晶分子筛、SAPO-17/SAPO-56共晶分子筛、超大孔SAPO-DNL-1等。这些结果说明有机醇胺易与其它有机胺产生协同作用，且由于两者组合调变的空间大，非常有利于分子筛新材料的发现。此外，具有较高电荷密度的有机胺或季铵盐/碱作为共模板剂也更易和醇胺产生协同作用。这些关于胺热共模板合成研究的认识，不仅有助于分子筛合成方法的创新和获得分子筛新材料，还为 MTO 催化剂的性能提升和升级换代提供了研究新思路。