两相共生共存分子筛及结构效应在催化裂化反应中的作用

As we know, the multiple types of active sites in co-crystalline zeolite structure plays very important roles in catalytic reaction due to the synergic effect of active centers from different kind of zeolites. In this program, the novel co-crystalline structures have been designed and in situ synthesis strategy have been carried out to obtain the co-crystallined material by intergrowth of two different zeolites. The both zeolites in co-crystalline material display not only their individual microscopic structure features, but also give prominence to their microstructure complementarity, resulting in unique catalysis performance..Fluid catalytic cracking (FCC) is one of the most petroleum refining processes, development of the high effective catalyst and its catalyst additive is very desirable all the time. Based on the structure requirement of FCC catalyst additive for enhancement of propylene and gasoline octane number，the novel co-crystalline zeolite material (such as EUO/MRE, MFI/MRE co-crystalline structures) has been designed in this program. For example, EU-1 (EUO) zeolite displays 1-D channel system with 10-MR openings (4.1×5.4 ?) running along the direction connected to the side pocket by 12 MR in the (001) direction.The 12-MR side pockets are 6.8 ×5.8 ? wide and 8.1 ? deep. This intriguing topologic structure of EU-1, intermediate between 10-MR medium-pore zeolite and 12-MR large-pore zeolite, imparted it curious catalytic performance in acid-catalyzed reactions. ZSM-48 (MRE) has only 1-D 10-MR straight channels (5.3×5.6 ?), presenting disordered crystal structures. Their co-crystalline structure features as following advantages: Offering different kinds of active sites, feasible control of acid properties; creating micro-micro-mesoporous structure and increasing the accessibility of active sites, resulting in high propylene selectivity and optimized gasoline product distribution. In virtue of zeolite synthesis method in quasi-solid state system, and the synthesis chemistry of co-crystalline structure including precursor directing, template assembly, and process control and so on, developing a meso-macroscopical compositive technique. By using the advanced SAXS theoretical and experimental technique, developing the novel characterization method of the microstructure for the co-crystalline zeolite..The applicant believes that the new hierarchical composites will be created, and with this basis, the structure aberrance and active variation, arising from the co-crystalline formation will be investigated, and their catalytic cracking performance will be evaluted in detail. These studies will pave a way for enhancement of the FCC catalyst technique.

根据多活性中心协同作用在反应中的潜在优势，原位构筑两相共生共存分子筛，使两类分子筛发挥各自结构特点，而且进行微结构互补，互调，从而带来特殊的催化效果。本项目设计针对FCC催化剂助剂材料的两相共生共存分子筛体系，可提供多活性中心，易调控分子筛酸性质；营造微孔－微孔－介孔多级结构的反应场所，提高活性位的可接近性，提高分子筛择形能力和平衡二次裂化能力，从而发展共生共存分子筛晶体结构、活性位结构和晶粒大小、空间维度等微观-介观集成方法。借助于类固相晶化方法制备分子筛技术思想，包括前躯体导向、模板组装、过程控制等特征的分子筛制备化学内容，发展晶面择优取向、形貌结构调控的介观-宏观集成技术。利用先进的SAXS技术，丰富分子筛真实微观结构表征的内涵。笔者深信，项目实施将形成多维化、多尺度、高活性的分子筛新体系，在此基础上对其形成过程中结构畸变、活性位变化以及构效关系的研究，提高FCC催化剂的研究水平。

复合分子筛是指具有两种或两种以上分子筛相的复合晶体，主要包括共生分子筛（co-existence zeolite）和共晶分子筛（intergrowth zeolite）两类。复合分子筛不仅具有单一分子筛独特的孔道性质和酸性质，而且两种晶体在共晶或共生过程中产生微结构变化并具有一定的协同效应，在催化反应过程中体现出特殊的催化性能，因此在石油化工行业中具有潜在的应用前景。然而，微孔-微孔复合分子筛的合成仍存在一些难点，如何筛选不同晶相复合、如何实现不同晶相稳定的共生/共晶过程，如何对产品微结构性质的调控等关键科学问题。.本项目基于择形分子筛（ZSM-5、EU-1、ZSM-48），研究构建共生共存分子筛晶体结构，包括活性位结构和晶粒形貌、空间维度等微观-介观集成方法。.设计特定晶种法合成了EU-1&ZSM-48共生分子筛。所得共生分子筛具有不同晶相比例和较长的晶化稳定期。揭示了EU-1&ZSM-48共生分子筛可控合成及存在较长晶化稳定期的原因。共生过程使得共生分子筛中介孔含量明显增加，介/微孔比例得到有效调变，同时表现出更多的酸量和更高的酸强度。正己烷转化率96.5 wt%，分别比EU-1、ZSM-48以及机械混合样品高。在石脑油裂解反应中，共生分子筛石脑油转化率分别比纯相EU-1和机械混合样品高出4.0和8.7个百分点，更高乙烯、丙烯收率以及丙烯/乙烯比；采用双模板法合成了ZSM-5/ZSM-48共晶分子筛。该共晶分子筛具有纳米薄层状ZSM-5晶体与纤维状ZSM-48晶体垂直穿插、相互交错生长的共晶特征。得到了具有不同硅铝比和不同晶相比例的ZSM-5/ZSM-48共晶分子筛。在正己烷裂解反应中，共晶分子筛与商业ZSM-5和纳米薄层ZSM-5表现出几乎相同的双烯收率和稳定性，且均明显高于机械混合和ZSM-48样品。石脑油催化裂解表明，共晶分子筛具有与纳米薄层ZSM-5相近的双烯收率和稳定性，二者初始双烯收率约为57 wt%，反应12 h之后，二者双烯收率仍在50 wt%左右。在整个反应过程中前者丙烯/乙烯比明显高于后者；通过研究分子筛晶化动力学，筛选EU-1活化能相近的ZSM-5分子筛模板剂，实现了ZSM-5/EU-1共生共存分子筛的合成和晶相比例的有效调变。己烷裂解反应中该共生分子筛表现出比参比样品更高的活性稳定性和低碳烯烃选择性。