天然黏土矿物原位可控合成低维纳米沸石及其催化性能研究

Low-dimensional nano-sized zeolites (nanosheets or nanofibers) exhibit extra high catalytic performance because of their shorter intracrystal pores and more accessible acid sites, compared to the conventional zeolites. Up to now, these low-dimensional nano-sized zeolites were commonly synthesized using specific and expensive organic templates, where the synthetic procedure for templates is always very complicated. Therefore, in this project we present a novel synthetic method for low-dimensional nano-sized zeolites from clay, based on our previous study about the successful transformation of ZSM-5 zeolites from clay. Lamellas of layered clay can be successfully converted to zeolite nanosheets after intercalating modification with polymers between lamellas. In addition, inert materials, such as carbon and polymer, can also be used to wrap clay nanomaterials obtained by the delaminating or disaggregation of clay for the in-situ transformation from clay to low-dimensional nano-sized zeolites. Due to the coating and padding of inert materials, the obtained low-dimensional nano-sized zeolites maintained the original dimension of nano-clays. As a result, the factors of inert materials, structure and morphology of clay, synthesis parameters, and so on, are studied as well as the crystallization mechanism for the in situ conversion of clay into zeolites in the confined space. In addition, the structure-activity relationship of low-dimensional nano-sized zeolite catalysts are also investigated by probing the catalytic performance of the esterification reaction of hexanoic acid and benzyl alcohol and epoxidation of styrene catalyzed by the low-dimension nano-sized zeolite catalysts. Therefore, this project will not only improve the economic value of clay based on its unique low-dimensional structure, but also propose a cheap synthetic route for preparing low-dimensional nano-sized zeolites.

低维纳米沸石（纳米片或纤维）因其孔道长度极短且可触酸性位点显著增加而具有极高的催化性能。然而，现有低维纳米沸石的合成常需使用特殊模板剂，其合成条件繁琐且价格昂贵。本项目在申请人前期黏土合成ZSM-5沸石基础上，提出对层状黏土进行聚合物插层修饰，再将黏土片层原位晶化为沸石纳米片；或将黏土剥离为纳米片或纤维后采用惰性材料包覆，再将其原位晶化为沸石纳米片或纤维的研究思路。惰性材料的包覆或填充使得黏土片层或纤维限制在纳米空间，有利于其被转化为同一维度的沸石。研究惰性材料、黏土结构与形貌、合成条件等对低维纳米沸石制备的影响，揭示纳米黏土在限制空间内原位转化为沸石的晶化机理；并以己酸与苯甲醇的酯化反应或苯乙烯环氧化反应为探针反应，探讨低维纳米沸石催化剂的构效关系。该项目以黏土为模板和原料合成低维纳米沸石，不仅充分利用了天然黏土的结构特点，提升其价值，也为低维纳米沸石的制备提供一条新颖且廉价的合成路线。

低维纳米沸石（纳米片或纤维）因其孔道长度极短且可触酸性位点显著增加而具有极高的催化性能。然而，现有低维纳米沸石的合成常需使用特殊模板剂，其合成条件繁琐且价格昂贵。本项目对高岭土进行聚苯胺插层修饰，再将其片层原位晶化为MFI型沸石纳米片；或将高岭土、凹凸棒石黏土、埃洛石剥离为纳米片或纤维后采用惰性碳材料或聚苯胺包覆，再将其原位晶化为MFI型沸石纳米片或纤维。研究了惰性材料及包覆方式、黏土结构与形貌、合成条件等对低维纳米沸石制备的影响，揭示了纳米黏土在惰性材料限制空间内从晶核形成到原位生长转化为纳米沸石的晶化机理；并以己酸与苯甲醇的酯化反应或环己烷氧化反应为探针反应，探讨低维纳米沸石催化剂的构效关系。结果表明在惰性材料包裹限制下形成的纳米沸石纤维或纳米片，由于粒径小，其催化活性优于常规沸石；由于糠醇气相沉积碳化形成的碳层比苯胺原位聚合形成的聚苯胺层更易在材料表面分布均匀，因此形成的纳米沸石粒径更小。ZSM-5纳米纤维在后续的酯化反应中展示出更高的活性，对己酸和苯甲醇的酯化率可以达到82.7%，重复使用5次以上；TS-1纳米纤维对环己烷的转化率可以达到50.7%。该项目以黏土为模板和原料合成低维纳米沸石，充分利用了天然黏土的结构特点、形貌和组分，为低维纳米沸石的制备提供一条新颖且廉价的合成路线。