Synthesis of a hierarchical micro/mesoporous structure by steam-assisted post-crystallization.-猫眼课题宝

DOI：

10.1002/chem.200901034

发表时间：

2009-12

期刊：

Chemistry

影响因子：

通讯作者：

中科院分区：

文献类型：

作者：

Jian Zhou;Zile Hua;Jianlin Shi;Qianjun He;Limin Guo;M. Ruan

沸石因其较高的水热稳定性和充足的催化活性位点而被广泛用作固体酸催化剂和吸附剂，广泛应用于炼油、分离和环境领域。 [1]然而，沸石催化剂由于其孔径较小（< 1.5 nm），常常会遇到反应物和产物在其通道系统中扩散缓慢的问题。[2, 3] 近年来，介孔铝硅酸盐由于其较大的孔径和较窄的孔径分布，作为非均相催化剂引起了越来越多的研究兴趣。[4, 5] 在许多情况下，具有大孔的介孔材料由于其在大分子反应中的可能应用而受到极大的青睐。其中，之前报道的三维介孔材料TUD-1[6]在催化应用方面比传统介孔材料具有许多优势，例如合成成本低、孔径可调、粗骨架和三维介孔结构等。然而，其非晶态壁以及由此导致的低水热稳定性和催化活性严重限制了其实际应用。迫切需要合成结合沸石的高稳定性和催化活性和介孔材料的大孔径优点的新材料。迄今为止，人们已经尝试了各种合成方法来制备微/介孔复合材料。[7-11]硬模板合成，特别是Jacobsen等人报道的纳米碳模板方法[12, 13]以及最近Tsapatsis等人报道的有序介孔碳方法[14]是获得微/介孔结构的最有效途径之一。皮纳瓦亚等人。等人使用沸石晶种作为框架构建单元，可以自组织成介孔基质，成功制备了强酸性且相对稳定的微/介孔复合材料。[15-19]通过后续水热处理以结构导向剂作为辅助模板的非晶介孔材料的重结晶是另一种可能的方法。[20-23]然而，在大多数情况下，要么有序获得了具有无定形骨架的介孔材料，其壁中含有沸石初级单元或具有无序介孔结构的纳米晶沸石颗粒团聚体。另一方面，由于由沸石晶种组装而成的微/介孔复合材料本质上不具有与纳米晶沸石类似的水热稳定性，如果应用长时间的水热过程，它们的孔壁很容易收缩。 [5]最近，Ryoo等人报道了一种有机-无机杂化表面活性剂方法[24]为多级微孔/介孔结构的合成提供了一条新的、简单的途径，而且该产品在各种反应中表现出极高的抗催化活性失活的能力。 [25]然而，他们用作表面活性剂的专门设计的两亲性有机硅烷却买不到。本文将常规蒸汽辅助条件下的后结晶工艺[26, 27]应用于前驱体TUD-1材料，得到了具有分级微/介孔结构的铝硅酸盐（c-TUD-1）。该新型产品具有高比表面积和大孔容，孔径可达10 nm左右，水热稳定性高。此外，它在涉及大分子的催化中表现出比无定形硅铝酸盐和传统 ZSM-5 显着更高的活性。合成后的 TUD-1、c-TUD-1 和 c-TUD-1-HTACHTUNGTRENNUNG (200)（c-TUD-1 之后...的 X 射线粉末衍射 (XRD) 图案

Zeolites are widely used as solid-acid catalysts and adsorbents in oil refining, separation, and environmental fields thanks to their high hydrothermal stability and sufficient catalytically active sites.[1] Nevertheless, zeolite catalysts often suffer from the slow diffusion of reactants and products in their channel systems, which is a result of their small pore size (< 1.5 nm).[2, 3] In recent years, mesoporous aluminosilicates have attracted increasing research interest as heterogeneous catalysts due to their larger pore size and narrow pore-size distribution.[4, 5] In many cases, mesoporous materials with large pores are greatly favored due to their possible applications in macromolecular reactions. Among them, the previously reported three-dimensional mesoporous material TUD-1 [6] has many advantages over conventional mesoporous materials for applications in catalysis, such as cost-effective synthesis, a large and tunable pore size, thick frameworks, and a three-dimensional mesoporous structure. However, its amorphous walls and, consequently, low hydrothermal stability and catalytic activity have seriously limited its practical applications. Synthesis of new materials that combine the advantages of the high stability and catalytic activity of zeolites and the large pore size of mesoporous materials is highly desired. To date, various synthetic procedures have been attempted for the preparation of micro/mesoporous composites.[7–11] Hard template synthesis, especially the nanosized carbon template method reported by Jacobsen et al.[12, 13] and, very recently, the ordered mesoporous carbon method reported by Tsapatsis et al.,[14] is one of the most efficient routes to a micro/mesoporous structure. Pinnavaia etal. used zeolite seeds as framework building units that can self-organize into mesoporous matrices to successfully prepare strongly acidic and relatively stable micro/mesoporous composites.[15–19] Recrystallization of amorphous mesoporous materials with a structure-directing agent as a secondary template by subsequent hydrothermal treatment is another possible way.[20–23] In most cases, however, either ordered mesoporous materials with amorphous frameworks containing zeolitic primary units in the wall or agglomerates of nanocrystalline zeolite particles with a disordered mesoporous structure were obtained. On the other hand, because micro/mesoporous composites assembled from zeolite seeds are inherently not hydrothermally stable in a manner similar to that of nanocrystalline zeolites, their pore walls would easily shrink if a long hydrothermal process was applied.[5] Recently, an organic–inorganic hybrid surfactant method reported by Ryoo et al.[24] provided a new and simple route for the synthesis of hierarchical micro/mesoporous structure and, moreover, the product exhibited a remarkably high resistance to the deactivation of catalytic activity in various reactions.[25] However, the specially designed amphiphilic organosilane that they used as a surfactant is not available to buy.Herein, a post-crystallization process under conventional steam-assisted conditions [26, 27] was applied to precursor TUD-1 materials, and an aluminosilicate with hierarchical micro/mesoporous structure (c-TUD-1) was obtained. This novel product possesses high surface area and large pore volume, large pore size of around 10 nm, and high hydrothermal stability. Moreover, it demonstrates significantly higher activity than both amorphous aluminosilicate and conventional ZSM-5 in catalysis involving large molecules. X-ray powder diffraction (XRD) patterns of the as-synthesized TUD-1, c-TUD-1, and c-TUD-1-HTACHTUNGTRENNUNG (200)(c-TUD-1 after …

Synthesis of a hierarchical micro/mesoporous structure by steam-assisted post-crystallization.

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