Ordered mesoporous materials with MFI structured microporous walls - Synthesis and proof of wall microporosity
Ordered mesoporous materials with MFI structured microporous walls - Synthesis and proof of wall microporosity
复制标题
DOI：
10.1016/j.micromeso.2012.07.025
复制
发表时间：
2012-12
影响因子：
5.2
通讯作者：
M. Reichinger;W. Schmidt;Vaishali V. Narkhede;Weiping Zhang;H. Gies;W. Grünert
中科院分区：
文献类型：
--
作者：
M. Reichinger;W. Schmidt;Vaishali V. Narkhede;Weiping Zhang;H. Gies;W. Grünert
以MFI型分子筛（Silicalite-1，TS-1）为前驱体，采用软模板法合成了一维六方和三维立方对称的有序介孔材料（OSTO）。通过XRD、氮气和氩气物理吸附、DTG/DTA、IR、UV-vis光谱、XANES、TEM、119 NMR和对分布函数（PDF）的测定来表征产物，以阐明其结构，特别是证明在小于XRD的相干长度的阵列中，即在孔壁中存在微孔。物理吸附研究和TEM很好地支持了蒙脱石的中孔性，而XRD记录了结构的规则性，这也排除了微孔晶粒的存在。相反，微孔检测到四面体配位的Ti-网站（XANES）的吸附/解吸水，通过119 NMR，通过PDF与那些无定形和MFI型固体的比较，并通过顺序分解的结构导向剂的介观和介观系统。通过XRD和物理吸附数据的比较以及TEM显微照片，得出微孔中孔壁的厚度为约1.5nm。因此，Ar物理吸附检测MFI结构的典型尺寸的孔的失败归因于小的孔隙体积和非常短的孔延伸。水热后处理可以改善具有一维六方孔系统的OC 12的结构完整性，尽管它们的孔壁具有微孔性质，这导致更窄的中孔尺寸分布，在稍大的孔径处达到峰值。
Ordered mesoporous materials (OMMs) of 1-dimensional hexagonal and 3-dimensional cubic symmetry of the pore systems were synthesized via well-established soft templating routes starting from precursor solutions of MFI-type zeolites (Silicalite-1, TS-1). The products were characterized by XRD, nitrogen and argon physisorption, DTG/DTA, IR, UV–vis spectroscopy, XANES, TEM,119Xe NMR, and determination of the pair distribution function (PDF) in order to elucidate their structure, in particular to prove the presence of microporosity in arrays smaller than the coherence lengths of XRD, i.e. in the pore walls. The mesoporosity of the OMMs was well supported by physisorption studies and by TEM while the regularity of the structure was documented by XRD, which also served to exclude the presence of microporous crystalline grains. Instead, microporosity was detected by adsorption/desorption of water on tetrahedrally coordinated Ti-sites (XANES), by119Xe NMR, by the comparison of the PDF with those of amorphous and of MFI-type solids, and by sequential decomposition of the structure directing agents for meso and micropore systems. From comparison of XRD and physisorption data and from the TEM micrographs, the thickness of the microporous mesopore walls was concluded to be ≈1.5nm. Therefore, the failure of Ar physisorption to detect pores of sizes typical of MFI structures was attributed to the small micropore volume and the very short pore extension. The structural integrity of OMMs with 1-dimensional hexagonal pore system could be improved by a hydrothermal post-treatment despite the microporous nature of their pore walls, which resulted in more narrow mesopore size distributions peaking at somewhat larger pore sizes.