Amphiphilic organosilane-directed synthesis of crystalline zeolite with tunable mesoporosity

Abstract

Zeolites are a family of crystalline aluminosilicate materials widely used as shape-selective catalysts, ion exchange materials, and adsorbents for organic compounds. In the present work, zeolites were synthesized by adding a rationally designed amphiphilic organosilane surfactant to conventional alkaline zeolite synthesis mixtures. The zeolite products were characterized by a complementary combination of X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The analyses show that the present method is suitable as a direct synthesis route to highly mesoporous zeolites. The mesopore diameters could be uniformly tailored, similar to ordered mesoporous silica with amorphous frameworks. The mesoporous zeolite exhibited a narrow, small-angle XRD peak, which is characteristic of the short-range correlation between mesopores, similar to disordered wormhole-like mesoporous materials. The XRD patterns and electron micrographs of the samples taken during crystallization clearly showed the evolution of the mesoporous structure concomitantly to the crystallization of zeolite frameworks. The synthesis of the crystalline aluminosilicate materials with tunable mesoporosity and strong acidity has potentially important technological implications for catalytic reactions of large molecules, whereas conventional mesoporous materials lack hydrothermal stability and acidity.

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

“…61 The second function, related to the hydrophobic part of the surfactant molecules, is to initiate the formation of organic domains between the inorganic fractions and thus, the surfactant can act as a mesoporogenic or spacer phase during crystallisation. This finally leads either to mesoporous zeolite crystals 61 or a layered assembly of zeolitic nanosheets. 76 For example, depending on the choice of the surfactant and targeted zeolite framework type, very thin zeolitic MFI-type nanosheets with intercrystalline mesopores were obtained in the presence of a specially designed diquarternary ammoniumtype surfactant.…”

“…76 For example, depending on the choice of the surfactant and targeted zeolite framework type, very thin zeolitic MFI-type nanosheets with intercrystalline mesopores were obtained in the presence of a specially designed diquarternary ammoniumtype surfactant. 61,76,77 In this approach (during the synthesis), the hydrophilic ammonium groups directed the formation of the microporous zeolite structure, whereas the hydrophobic surfactant chains were used to limit the further growth of the zeolite network along the b-direction. Thus, very thin zeolite layers were obtained (Fig.…”

Multimodal Zr-Silicalite-1 zeolite nanocrystal aggregates with interconnected hierarchically micro-meso-macroporous architecture and enhanced mass transport property

“…There have been many successful approaches to hierarchical MFI-type zeolites [16]. The synthetic techniques involve (i) chemical and/or physical posttreatment, such as the steaming or acid leaching methods [17][18][19]; (ii) hard templating synthesis, such as carbon and colloid templating [20][21][22]; (iii) soft templating synthesis, such as the use of amphiphilic organosilanes [23,24]. However, for increased efficiency within industrial processes, hierarchically porous zeolitic catalysts displaying both micro-meso-macroporosity and strongly active sites are more desirable.…”

Well‐Organized Zeolite Nanocrystal Aggregates with Interconnected Hierarchically Micro–Meso–Macropore Systems Showing Enhanced Catalytic Performance

“…Recently, various successful attempts to synthesize mesoporous or macroporous zeolites with bimodal porosity and framework acidity have been reported. [4][5][6][7][8][9][10][11][12][13][14][15] These materials hold great promise, particularly in catalysis and separation processes in which optimization of the diffusion and confinement regimes is required. Whereas micro-and/or mesopores provide size and shape selectivity for the guest molecules, and thus enhance the host-guest interactions, the presence of macropores can considerably favor diffusion of the guest molecules and thus their access to the active sites.…”