Tailoring and visualizing the pore architecture of hierarchical zeolites

Abstract

Recently the concept of hierarchical zeolites invoked more explicit attention to enhanced accessibility of zeolites. By realizing additional meso-/macroporosity with the intrinsic microporosity of zeolites, a hierarchical pore system arises which facilitates mass transport while maintaining the zeolite shape selectivity. A great number of synthesis strategies have been developed for tailoring the pore architecture of hierarchical zeolites. In this review, we give a general overview of different synthesis methods for introduction of additional porosity. Advantages and limitations of these different synthesis approaches are addressed. The assessment of pore structure is essential to build the link between the zeolite pore structure and its functionality. A variety of 2D and 3D microscopy techniques are crucial to visualize the hierarchical pore structure, providing unique and comprehensive information that, however, should be linked to the results of bulk characterization techniques as much as possible. The microscopy techniques are classified and discussed according to the different probes used, such as optical light, X-rays and electrons. Representative work is reviewed to elucidate the capability of each technique and their drawbacks.

The Role of Non-Framework Lewis Acidic Al Species of Alkali-Treated HZSM-5 in Methanol Aromatization

“…The intrinsic mesoporosity of HZ listed in Table 1 should be attributed to slit-shaped intercrystalline void less than 4 nm wide. Hence, the employed alkaline treatment is effective in cultivating intercrystalline mesopores in a 10-20 nm range [11]. A close inspection showed that HZ-D had the mesopore size at 11.5 nm; HZ-DA, 18.7 nm.…”

“…Hierarchical ZSM-5 can be synthesized through a bottom-up (constructive) or a top-down (destructive) method: the former is to impede the crystal growth or to introduce a mesoporous template in the preparation; the latter is to extract/rearrange atoms of Si and Al (demetallation) from the framework [10,11]. By comparison, the destructive method using alkaline treatment (desilication) is more applicable, reliable, and cost-effective (e.g., this method does not use any expensive template as the bottom-up method does [10]) in large-scale production.…”

Catalytic Isomerization of Dihydroxyacetone to Lactic Acid and Alkyl Lactates over Hierarchical Zeolites Containing Tin

“…Recently, there has been a growing interest among scientists in the synthesis, characteristics and application of hierarchical zeolites [5][6][7][8]. These materials, characterized by occurrence of secondary porosity (mesopores) superimposed on the primary microporous structures, constitute a class of porous materials displaying molecular sieve capacity and mesoporous materials.…”

A Hierarchically Porous Carbon Fabric for Highly Sensitive Electrochemical Sensors

“…[18] The fabrication techniques have been used with silica or organic materials as hard templates impregnating with appropriate carbon precursor, followed by carbonization of the composite and the removal of template, [19] resulting in the ordered macro-and meso-structure. [20][21][22][23] Besides high active sites, the introduction of meso-pores into a micro-or macro-porous structure provides size and shape selectivity for reactants, intermediates, and products, thus hierarchically porous products have been widely used as catalysts [24,25] or catalyst supports, [26] separation process, [27] energy conversion, [28] and storage. [18,[29][30][31] However, unlike porous structures made of materials like metal, [32,33] polymer, [34] or silica, [35] the superhydrophilic property has been less utilized on the hierarchical porous carbon materials with conductive nature to improve the sensibility for electrochemical molecules.…”