Mesopore-modified zeolites: preparation, characterization, and applications.

The application of templating methods to produce zeolite materials with hierarchical bi- or trimodal pore size distributions is reviewed with emphasis on mesoporous materials. Hierarchical zeolite materials are categorized into three distinctly different types of materials: hierarchical zeolite crystals, nanosized zeolite crystals, and supported zeolite crystals. For the pure zeolite materials in the first two categories, the additional meso- or macroporosity can be classified as being either intracrystalline or intercrystalline, whereas for supported zeolite materials, the additional porosity originates almost exclusively from the support material. The methods for introducing mesopores into zeolite materials are discussed and categorized. In general, mesopores can be templated in zeolite materials by use of solid templating, supramolecular templating, or indirect templating. In this categorization of templating methods, the nature of the interface between the zeolite crystal and the mesopore exactly when...

Templating mesoporous zeolites

With the necessity for the refining industry to treat heavier feedstocks, there is a clear demand for improved zeolite materials displaying better accessible surface areas and higher pore volumes in order to capitalize on their effectiveness. To this end, over the last decade, there has been an intensification of research on the exploration of new routes to synthesize zeolite materials combining micropores with mesopores. Different synthesis strategies are used for their preparation (i.e., by structure breaking or so-called ‘destructive’ pathways, or structure building or so-called ‘constructive’ synthesis pathways). This Review discusses the variety of current synthesis strategies, while emphasizing the strengths and weaknesses of the different routes regarding material characteristics; health, safety, and environment aspects; and synthesis costs.

Overview and Industrial Assessment of Synthesis Strategies towards Zeolites with Mesopores

Hierarchical zeolites combine the intrinsic catalytic properties of microporous zeolites and the enhanced access and transport of the additional meso- and/or macroporous system. These materials are the most desirable catalysts and sorbents for industry and become a highly evolving field of important current interests. In addition to the enhanced mass transfer leading to high activity, selectivity, and cycle time, another essential merit of the hierarchical structure in zeolite materials is that it can significantly improve the utilization effectiveness of zeolite materials resulting in the minimum energy, time, and raw materials consumption. Substantial progress has been made in the synthesis, characterization, and application of hierarchical zeolites. Herein, we provide an overview of recent achievements in the field, highlighting the significant progress in the past decade on the development of novel and remarkable strategies to create an additional pore system in zeolites. The most innovative synthesis approaches are reviewed according to the principle, versatility, effectiveness, and degree of reality while establishing a firm link between the preparation route and the resultant hierarchical pore quality in zeolites. Zeolites with different hierarchically porous structures, i.e., micro-mesoporous structure, micro-macroporous structure, and micro-meso-macroporous structure, are then analyzed in detail with concrete examples to illustrate their benefits and their fabrications. The significantly improved performances in catalytic, environmental, and biological applications resulting from enhanced mass transport properties are discussed through a series of representative cases. In the concluding part, we envision the emergence of "material-properties-by-quantitative and real rational design" based on the "generalized Murray's Law" that enables the predictable and controlled productions of bioinspired hierarchically structured zeolites. This Review is expected to attract important interests from catalysis, separation, environment, advanced materials, and chemical engineering fields as well as biomedicine for artificial organ and drug delivery systems.

Hierarchically Structured Zeolites: From Design to Application.

In this study an amorphous silica-alumina could be prepared using a carboxylic acid and its reactivity for the catalytic cracking was investigated. Malic acid (MA) was used as a catalyst for the sol–gel method, as an organic template and as a reagent for the dispersion of Al. When the ratio of MA/TEOS (tetraethoxysilane) increased from 0.22 to 1.22, the surface area, pore volume and pore diameter increased and the mesopore was formed at 1.22. The average BET pore diameters for 0.22 and 1.22 of MA/TEOS were 2.0–5.1 nm, respectively. With the single use of amorphous silica-alumina, conversions of n-dodecane were around 20% or less. With the single use of beta-zeolite, in contrast, the conversion to liquid and gas products reached 84%. In order to investigate the reactivity of amorphous silica-alumina as a matrix, we prepared the mixed catalysts which consist of 25% of zeolite, 56% of amorphous silica-alumina and 19% of binder (alumina sol) and we traced the activities for the catalytic cracking of n-dodecane. The average pore diameters were retained after zeolite was included. The product distribution changed compared with the single use of zeolite or silica-alumina and the comparable activity to that of zeolite was obtained although the mixed catalysts included only 25% of zeolite. Further, the amorphous silica-alumina with mesopores (MA122-5) exhibited the higher ratio of multi-branched paraffin to single branched paraffin in the gasoline franction of products (C5–C11) than the amorphous silica-alumina with only micropore or silica with mesopore or single zeolite.

Catalytic properties of amorphous silica-alumina prepared using malic acid as a matrix in catalytic cracking of n-dodecane

This paper presents the synthesis of mesoporous aluminosilicates from a hybrid organic-inorganic xerogel, using the chitosan biopolymer together with a hydrothermal treatment process as structural modeling tools. The properties of the material obtained point to an important role of the chitosan as a stabilizer of the structural lattice.

Stable Zeolite-Containing Mesoporous Aluminosilicates

The catalytic properties of zeolites can be improved in principle by anchoring them to mesoporous aluminosilicate networks that should allow diffusion of the species of interest towards the active sites. In this work the formation of composites between commercial zeolites and a sol precursory of aluminosilicates was studied in order to obtain this type of material.

E. Wolf

Papers

Stable Zeolite-Containing Mesoporous Aluminosilicates

Aluminosilicates of Bimodal Porosity Prepared by Hydrothermal Treatment Starting from Hybrid Composites