Mesoporous aluminosilicates with ordered hexagonal structure, strong acidity, and extraordinary hydrothermal stability at high temperatures

N-Methyl-2-pyrrolidone assisted synthesis of hierarchical ZSM-5 with house-of-cards-like structure

This work presents a facile, economic and green synthesis of highly active house-of-cards-like ZSM-5 by the addition of N-methyl-2-pyrrolidone (NMP) into a template-free zeolite synthesis system.

Porous materials in catalysis: challenges for mesoporous materials

The discovery of ordered mesoporous materials has opened great opportunities for new applications in heterogeneous catalysis, thanks to their hitherto unprecedented intrinsic structural features. Evidence shows that, however, these materials have not met the researchers' expectations mainly because of the severe limitations related to the strength of acid sites and to the thermal/hydrothermal stability, significantly lower than those of zeolites and due to the amorphous nature of the mesostructured materials. These features are highlighted in the first part of this review, where the peculiarities of mesostructured materials are compared with those of zeolite catalysts in some reactions of industrial interest. New synthesis strategies, especially designed for preparing materials with improved physico-chemical and textural properties, together with the catalytic features of the resulting materials, are described and discussed in the second part of the review.

One-pot synthesis of Aluminum-containing ordered mesoporous silica MCM-41 using coal fly ash for phosphate adsorption

The present study offers an economic one-pot synthesis of Al-containing ordered mesoporous silica MCM-41 from the coal fly ash. The samples were characterized by small-angle XRD, N2 adsorption, TEM, mapping, (27)Al MAS NMR, EDX, and NH3-TPD. The effects of pH values to the final mesostructures have also been investigated. The results show that the material prepared at the pH value of 10 displays the largest pore volume of 0.98 cm(3)/g, the highest BET surface area of 1020 m(2)/g, and the lowest Si/Al molar ratio of 2. Using this material as adsorbent for phosphates, the adsorption capacity reaches 64.2mg/g at 298 K, which is much higher than that of large pore mesoporous silica SBA-15 (53.5mg/g), diatomite (62.7 mg/g), and MCM-41 (31.1 mg/g). In addition, the thermodynamics and kinetics for the phosphate adsorption were also investigated. Our present study shows an economic way to treat phosphates using the industrial solid waste of coal fly ash.

Investigation on the effect of zeolite precursor on the formation process of MCM-41 containing zeolite Y building units

The formation process of MCM-41 containing zeolite Y building units has been investigated by UV Raman spectroscopy, (29)Si and (27)Al MAS NMR spectroscopy, X-ray diffraction (XRD), N2 adsorption and electron microscopy (SEM and TEM). It is found that the precursor containing zeolite Y secondary building units promotes the formation of a metastable mesopore structure just after mixing the zeolite precursors with CTAB. In contrast, the low-polymerized aluminosilicates and well-crystallized zeolite crystals cannot be assembled with CTAB at this stage. The result supports that the zeolite secondary building units should promote to the formation of the mesopore wall. This has been ascribed to its high anionic charge density as well as the appropriate multidentate coordination. Lowering down the pH value to 9.3 facilitates the further polymerization of the aluminosilicate species to build up a stable mesoporous phase.

Self-templating synthesis of hollow mesoporous silica and their applications in catalysis and drug delivery

Hollow mesoporous silica materials have been intensively pursued because of their unique properties for various applications. Yolk/shell structured hollow mesoporous silica with functional cores inside their hollow interior can further broaden the applications of hollow mesoporous silica. The self-templating strategy has been developed as one of the most important strategies to effectively fabricate hollow mesoporous silicas and their yolk/shell counterparts. In this feature article, we provide an overview of advances in the self-templating synthesis of hollow mesoporous silica based on the following three strategies: surface-protected etching, structural difference-based selective etching, and cationic surfactant assisted self-templating. We then discuss some important applications of these self-templating strategy-derived hollow mesoporous silicas, such as nanoreactors for confined catalysis and multifunctional platforms for combined therapy. Finally, some perspectives for the future development of this active research field are provided.

Hollow mesoporous aluminosilica spheres with perpendicular pore channels as catalytic nanoreactors

The design and synthesis of hollow/yolk-shell mesoporous structures with catalytically active ordered mesoporous shells can infuse new vitality into the applications of these attractive structures. In this study, we report that hollow/yolk-shell structures with catalytically active ordered mesoporous aluminosilica shells can be easily prepared by using silica spheres as the silica precursors. By simply treating with a hot alkaline solution in the presence of sodium aluminate (NaAlO(2)) and cetyltrimethylammonium bromide (CTAB), solid silica spheres can be directly converted into high-quality hollow mesoporous aluminosilica spheres with perpendicular pore channels. On the basis of the proposed formation mechanism of etching followed by co-assembly, the synthesis strategy developed in this work can be extended as a general strategy to prepare ordered mesoporous yolk-shell structures with diverse compositions and morphologies simply by replacing solid silica spheres with silica-coated nanocomposites. The reduction of 4-nitrophenol with yolk-shell structured Au@ordered mesoporous aluminosilica as the catalyst has clearly demonstrated that the highly permeable perpendicular pore channels of mesoporous aluminosilica can effectively prevent the catalytically active yolk from aggregating. Furthermore, with accessible acidity, the yolk-shell structured ordered mesoporous aluminosilica spheres containing Pd yolk exhibit high catalytic activity and recyclability in a one-pot two-step synthesis involving an acid catalysis and subsequent catalytic hydrogenation for desired benzimidazole derivative, which makes the proposed hollow ordered aluminosilica spheres a versatile and practicable scaffold for advanced catalytic nanoreactor systems.

Synthesis of hydrothermally stable, hierarchically mesoporous aluminosilicate Al-SBA-1 and their catalytic properties

Hydrothermally stable mesoporous aluminosilicates Al-SBA-1 with hierarchical pore structure have been successfully synthesized under alkaline condition at 120 °C by employing organic mesomorphous complexes of polyelectrolyte (poly(acrylic acid) (PAA)) and cationic surfactant (hexadecyl pyridinium chloride (CPC)) as template. The Si/Al ratio could be as high as 5 and the incorporation of Al into the silica framework did not disturb the well-ordered cubic Pm ̅3n mesostructure. Meanwhile, the incorporation of Al could greatly increase the specific surface area and pore volume of the samples. The Al-SBA-1 materials exhibited a high hydrothermal stability and remained stable even after being treated in boiling water for 10 days. The catalytic activity of the Al-SBA-1 materials was investigated by employing the Friedel-Crafts alkylation of toluene with benzyl alcohol as a model reaction and they exhibited excellent catalytic property due to the incorporated acid sites and the hierarchically mesoporous structure.

Directing zeolite structures into hierarchically nanoporous architectures

Crystalline mesoporous molecular sieves have long been sought as solid acid catalysts for organic reactions involving large molecules. We synthesized a series of mesoporous molecular sieves that possess crystalline microporous walls with zeolitelike frameworks, extending the application of zeolites to the mesoporous range of 2 to 50 nanometers. Hexagonally ordered or disordered mesopores are generated by surfactant aggregates, whereas multiple cationic moieties in the surfactant head groups direct the crystallization of microporous aluminosilicate frameworks. The wall thicknesses, framework topologies, and mesopore sizes can be controlled with different surfactants. The molecular sieves are highly active as catalysts for various acid-catalyzed reactions of bulky molecular substrates, compared with conventional zeolites and ordered mesoporous amorphous materials.

Redox active mesoporous hybrid materials by in situ syntheses with urea-linked triethoxysilylated phenothiazines

Triethoxysilyl functionalized phenothiazinyl ureas were synthesized and immobilized by in situ synthesis into mesoporous hybrid materials. The designed precursor molecules influence the structure of the final materials and the intermolecular distance of the phenothiazines. XRD and N(2) adsorption measurements indicate the presence of highly ordered two-dimensional hexagonally structured functional materials, while the incorporation of the organic compounds in the solid materials was proved by means of (13)C and (29)Si solid state NMR spectroscopy as well as by FT-IR spectroscopy. Upon oxidation with (NO)BF(4) or SbCl(5), stable phenothiazine radical cations were generated in the pores of the materials, which was detected by means of UV/Vis, emission, and EPR spectroscopies.

Improved synthesis and study of acidic properties of ‘plugs’-containing Al-SBA-15 materials

A novel ‘plugs’-containing Al-SBA-15 material (denoted as PAS) was directly synthesized through simultaneous introducing toluene and aluminum precursor into the reaction mixture of traditional SBA-15. Such material not only featured a unique two-step desorption isotherm as conventional plugged SBA-15 synthesized using excessive siliceous precursor, and higher pore wall thickness than that of other analogous materials, but also possessed weak and medium acidic sites, which implied the PAS would offer unusual advantages such as multifunctionality to process a large variety of feed-stocks in acid-involved reaction (e.g. polymerization of tetrahydrofuran) in industrial point of view. In addition, catalytic activity of the PAS was investigated by the tetrahydrofuran (THF) polymerization reaction in the presence of acetic anhydride and compared with Al-doped MCM-41 prepared via conventional direct hydrothermal synthesis. The PAS exhibited good performance on polymerization of THF. Such result could be related to the large pore size and moderate acidic sites.

Shaping colloidal rutile into thermally stable and porous mesoscopic titania balls

High crystallinity and controlled porosity are advantageous for many applications such as energy conversion and power generation. Despite many efforts in the last decades, the direct synthesis of organic-inorganic composite materials with crystalline transition metal oxides is still a major challenge. In general, molecules serve as inorganic precursors and heat treatment is required to convert as-synthesized amorphous composites to stable crystalline materials. Herein, an alternative approach to the direct synthesis of crystalline polymer-metal oxide composites by using a spherical polyelectrolyte brush as the template system is presented. Pre-synthesized electrostatically stabilized rutile nanocrystals that carry a positive surface charge are used as inorganic precursors. In this approach, the strong Coulomb interactions between anionic polyelectrolyte brush chains and cationic crystalline rutile colloids, whose surfaces are not capped and therefore reactive, are the key factors for the organic-inorganic crystalline composite formation. Stepwise calcination first under argon and followed with a second calcination in air lead to the complete removal of the polymer template without collapse and porous rutile balls are obtained. The results suggest that any colloids that carry a surface charge might serve as inorganic precursors when charged templates are used. It is expected that this hierarchical route for structuring oxides at the mesoscale is generally applicable.