Understanding of the High Hydrothermal Stability of the Mesoporous Materials Prepared by the Assembly of Triblock Copolymer with Preformed Zeolite Precursors in Acidic Media

Highly active and spherical natured mesoporous aluminosilicate nanoparticles materialized for t-butylation of phenol

A green and recyclable AlSMSN material synthesised with enhanced hydrothermal stability has a rich tetrahedral Al ion coordination and reveals an unprecedented catalytic activity in t-butylation of phenol, among the other mesoporous catalysts.

High-Temperature Synthesis of Ordered Mesoporous Aluminosilicates from ZSM-5 Nanoseeds with Improved Acidic Properties

Ordered mesoporous SBA-15 analogs with different Si/Al ratios were successfully prepared in a two-step process from self-assembly of ZSM-5 nanoseeds at high temperature in mildly acidic media (473 K, pH 3.5). The obtained products were characterized as SAXS, XRD, N₂ sorption, FTIR, TEM, NH₃-TPD, AAS and ICP. The results show that the initial Si/Al molar ratio of ZSM-5 precursors strongly affects the final materials' properties. A highly condensed, well-ordered mesoporous SBA-15 analog with improved hydrothermal stability and acidic properties can be prepared from low aluminum containing ZSM-5 precursors (Si/Al ≥ 20). Reducing the initial Si/Al molar ratio to 10, however, leads to the formation of a disordered mesoporous SBA-15 type material accompanied by degraded textural and acidic properties. The gas phase cracking of cumene, carried out as probe reaction to evaluate Brønsted acidity, reveals that an increased density of Brønsted acid sites has been achieved over the SBA-15 analogs compared to conventional Al-SBA-15 due to the preservation of zeolite building units in the mesopore walls of the SBA-15 analogs.

Recent developments in liquid-phase selective oxidation using environmentally benign oxidants and mesoporous metal silicates

This Perspective article surveys recent advances in the synthesis of mesoporous transition-metal-containing silicate materials and their use for the liquid-phase selective oxidation of organic compounds with environmentally friendly oxidants – molecular oxygen, hydrogen peroxide and organic hydroperoxides.

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.

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.

Synthesis and catalytic applications of combined zeolitic/mesoporous materials

In the last decade, research concerning nanoporous siliceous materials has been focused on mesoporous materials with intrinsic zeolitic features. These materials are thought to be superior, because they are able to combine (i) the enhanced diffusion and accessibility for larger molecules and viscous fluids typical of mesoporous materials with (ii) the remarkable stability, catalytic activity and selectivity of zeolites. This review gives an overview of the state of the art concerning combined zeolitic/mesoporous materials. Focus is put on the synthesis and the applications of the combined zeolitic/mesoporous materials. The different synthesis approaches and formation mechanisms leading to these materials are comprehensively discussed and compared. Moreover, Ti-containing nanoporous materials as redox catalysts are discussed to illustrate a potential implementation of combined zeolitic/mesoporous materials.

Structure and colloidal stability of nanosized zeolite beta precursors

We report the mechanism of zeolite beta nucleation and growth at 120 degrees C in Al-containing solutions. Two solutions with molar compositions 1 SiO(2)/80 H(2)O/0.25 TEA(2)O/4 CH(3)CH(2)OH/(0.05 + Y) Na(2)O/Y Al(2)O(3), where Y is 0 and 0.01, were studied using attenuated total reflectance-Fourier transform spectroscopy, small angle scattering, and cryogenic-transmission electron microscopy. First, at room temperature, supersaturated silica self-assembles into primary particles (<3 nm). Upon heating the primary particles, the least stable ones aggregate into secondary particles. Some of the secondary particles are stable as spheroidal monomer particles, but others are unstable and aggregate into small clusters. After 4 days of heating, secondary particles are mostly composed of amorphous silica, but their density is similar to that of zeolite beta. All-silica secondary particles are stable in solution for extended periods of time (>100 days), and no all-silica zeolite beta product was obtained. On the other hand, after 6 days of heating solutions containing Al, we observe that Al-containing secondary particles aggregate into tertiary particles that have the structure of zeolite beta. We conclude that as silica reorganizes from amorphous into zeolite beta, Al-containing secondary particles become less stable (in the colloidal sense) and aggregate with tertiary particles.

Direct Synthesis of Well-Ordered and Unusually Reactive MnSBA-15 Mesoporous Molecular Sieves with High Manganese Content

The mesoporous MnSBA-15 materials with different n(Si)/n(Mn) ratios of 4, 8, 20, and 50 have been synthesized, for the first time, using manganese nitrate tetrahydrate and Pluronic 123 triblock polymer [(EO)20(PO)70(EO)20] by simply adjusting the molar ratio of water to hydrochloric acid (n(H2O)/n(HCl)) under direct hydrothermal conditions. For the effect of structural and textural properties with incorporation of manganese, the MnSBA-15 has been synthesized with different synthesis temperatures at the fixed molar ratios of n(Si)/n(Mn) = 4 and n(H2O)/n(HCl) = 295 in the synthesis gel. The hydrothermal and thermal stabilities of MnSBA-15 have also been investigated. The calcined MnSBA-15 materials prepared have been characterized by ICP-AES, XRD, N2 adsorption, ESR, FE-SEM, and TEM. The ICP-AES studies show a higher amount of manganese incorporation on the silica pore walls, as MnSBA-15 with a n(Si)/n(Mn) ratio up to 2.2 can be successfully prepared at a fixed n(H2O)/n(HCl) molar ratio of 295 by adjusting the ratios of n(Si)/n(Mn) in the synthesis gel. The structural and textural properties of calcined MnSBA-15 prepared can be found by the results of XRD and N2 adsorption. The investigation of ESR results clearly describe the effect of structure and Mn species coordination on the SBA-15 silica pore walls while the uniform pore diameter and rope-like hexagonal mesoporous structure of MnSBA-15 can be identified by TEM and FE-SEM images. With increasing synthesis temperature, an increase the unit cell parameter, pore size, and pore volume and a decrease the specific surface area and pore wall thickness of MnSBA-15 can be obviously noted by the results of XRD and N2 adsorption. The hexagonal MnSBA-15 materials prepared could be tested as catalysts in epoxidation of trans-stilbene to produce trans-stilbene oxide under various optimal conditions while their catalytic properties could also be compared to the results of MnMCM-41 and ZrMnMCM-41.

Highly Acidic Mesostructured Aluminosilicates Assembled from Surfactant-Mediated Zeolite Hydrolysis Products

The surfactant-mediated hydrolysis of ZSM-5 zeolite affords five-membered ring subunits that can be readily incorporated into the framework walls of a hexagonal mesostructured aluminosilicate, denoted MSU-Z. The five-membered ring subunits, which are identifiable by infrared spectroscopy, impart unprecedented acidity to the mesostructure, as judged by cumene cracking activity at 300 degrees C. Most notably, MSU-Z aluminosilicate made through the base hydrolysis of ZSM-5 in the presence of cetyltrimethylammonium ions exhibits a cumene conversion of 73%, which is 6.7-fold higher than the conversion provided by a conventional MCM-41. This approach to stabilizing zeolitic subunits through surfactant-mediated hydrolysis of zeolites appears to be general. The hydrolysis of USY zeolite under analogous hydrolytic conditions also affords zeolitic fragments that boost the acidity of the mesostructure in comparison to equivalent compositions prepared from conventional aluminosilicate precursors.