Mesoporous Aluminosilicate Molecular Sieves Research Articles

Spectroscopic study of heterogeneous nanocomposition systems based on benzophenone

Phosphorescence spectra of the benzophenone capsulated into the inner space of mesoporous aluminosilicate molecular sieves of the MCM-41 type (the diameter of channels is about 4nm) have been analyzed at the 4.2–200K temperature range. For the comparison phosphorescence spectra of the bare MCM-41 matrix, pure benzophenone (at the same temperature region) and of the benzophenone incorporated to the porous glass with 54nm pore diameter at T=40K have been obtained. Some important conclusions about the phase state of encapsulated molecules have been made and a possible mechanism of the interaction between the filler and matrix active centers located on the pore inner surface (of the Si–OH type) has also been suggested using results of the NIR spectra investigation of the benzophenone included in the porous glass.

Investigation of Coke Deposits on Al-MCM-41

Carbonaceous compounds deposited on aluminosilicate mesoporous molecular sieves of the MCM-41 type during conversion of cyclohexene at various temperatures were investigated using TGA; DRIFT, UV−vis, and 13C solid state NMR spectroscopies; and a sorption technique. The chemical composition of the deposits is not significantly affected by the Al content of Al-MCM-41 and depends mainly on the temperature and the duration of the reaction. At lower applied temperatures, both aliphatic and aromatic compounds are formed; they are relatively weakly bound to the surface of the material. After a longer reaction period, some deposits appear that are strongly bound to the surface. At higher temperatures, a fraction of the coke migrates out of the pores. Then, part of the coke (most likely aliphatics) desorbs and moves away, while the other part (presumably aromatics) adsorbs on the external surface of the sieve. The coke remaining both in the pores and on the external surface mostly forms multilayered polyaromatic s...

Steam-Stable MSU-S Aluminosilicate Mesostructures Assembled from Zeolite ZSM-5 and Zeolite Beta Seeds

The structural integrity of Al-MCM-41 and related mesoporous aluminosilicate molecular sieves has been significantly improved in recent years through direct assembly and postsynthesis treatment methods.[1] Nevertheless, the hydrothermal instability and mild acidity remain inferior to conventional zeolites and limit potential applications in petroleum refining and fine chemicals synthesis.[2] One might expect to improve both the stability and acidity of these materials if zeolite-like order could be introduced into the pore walls. One approach, first introduced by van Bekkum and co-workers,[3] is to transform the preassembled walls of Al-MCM-41 into zeolitic structures by post-assembly treatment with a microporous zeolite structure director, such as tetrapropylammonium cations. More recent studies have shown that the walls of the mesostructure can indeed be converted to a zeolitic product, but the microporous zeolite phase (ZSM-5) is segregated from the mesostructure, giving rise to ZSM-5/ MCM-41 composites.[4] These composites exhibited an enhancement in acidity for hydrocarbon cracking in comparison to mechanical mixtures of ZSM-5 and MCM-41 and an improvement in steam stability for purely siliceous composites.[4c] We recently reported an alternative approach to more acidic and hydrothermally stable mesostructures based on the direct assembly of nanoclustered aluminosilicate precursors that normally nucleate zeolite type Y crystallization.[5] These protozeolitic species, known as azeolite seedso, promote zeolite nucleation by adopting AlO4 and SiO4 connectivities that resemble the secondary building units of a crystalline zeolite.[6] The assembly of the Na‡-nucleated zeolite type Y (faujasitic) seeds under hydrothermal conditions in the presence of cetyltrimethylammonium ions afforded hexagonal MSU-S mesostructures with Si/Al ratios in the range 1.6:1 to 10:1. The replacement of Na‡ by NH4‡ ions in the as-made mesostructure, followed by calcination in the presence of the surfactant, afforded exceptionally acidic and steam-stable mesostructures. However, the steam stability was enhanced by structure-stabilizing occlusions of carbon that formed during the calcination process. That is, the steam stability at 800 8C was in part a consequence of the exceptional acidity of a framework that formed structure-stabilizing carbon, and not entirely a result of an intrinsically stable framework. Here we also make use of protozeolitic nanoclusters to form exceptionally acidic and steam-stable aluminosilicate dichloromethane (10/1). Phosphirene complex 4 was isolated as yellow crystals (2 g, 66 %). 31P NMR (81 MHz, CDCl3): dˆy201.0 (1J(P,W)ˆ 294.9 Hz); 13C NMR (50 MHz, CDCl3): dˆ 89.3 (d, 1J(C,P)ˆ 18.8 Hz; P-C C), 93.9 (d, 2J(C,P)ˆ 5.8 Hz; P-C C), 120.9 (s; C C-Ph, Cipso), 195.9 (d, 2J(C,P)ˆ 9.1 Hz; cis-CO), 198.4 (d, 2J(C,P)ˆ 34.8 Hz; trans-CO); MS: m/z (%): 634 (6) [M‡], 494 (100) [M‡y 5 CO]; elemental analysis (%) calcd for C27H15O5PW: C 51.10, H 2.36; found: C 51.48, H, 2.42. 6 : Biphosphirene 6 was isolated as light yellow crystals by chromatography with hexane/dichloromethane (4/1). 13C NMR (50 MHz, CDCl3): dˆ 137.4 (d, 1J(C,P)ˆ 5.4 Hz; Cipso, Ph-P), 143.2 (pseudo t, 1J(C,P) 2J(C,P)ˆ 13.6 Hz; Ph-C(P)ˆC-P); MS: highest mass 785 [M‡y 10 COyH].

Several factors affecting Al-MCM-41 synthesis

Several mesoporous aluminosilicate molecular sieves with the MCM-41 structure (Si/Al=24) have been synthesized using different aluminum and silica sources and varying several synthesis parameters during the preparation process such as the use of an anti-foaming agent, prior aging of the gel mixture or pH adjustment of the gel mixture under basic conditions followed by autoclaving three times. All samples were characterized by X-ray diffraction (XRD), N 2 physisorption, TGA, 27 Al MAS NMR and elemental analysis. There is a significant improvement in the structure by using an anti-foaming agent before adding the surfactant, by aging the mixture of silica and aluminum source prior to synthesis, and by using δ-alumina instead of PHF alumina. Also, when the sample is synthesized, alternating the pH adjustment and autoclaving three times in sequence, well-resolved XRD peaks are obtained. These Al-MCM-41 materials have BET areas around 1000 m 2/g but the amount of tetrahedral coordinated Al, on the whole, is low.

Interactions in the Nitrobenzene–Molecular Sieves System

Implantation of nitrobenzene into the inner space of aluminosilicate mesoporous molecular sieves of the MSM–41 type was investigated. The interaction of nitrobenzene with the active centers of the inner surface of channels was studied by the method of IR spectroscopy. It was hypothesized that the possible mechanism of this interaction is the formation of hydrogen bonds of the –NO2...HO–Al(Si) type.

Influence of Confinement on The Phase Transition And Spectral Characteristics of Nematic Liquid Crystals

The results of nematic liquid crystal - isotropic liquid phase transition study by the method of differential scanning calorimetry for inclusion compounds - mesoporous aluminosilicate molecular sieves of MCM-41 type (including Cu-exchanged samples) with encapsulated in inner-crystalline space nematic liquid crystal (5CB), as well as IR spectroscopic data for such compounds were represented. It was shown, that the 5CB molecules are able to interact with the active centers in the MCM-41 channels forming strong enough bonds of -C≡N⋅⋅⋅H-O- type. The relative amount of 5CB molecules interacting with the walls of channels and those retaining ‘liquid crystalline’ state in binary systems of molecular sieves MCM-41 and CuMCM-41 was estimated. This conclusion was confirmed by the data obtained from differential scanning calorimetry measurements.

Mesoporous molecular sieve MCM-41 supported Co–Mo catalyst for hydrodesulfurization of dibenzothiophene in distillate fuels

A mesoporous aluminosilicate molecular sieve with MCM-41 type structure was synthesized using aluminum isopropoxide as the Al source. Supported Co–Mo/MCM-41 catalysts were prepared by co-impregnation of Co(NO 3) 2·6H 2O and (NH 4) 6Mo 7O 24 followed by calcination and sulfidation. For comparison, conventional Al 2O 3-supported sulfided Co–Mo catalysts were also prepared using the same procedure. These two types of catalysts were examined at two different metal loading levels in hydrodesulfurization of a model fuel containing 3.5 wt% sulfur as dibenzothiophene in n-tridecane. At 350–375°C under higher H 2 pressure (6.9 MPa), sulfided Co–Mo/MCM-41 catalysts show higher hydrogenation and hydrocracking activities at both normal and high metal loading levels, whereas Co–Mo/Al 2O 3 catalysts show higher selectivity to desulfurization. Co–Mo/MCM-41 catalyst at high metal loading level is substantially more active than the Co–Mo/Al 2O 3 catalysts.

Grafting of Al onto purely siliceous mesoporous molecular sieves

Aluminosilicate mesoporous molecular sieves exhibiting excellent structural ordering and enhanced acidity and catalytic activity have been prepared by reacting purely siliceous materials with Al-alkoxide in non-aqueous media. The Al is inserted into the framework of the purely siliceous parent material (MCM-41 or MMS) to generate (Brønsted) acid sites whose content is higher than in equivalent Al-MCM-41 materials prepared via the conventional direct mixed-gel synthesis method. 27Al MAS NMR and XPS confirm that the Al is incorporated into the solid framework where it adopts 4-coordinate symmetry. Bulk structural characterisation (using XRD and BET) shows that the hexagonal structure of the parent purely siliceous material is maintained during the grafting procedure with no loss of long range structural ordering. The resulting Al-grafted materials possess considerable catalytic activity for Brønsted acid catalysed cracking of cumene.

ChemInform Abstract: Aluminosilicate Mesoporous Molecular Sieves with Enhanced Stability Obtained by Reacting MCM‐41 with Aluminum Chlorohydrate.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Manganese−Bipyridine Complex Incorporated into Mesoporous MCM-41 Molecular Sieves

Siliceous (SiMCM-41) and aluminosilicate mesoporous molecular sieves (AlMCM-41) with variable framework Si/Al ratios have been used as supports to immobilize manganese 2,2‘-bipyridine (L) complex c...

Aluminosilicate Mesoporous Molecular Sieve MCM-48

Mesoporous aluminosilicate molecular sieves with the MCM-48 structure and atomic Si/Al ratios of 15−40 have been synthesized using aluminum chloride hexahydrate and aluminum sulfate as the sources ...

Aluminosilicate mesoporous molecular sieves with enhanced stability obtained by reacting MCM-41 with aluminium chlorohydrate

Aluminosilicate MCM-41 materials prepared by post-synthesis alumination using aqueous aluminium chlorohydrate exhibit remarkably high mechanical and hydrothermal stability and in addition the materials, after steaming at high temperatures, possess stronger Bronsted acid sites compared to the parent material.

The influence of template extraction on the properties of primary amine templated aluminosilicate mesoporous molecular sieves

Aluminosilicate mesoporous molecular sieves (Al-MMS) prepared at room temperature using hexadecylamine as template have been subjected to template extraction prior to calcination. Extraction in ethanol alone removes only that part of the template (in neutral form) which is not associated with framework Al while the presence of a cation (Na + or NH4 + ) ensures total template removal. Template extraction has no effect on elemental composition and for dry (non-calcined) samples results in an improvement in structural ordering. The effect of calcination depends on the mode of extraction; samples extracted in ethanol or ethanol/NH4 + are structurally stable to calcination and possess surface area and pore volume similar to directly calcined samples while ethanol/Na + extracted samples are relatively unstable and undergo considerable structural degradation resulting in lower surface area and pore volume. Dealumination results from calcination of amine or ammonium ion containing samples while Na containing samples do not undergo any dealumination. The acid content of calcined ethanol and ethanol/NH 4 + extracted samples is comparable to that of the directly calcined samples but the extracted samples exhibit higher catalytic activity for the cracking of cumene. Calcined ethanol/Na extracted samples possess very low acidity and exhibit no catalytic activity.

Novel isomerization of ω-phenylalkanals to phenyl alkyl ketones over cesium (lanthanum) oxide supported on mesoporous aluminosilicate molecular sieves and related materials

A novel rearrangement of the ω-phenylalkanals phenylacetaldehyde, 3-phenylpropionaldehyde and 4-phenylbutyraldehyde towards phenyl alkyl ketones is reported. The liquid-phase isomerizations are catalyzed by cesium oxide or binary cesium-lanthanum oxide supported on the mesoporous aluminosilicate molecular sieves MCM-41 and HMS and on amorphous supports like silica-alumina and γ-alumina. Beside the title reaction the aldol condensation is observed as a side-reaction. A mechanism is proposed in which the aromatic ring is involved in the rearrangement process. Factors governing the activities and product selectivities are presented.

N-heptane hydroconversion over aluminosilicate mesoporous molecular sieves

Aluminosilicate mesoporous molecular sieves (designated Al-MMS) have been prepared at room temperature using the primary amine hexadecylamine as organic templating surfactant. The materials have textural properties typical of mesoporous materials with short-range hexagonal order but exhibit higher Bronsted acidity compared to aluminium-containing MCM-41. The Pt-impregnated materials are efficient catalysts for the hydroconversion of n-heptane. At low Si/Al ratio (≤ 10) the materials have total conversions and selectivity comparable to that of USY zeolite (Si/Al = 21) and in addition exhibit considerable cyclisation at temperatures above 350°C. Our catalytic results show that the Pt-impregnated Al-MMS samples attain a good balance between the metal and acidic functions and that activity and selectivity are dependent on the Bronsted acid content and consequently on the amount of tetrahedral aluminium in the catalysts. The amount of Pt (in the range 0.25-1 wt%) mainly affects the selectivity to cyclised products which increases with Pt content at the expense of cracking; total conversion and selectivity to isomers remain largely unaffected.

96/04966 Synthesis of mesoporous molecular sieves and their application for catalytic conversion of polycyclic aromatic hydrocarbons

Molecular sieves such as Y and ZSM-5 are widely used catalysts in acid-catalyzed reactions for the production of fuels, petrochemicals, and fine chemicals. Despite their enormous use as environmentally safe catalysts, they are limited to convert relatively small molecules as their pore size is restricted to micropore size range (usually 1.4 nm). However, with the growing demand of technologies for treating heavier feeds, as well as for synthesizing large molecules for producing commodities and fine chemicals, it is necessary to develop catalysts with wider pores. Recently, Mobil workers have reported a new series of mesoporous molecular sieves: MCM-41 is one of the members of this extensive family of mesoporous series possessing a hexagonal array of uniform mesopores. Many reports have since appeared on synthesis and characterization of these new materials. However, information on their catalytic activity is still very limited. The pore dimensions of these materials can be tailored (in the range of 1.5-10.0 nm or more) through the choice of surfactant and auxiliary chemicals as templates and the crystallization conditions in the synthesis procedure. The BET surface area of these materials is more than 1000 m{sup 2}/g with high sorption capacities of 0.7 cc/g and greater. Moreover, these materialsmore » can be synthesized in a large range of framework Si/Al ratios and therefore can develop acid sites of different strength. Hence, these new mesoporous aluminosilicate molecular sieves, Al-MCM-41, might open new possibilities in developing catalysts for processing large molecules.« less

Synthesis and Catalytic Applications of Novel Mesoporous Aluminosilicate Molecular Sieves

ABSTRACTThis paper reports on the synthesis of four series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different aluminum compounds were examined as Al source in the hydrothermal synthesis of the mesoporous aluminosilicates of MCM-41 type, including pseudo boehmite (alumina), aluminum sulfate, aluminum isopropoxide, and sodium aluminate. Each Al source was examined at three different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the dioo-spacings for the samples prepared with different Al sources: sodium aluminate > Al isopropoxide > Al sulfate > pseudo boehmite. Such differences reveal that Al incorporation in the framework increases in the following order: pseudo boehmite < Al sulfate < Al isopropoxide < sodium aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. 27Al NMR and 29Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and sodium aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. We also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.

Synthesis of mesoporous molecular sieves: influence of aluminum source on Al incorporation in MCM-41

Three series of mesoporous aluminosilicate molecular sieves, MCM-41, with various Si/Al ratios were synthesized using different aluminum sources (aluminum isopropoxide, pseudo boehmite and aluminum sulfate). XRD analysis, temperature programmed desorption ofn-butylamine,27Al and29Si MAS NMR, and catalytic alkylation test indicated that aluminum isopropoxide is a better source for incorporating aluminum in the framework of MCM-41 type molecular sieves with better crystallinity and acid characteristics.

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrOnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrOnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrOnsted acid sites and exhibits highest catalytic activity.

Acidity and catalytic activity of aluminosilicate mesoporous molecular sieves prepared using primary amines

Mesoporous molecular sieves with enhanced Bronsted acidity and catalytic activity are generated using a primary amine surfactant route; the acidity and catalytic activity of these materials are higher than those of equivalent aluminosilicate MCM-41.