Synthesis, Stability and State of Boron in Boron-Substituted MCM-41 Mesoporous Molecular Sieves

On, D. Trong; Joshi, P.N.; Kaliaguine, Serge

doi:10.1021/jp953516r

Cited by 61 publications

(25 citation statements)

References 27 publications

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“…A typical synthesis procedure was described earlier (11,12 The homogeneous gel was transferred into a Teflon-lined autoclave and heated to 423 K for 48 h. The solid products were filtered, washed with distilled water, dried in air at 353 K, and finally calcined in flowing air at 813 K for 6 h (heated from room temperature to 813 K at the heating rate of 1 K/min). The pure-silica MCM-41 was synthesized using the same procedure, except that no boron was added.…”

Section: B-mcm-41mentioning

confidence: 99%

“…By comparison with zeolites, this material opens new possibilities for processing large molecules. Moreover, its acid properties can be modified by the substitution of silicon with boron (11,12). Therefore, taking into account both its very mild Brønsted acidity and large pore opening, B-MCM-41 has been tested as catalyst for the Prins condensation of formaldehyde with isobutylene.…”

Section: Prins Condensation Over H-b Mcm-41mentioning

confidence: 99%

“…13, a smoothly decreasing conversion is obtained as temperature is raised. It is believed that this minor decrease is due to partial hydrolysis of some Si-O-B bridges under the influence of the water vapor generated by the reaction (11,12).…”

Section: Prins Condensation Over H-b Mcm-41mentioning

confidence: 99%

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Isoprene by Prins Condensation over Acidic Molecular Sieves

Dumitriu

Kaliaguine

1997

Journal of Catalysis

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Section: B-mcm-41mentioning

confidence: 99%

Section: Prins Condensation Over H-b Mcm-41mentioning

confidence: 99%

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Isoprene by Prins Condensation over Acidic Molecular Sieves

Dumitriu

Kaliaguine

1997

Journal of Catalysis

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“…The increase in micropore volume suggests that nanoparticles of this zeolite have grown within the mesopore walls. Furthermore, the [5]UL-ZSM-5 sample shows an FT-infrared (IR) absorption band at 561/547 cm À1 (doublet) which is not present in the mesoporous precursor (the FT-IR spectra are not shown). Concomitantly, the micropore surface area (S micropore ) increases from 120 to 435 m 2 g À1 for this series of samples (Table 1).…”

mentioning

confidence: 99%

“…This indicates some modification of the tubular channels of these materials during crystallization. Figures 5 A and 5 B show bright-and dark-field TEM images recorded on the same area of [5]UL-ZSM-5, the bright spots in the image correspond to ZSM-5 nanocrystals. The mesoporous precursor with amorphous walls (Figure 3 a) provides a starting material from which nano-crystalline domains can nucleate within the walls.…”

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confidence: 99%

Large-Pore Mesoporous Materials with Semi-Crystalline Zeolitic Frameworks

Kaliaguine

2001

Angew. Chem.

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Mesoporous molecular sieves with well-defined pore diameters of 20 ± 500 [1±3] overcome the pore diameter constraint of zeolites (`10 ) [4] and allow the diffusion of larger molecules. Furthermore, high surface area and tunable pore size are among the many desirable properties that have made such materials the focus of great interest. However, these materials do not show short-range order and, from this point of view, are closer to amorphous than zeolitic materials. As a consequence, the mesoporous silica ± alumina have sites that are less acidic than those of zeolites, and do not exhibit the spectacular catalytic properties of acidic zeolites. Moreover, their hydrothermal stability is low and their industrial use as catalysts is rather limited to date. [1±3, 5, 6] Therefore, to upgrade the performances of mesoporous molecular sieves and zeolites, attempts have been made to synthesize a new type of material, which would combine the advantages of these two kinds of molecular sieves. To date, only a few articles concerning this study have been published. [7±12] For example, Kloetstra et al. [7] prepared MCM-41/FAU composites which gave a clear improvement in catalytic activity in the cracking of vacuum gasoil. Huang et al. [9] reported the synthesis of an MCM-41/ZSM-5 composite containing an interconnected mesopore and micropore structure. Attempts to crystallize the mesopore walls of mesostructured materials resulted in the formation of materials with increased thermal stability and catalytic activity. [10±14] A synthesis of a partially crystalline bimodal pore system with combined micro-and mesopores, for example, ITQ, has been achieved by delaminating the layered zeolite MCM-22 and ferrierite (FER). [10] Entrapped unit cells of ZSM5 contained in Al-MCM-41 and Al-HMS were prepared by ion exchange of the mesoporous aluminosilicates with tetrapropylammonium cation (TPA ) as an MFI-structure directing agent and then digestion of the mesoporous materials in glycerol at 120 8C. [11] Pinnavaia and co-workers [12,17] and Zhang et al. [18] recently reported steamstable aluminosilicate mesostructures assembled from zeolitetype seeds such as zeolite Y, ZSM-5, and zeolite beta. In the latter cases, the X-ray diffraction (XRD) patterns did not show crystalline features. Evidence for the presence of zeolite units cells may however be provided by the acid catalytic activity of such materials toward cumene cracking. [11,12] Herein, we describe a new general method for the production of a new type of material with semi-crystalline zeolitic mesopore walls. This procedure involves a templated solid-state secondary crystallization of zeolites starting from the amorphous mesoporous materials of corresponding elemental composition. It is important that the walls of the amorphous mesoporous precursor material are as thick as possible. References [2, 3] provide methods for the preparation of mesoporous precursors that are useful in this context including the synthesis and characterization of the mesoporous materials with semi-cryst...

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Ultrastable and Highly Acidic, Zeolite-Coated Mesoporous Aluminosilicates

On¹,

Kaliaguine²

2002

Angew. Chem.

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The acidity and hydrothermal stability of mesoporous aluminosilicates (MesoAS) are relatively low compared to those of zeolites, which limits their potential applications as catalysts in petroleum refining and fine chemicals synthesis. [1±7] Much effort has therefore been undertaken to synthesize a new type of materials, which combines the advantages of both zeolites and mesoporous molecular sieves. One might expect to improve both the stability and acidity of these materials if zeolite-like order could be introduced into the mesopore walls. Recent advances showed that amorphous walls of the mesostructure could indeed be converted to a partially zeolitic product. [8±13] For example, MCM-41/MFI composites containing interconnected mesopores and micropores were prepared by using dual templates and exhibited enhanced acidity and steam stability compared to the corresponding MCM-41. [8,9] Furthermore, the use of zeolite seeds as precursors for the assembly of mesoporous aluminosilicates with high hydrothermal stability and acidity was reported by Pinnavaia et al. [10] A similar zeolite beta type of materials was also prepared in the presence of co-templates of tetraethylammonium hydroxide and cetyltrimethylammonium bromide. [11] Recent results from our group showed the preparation of a new type of materials with semicrystalline zeolitic mesopore walls based on a templated solid-state secondary crystallization of zeolites starting from the amorphous walls of SBA-15. Bright-and dark-field transmission electron microscope (TEM) images recorded on the same area of the sample indicated that nanocrystals were embedded in the continuous amorphous inorganic matrix to form semicrystalline wall structures while preserving the mesoporous structure. The resulting mesoporous materials had much stronger acidity than those of the corresponding amorphous alumosilicates and a much improved hydrothermal stability. [12] Herein, we describe a new approach for the production of unusual zeolite-coated mesoporous aluminosilicates (ZCMeso-AS) using diluted clear solutions containing primary zeolite units. Hydrothermally ultrastable and highly acidic ZCMeso-AS result owing to the nanocrystalline zeolitic nature of their pore wall surface. These features open new possibilities for using this type of materials as acid catalysts.It is of special concern that due to the size of primary ZSM-5 units templated by tetrapropylammonium ions (2.8 nm in diameter), [13±14] the pore diameter of the mesoporous precursor molecular sieves should be higher than 30 ä. The methods in references [2] and [3] are therefore useful in this context for the preparation of mesoporous precursors, such as SBA-15 and siliceous mesostructured cellular foams (MCFs).The N 2 adsorption/desorption isotherms obtained from the calcined sample before and after coating are shown in Figure 1 A. The parent and ZSM-5-coated samples display the typical behavior of a mesoporous molecular sieve with a mesopore volume saturation capacity of about 1.56 and 0.78 cm 3 g À1 , respectively...

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Synthesis, Stability and State of Boron in Boron-Substituted MCM-41 Mesoporous Molecular Sieves

Cited by 61 publications

References 27 publications

Isoprene by Prins Condensation over Acidic Molecular Sieves

Isoprene by Prins Condensation over Acidic Molecular Sieves

Large-Pore Mesoporous Materials with Semi-Crystalline Zeolitic Frameworks

Ultrastable and Highly Acidic, Zeolite-Coated Mesoporous Aluminosilicates

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