Nanometer scale precursors in the crystallization of Si-TPA-MFI

Moor, Peter-Paul E. A. de; Beelen, Theo P. M.; Komanschek, Bernd U.; Santen, Rutger A. van

doi:10.1016/s1387-1811(98)00008-0

Cited by 48 publications

(47 citation statements)

References 15 publications

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“…The evidence for this is also provided by IR spectroscopy. The spectrum of MTS-9 gives the band at 550 cm )1 which is characteristic of 5-rings of PSBU in TS-1 zeolite [51,52]. In contrast, we cannot detect this band with Ti-MCM-41.…”

Section: Hydrothermal Stable Mesoporous Titanosilicates With Catalyticontrasting

confidence: 59%

“…The aluminosilicate precursors appear to serve as seeds for the formation of Beta zeolite. IR characterization of these aluminosilicate precursors shows a clear band at 520-600 cm )1 , which is characteristic of 5-membered rings, indicating that aluminosilicate precursors contain zeolite primary and secondary structure building units [51,52]. Table 4 presents textural properties of MAS-5 prepared from preformed Beta zeolite precursors and conventional MCM-41.…”

Section: Strongly Acidic and Hydrothermally Stable Mesoporous Aluminomentioning

confidence: 99%

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Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Xiao

2005

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Microporous crystals of zeolites such as Y, Beta, and ZSM-5 are widely used commercial catalysts, but their applications are strongly limited by their small pore sizes. Recent progress in solving this is used to ordered mesoporous materials such as MCM-41, HMS, and SBA-15. These mesoporous materials have pore diameters of 2.0-30 nm and exhibit good catalytic properties for the catalytic conversion of bulky reactants. However, when compared with microporous crystals of zeolites, the catalytic activity and hydrothermal stability are relatively low, which severely hinders their practical applications in industrial catalytic reactions such as petroleum cracking. The relatively low catalytic activity and hydrothermal stability can be attributed to the amorphous nature of the mesoporous walls. In this account, we systemically review the routes for improving catalytic activity and hydrothermal stability of mesoporous materials, which include (1) acidic sulfated zirconia supported in mesoporous materials; (2) strongly acidic and thermally stable mesostructured sulfated zirconia with tetragonal crystalline phase; (3) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in alkaline media; (4) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in strongly acidic media; (5) hydrothermally stable mesoporous titanosilicates with catalytically active titanium species in oxidations; (6) high-temperature generalized synthesis of ultrastable ordered mesoporous silica-based materials by using fluorocarbonhydrocarbon surfactant mixtures.

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Section: Hydrothermal Stable Mesoporous Titanosilicates With Catalyticontrasting

confidence: 59%

Section: Strongly Acidic and Hydrothermally Stable Mesoporous Aluminomentioning

confidence: 99%

Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Xiao

2005

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“…In the industrial synthesis of silicas and silica-based materials, elevated temperatures are often required to produce the desired structure. Especially in the formation of crystalline products (the zeolites), temperature is important to start the nucleation reaction (van Bekkum et al 1991;de Moor et al 1997de Moor et al , 1998Biz and Ocelli 1998). In many other processes, higher temperatures (DT >80°C) are only applied to accelerate processing times, without changing equilibria or product properties considerably.…”

Section: Silica Synthesis In Diatomsmentioning

confidence: 99%

“…In diatoms the role of temperature is negligible, since diatoms are restricted to moderate temperature boundaries of the aquatic environment (about -2 to 30°C). Of course, temperature can be used very well to manipulate the reaction rate in in situ silica synthesis, e.g., to design conditions to study silica transformations over time (de Moor et al , 1998Sun et al 2002;Vrieling et al 2002). For time-resolved small angle X-ray (SAXS) analysis of (bio)polymer-silica particle formations, the concentration of silica can be as low as 1% (w/v) SiO 2 , resulting in polymerization at room temperature followed by a very slow aging of the silica.…”

Section: Silica Synthesis In Diatomsmentioning

confidence: 99%

Silicon Biomineralisation: Towards Mimicking Biogenic Silica Formation in Diatoms

Vrieling¹,

Hazelaar²,

Gieskes

et al. 2003

Silicon Biomineralization

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IntroductionSilica is by far the most abundant compound in the earth's crust. It serves various functions in nature: organisms ranging from lower eukaryotes to plants use it as one of the biominerals that provide support, protection, strength, or tools in various functions. Biogenic silica is the least studied of the biominerals. The best-studied ones (Hunter 1996) are composed of calcium (apatite, enamel, calcite); these are present in the bone tissue and teeth of mammals and in the shells of shellfish. In contrast to calcium minerals, relatively little is known about the formation of biogenic silica. The most likely function of biogenic silica in unicellular organisms seems to be giving strength to the living cell; good examples from the aquatic environment are siliceous (exo)skeletons or cell casings of the microalgal groups of diatoms ( Fig. 1) and silicoflagellates, and of Radiolaria (Simpson and Volcani 1981; Pickett-Heaps et al. 1990;Round et al. 1990).Silica and silica-based materials (e.g. zeolites and MCM-type materials) are also widely used in a variety of industrial and technological applications. A limited number of micro-and mesoporous silicas serve as fillers in rubber materials (e.g. in tyres), as catalyst supports, as drying agents, as abrasives (e.g. toothpastes), or as filters in separation technologies (Iler 1979;Brinker and Scherer 1990;Bergna 1994). A prerequisite for each application is that a silica with specific properties of mechanical strength, pore volume, pore-size distribution, or specific surface area is required. The current demand for "the best" silicas in these respects is increasing and a search for new, improved or alternative artificial silica materials has been going on for a few years. Biogenic silica sources also have received more attention lately (Morse 1999;Vrieling et al. 1999b). It is expected that if nature can be mimicked, a wide range of innovative and new tailor-made silicas can be produced approaching the variety in architecture seen in nature, e.g. in the algal class of diatoms (Vrieling et al.

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“…In situ X-ray scattering measurements have been carried out using synchrotron radiation to observe the crystallization of microporous materials under hydrothermal heating conditions. [5][6][7][8][9][10] In situ studies such as these enable direct observation of the gel formation and dissolution, nucleation, and growth processes of zeolites.…”

Section: Introductionmentioning

confidence: 99%

In Situ SAXS/WAXS of Zeolite Microwave Synthesis: NaY, NaA, and Beta Zeolites

et al. 2007

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A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.

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Nanometer scale precursors in the crystallization of Si-TPA-MFI

Cited by 48 publications

References 15 publications

Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Silicon Biomineralisation: Towards Mimicking Biogenic Silica Formation in Diatoms

In Situ SAXS/WAXS of Zeolite Microwave Synthesis: NaY, NaA, and Beta Zeolites

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