UV Raman spectroscopic study on the synthesis mechanism of zeolite X

The synthesis of zeolite X is characterized by UV Raman spectroscopy, NMR spectroscopy, and X-ray diffraction. UV Raman spectra of the liquid phase of the synthesis system indicate that AI(OH); species are incorporated into silicate species, and the polymeric silicate species are depolymerized into monomeric silicate species during the early stage of zeolite formation. An. intermediate species possessing Raman bands at 307, 503, 858 and 1020 cm(-1) is detected during the crystallization ill the solid phase transformation. The intermediate species is attributed to the beta cage, the secondary building unit of zeolite X. A model for the formation of zeolite X is proposed, which involves four-membered rings connecting to each other via six-membered ring to form beta cages, then the beta cages interconnect via double six-membered rings to form the framework of zeolite X. (C) 2001 Elsevier Science B.V. All rights reserved.

Characterization of aluminosilicate zeolites by UV Raman spectroscopy

A series of aluminosilicate zeolites are characterized by UV Raman spectroscopy for the first time, and UV Raman spectra of various zeolites give strong and clear bands with high resolution, while conventional Raman spectra of these zeolites are difficult to obtain because of a strong background fluorescence. Additionally, these zeolites show several new bands in UV Raman spectroscopy. A summary of these UV Raman spectra over various zeolites suggests that the bands at 470-530, 370-430, 290-410, and 220-280 cm(-1) can be assigned to the bending modes of 4-, 5-, 6-, and 8-membered rings of aluminosilicate zeolites, respectively. Furthermore, it is found that the band intensity of zeolites in UV Raman spectroscopy is dependent on the Si/Al ratio. Moreover, the UV Raman spectra of crystallization, for zeolite X at various times show that, in the initial stage of crystallization, the 4-membered rings (510 cm(-1)) interconnect each other to form beta -cages with 6-membered rings (390 cm(-1)), which further crystallize to zeolite X. (C) 2001 Elsevier Science B.V. All rights reserved.

Stable ordered mesoporous silica materials templated by high-temperature stable surfactant micelle in alkaline media

Ordered hexagonal mesoporous silica material (JLU-30) has been successfully synthesized in alkaline media at high temperature (> 160 degreesC, using cationic (1,3-dimethyl-2-imidazolidin-2-ylidene)hexadecylmethyl-ammonium bromide (DIHAB) as a template, and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, differential thermal analysis (DTA), and thermogravimetric analysis (TG), as well as Al-27 and Si-29 nuclear magnetic resonance (NMR) spectroscopy. Mesoporous JLU-30 shows much higher hydrothermal stability than MCM-41. Si-29 NMR spectra indicate that the pore walls of JLU-30 samples synthesized at high temperature (160 degreesC) are fully condensed, giving a Q(4)/Q(3) ratio as high as 6.2. In contrast, MCM-41 synthesized at relatively low temperature (100 degreesC) shows the Q(4)/Q(3) + Q(2) ratio at 1.1. Such unique structural feature might be responsible for the observed highly hydrothermal stability of the mesoporous silica materials (JLU-30).

A novel method to synthesize amorphous silica-alumina materials with mesoporous distribution without using templates and pore-regulating agents

In this study, a novel sol-gel method is used to synthesize amorphous silica-alumina materials with a narrow mesoporous distribution and various Si/Al molar ratios without using any templates and pore-regulating agents. During the preparation procedure, only inexpensive inorganic salts were used as raw materials, instead of expensive and harmful alkoxides. The precursor sol was dried at room temperature in a vacuum box kept at 60 mmHg until it began to form the gel. The results of a nitrogen sorption experiment indicate that the synthesized materials with different Si/Al molar ratios have similar mesoporous distributions (within 2-12 nm). Moreover, it was found that the material's pore size distribution remains at a similar value during the heat treatment from room temperature to 550 degreesC. On the basis of the nitrogen sorption, TEM, and AFM characterization results, a formation mechanism of mesopores which accounts for the experimental data is also suggested. This suggested mechanism involves rearrangement of the primary particles during the drying process to form the precursors of the similarly sized mesopores. The synthesized materials were characterized by XRD, thermal analysis (TG/DTA), Al-27 and Si-29 MAS NMR spectroscopy, SEM, TEM, and AFM. The results of Al-27 and 29Si MAS NMR indicate that the distribution of silicon and aluminum in the synthesized materials is more uniform and homogeneous than that in the mixed oxides prepared via the traditional sol-gel method even at high alumina contents. The type and density of the acid sites were studied using pyridine adsorption-desorption FTIR spectroscopy. It was shown that the acidity of the synthesized materials is higher than that of the silica-alumina materials prepared by conventional methods.

Hydrothermal stability and catalytic activity of aluminum-containing mesoporous ethane-silicas

Aluminum was incorporated into the mesoporous framework of ethane-silica by one-pot condensation of Al(OiPr)(3) with 1,2-bis(trimethoxysilyl)ethane using octadecyltrimethylammonium chloride as surfactant. Powder X-ray diffraction patterns, nitrogen sorption analysis, and TEM results reveal the formation of an ordered mesoporous material with uniform porosity. Al-27 MAS NMR confirms the incorporation of aluminum in the framework. The synthesized materials exhibit extremely high hydrothermal stability in boiling water (no obvious change of mesostructure and textural properties was observed even after refluxing in water for 100 h), which could be mainly contributed to the ethane-bridged mesoporous framework. The aluminum-containing mesoporous ethane-silicas are efficient catalysts for the alkylation of 2,4-di-tert-butylphenol by cinnamyl alcohol to yield a flavan.

Synthesis of carbon nanotube bundles with mesoporous structure by a self-assembly solvothermal route

A kind of carbon nanotube bundle has been synthesized by a simple one-step solvothermal reaction between Na and hexachlorobenzene (HCB) using NiCl2 as catalyst precursor. Before the reaction, NiCl2 was initially dispersed ultrasonically in cyclohexane then prereduced by Na at 230degreesC to produce small Ni particles in reduced state. The tubes thus-produced have a uniform outer diameter of about 20 nm, an inner diameter of 4 nm, and are highly ordered assembled as bundles which have a 2D hexagonal arrangement as proven by SAXS and TEM experiments.

Near-infrared emission from novel tris(8-hydroxyquinolinate)lanthanide(III) complexes-functionalized mesoporous SBA-15

A novel mesoporous material covalently bonded with 8-hydroxyquinoline (HQ) was synthesized (designated as Q-SBA-15). The 5-formyl-8-hydroxyquinoline grafted to.(3-aminopropyl)triethoxysilane, that is, alkoxysilane modified 8-hydroxyquinoline (Q-Si), was used as one of the precursors for the preparation of the Q-SBA-15 material. On the basis of the other function of the Q-Si of coordinating to lanthanide (Ln) ions, for the first time, the LnQ(3) complexes (Ln = Er, Nd, Yb) have been covalently bonded to the SBA-15 materials.