Closely Packed Zeolite Nanocrystals Obtained via Transformation of Porous Amorphous Silica

Abstract

Amorphous silica grains were subjected to a hydrothermal treatment to be transformed into closely packed ZSM-5 zeolite nanocrystalline bodies. Three synthesis approaches have been developed: (I) direct hydrothermal treatment of the amorphous silica grains in a ZSM-5 precursor solution; (II) impregnation of charge-reversed amorphous silica grains with 2-10 nm preorganized units followed by a hydrothermal treatment in a silica-free precursor synthesis solution; and (III) electrostatic adsorption of 50-nm sized ZSM-5 seeds on the amorphous silica grains followed by a hydrothermal treatment with a ZSM-5 precursor solution. The synthesized solids were characterized by X-ray diffraction, Raman spectroscopy, TG analysis, N 2 adsorption measurements, and scanning electron microscopy. The resulted zeolitic bodies are built of uniform closely packed nanocrystals and retain the size and morphological features of the initial amorphous silica grains. The crystallinity, the average size of crystallites, and the mechanical properties of the nanozeolite bodies depend strongly on the synthesis procedure. It was found that procedure II provides mechanically stable bodies built of closely packed nanocrystallites with a size of about 40 nm, which are very promising for the production of self-bonded nanozeolite structures.

The Fabrication of Ga2O3/ZSM-5 Hollow Fibers for Efficient Catalytic Conversion of n-Butane into Light Olefins and Aromatics

“…(A) (B) [12,36] except that the addition of NaOH and the synthesis was carried out at 100˝C for 72 h. When the synthesis was completed, the nanocrystals products were washed, dried, and calcined at 550˝C for 6 h in muffle furnace followed by ion-exchanged, dried, and calcined process. The zeolite prepared according to the above methods is denoted Nano-ZSM-5 (with an actual Si/Al of 55 determined by XRF).…”

Modern Spectroscopic Methods Applied to Nanoscale Porous Materials

“…Raman spectroscopy was applied to probe the degree of structural disorder in micron-sized self-assemblies of closely packed zeolitic nanocrystallites (BEA and MFI), prepared via transformation of porous amorphous silica under thermal treatment. 22,26 Insights into structural defects are gained from the spectra collected from calcined samples. The Raman scattering near 960 cm À1 is indicative for point defects in the silicon-oxygen framework (violated Si-O-Si linkages), while the percentage of non-crystalline domains in the samples prepared by different methods can be quantified by fitting the shape of the multi-component band in the range 250-650 cm À1 , generated by SiO 4 -ring modes.…”

“…Thus FTIR and Raman spectroscopic methods are very efficient for studying kinetic processes and precursor clusters as well as to identify small-sized crystalline particles in the final product. 10,13,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In addition, FTIR and Raman spectroscopy are very sensitive to atomic bonding and thus gives the opportunity to study active sides and interactions between embedded functional molecules and framework atoms in porous materials. 5,12,[33][34][35][36][37][38][39][40][41][42] Raman spectroscopy compares favourably to FTIR spectroscopy because of the better signal-to-noise ratio in the low-energy spectral range and the better spatial resolution when a microscope is used.…”

New mesoporous silica/carbon composites byin situtransformation of silica template in carbon/silica nanocomposite

“…However, it always requires the selective removal of silica template in the carbon/silica nanocomposite using harmful etchants such as HF and NaOH, and therefore it can cause serious potential problems such as waste of valuable chemicals and treatment of toxic chemical wastes, increasing the fabrication cost and posing environmental concerns. The synthesis of zeolite crystals by recrystallisation transformation of amorphous silica solution has been reported [17][18][19][20][21]. Recrystallisation is induced by introducing templating molecules such as tetrapropylammonium (TPA) into silica solution for zeolite crystallisation according to Oswald's rule [22].…”