A High-Yield Reproducible Synthesis of MCM-48 Starting from Fumed Silica

Abstract

A new synthesis pathway for MCM-48 is developed using fumed silica as the silicate source and a Gemini surfactant (GEM 16-12-16) as the surface directing agent. Different synthesis parameters have been optimized in order to obtain a highly ordered mesostructure. The determining factor in the stabilization of the final structure is proven to be a double post-synthesis hydrothermal treatment. This treatment, performed successively in a minimum of pure water at 403 K, reduces the pH of the gel, allowing a better condensation of the silicate structure. Other parameters of importance are the OH-/Si ratio, the gelation time, and the synthesis temperature, influencing the solubility of the fumed silica, the condensation and the structuring of the silicate framework, and the pore diameter, respectively. The synthesis temperature has also a positive effect on the particle dimension, producing uniform grains of 4−5 μm. The optimized parameters (3-day gelation time followed by two consecutive post-synthesis hydrothermal treatments) give a highly reproducible synthesis, with a high silica yield (70−75%). The synthesized samples have been characterized using XRD, N2 sorption isotherms, SEM, and infrared (DRIFT) measurements.

Hydroconversion of n-hexadecane over bifunctional microporous and mesoporous model catalysts. Influence of pore architecture on selectivity

“…Procedures have been described in detail in previous papers [6,17,18]. Surface acidity was probed by ammonia TPD and IR spectroscopy of adsorbed perdeuterated acetonitrile (99.8% D atom, Aldrich).…”

“…6.223 g of CTAB were then added. After complete dissolution 6 g of silica were introduced and the mixture was stirred for 2 h. The reactor was then sealed and placed in an oven without stirring for 7-10 h. In order to prepare MCM-48 materials with improved thermal and mechanical stability [17,18] the solid precipitate was filtered, washed, and subjected to two successive post-synthesis treatments in de-ionized water (7.5 g H 2 O per gram of solid) at 403 K for 2 h. The solid was dried in an oven at 393 K and then calcined in flowing air at 823 K for 8 h.…”

New Insights in the Formation of Combined Zeolitic/Mesoporous Materials by using a One‐Pot Templating Synthesis

“…[9] The FTIR band at 1050 cm -1 (Figure 4a and enlarged in Figure 4b) is slightly shifted to higher wavenumbers when the temperature is higher than 100°C, meaning that the Si-O-Si bond strength increases due to shortening of the silicate bonds and this is due to a better condensation at elevated temperature. [12] The grey arrow is the peak maximum of meso-TSM-2d-100°C, whereas the black arrow indicates that of meso-TSM-2d-125°C and meso-TSM-2d-150°C. The differences observed in the FTIR spectra are small, but significant.…”

Synthesis and aqueous solution properties of homologous gemini surfactants with different head groups

“…So they were widely used as effective emulsifiers, bactericidal agents, dispersants, anti-foaming agents, detergents, etc. Recently these compounds were also applicable in the solubilization of dyes and pigments in the textile industry [10], gene therapy [11], the synthesis of highly mesoporous materials [12], etc. Nowadays, they are one of the most interesting objects of surface science.…”