A. Galarneau

New trends in the design of supported catalysts on mesoporous silicas and their applications in fine chemicals

Different strategies leading to the preparation of acid and base catalysts derived from ordered mesoporous silicas are reviewed. These include aluminum incorporation into the silicate network, entrapping of heteropolyacids, deposition of oxide precursors and direct or post-synthesis of anchoring of organic moieties. Their use in a variety of reactions related to fine chemicals synthesis is critically discussed.

Molecular Simulation of Nitrogen Adsorption in Nanoporous Silica

This article reports on a molecular simulation study of nitrogen adsorption and condensation at 77 K in atomistic silica cylindrical nanopores (MCM-41). Two models are considered for the nitrogen molecule and its interaction with the silica substrate. In the pea model, the nitrogen molecule is described as a single Lennard-Jones sphere and only Lennard-Jones interactions between the nitrogen molecule and the oxygens atoms of the silica substrate are taken into account. In the bean model (TraPPE force field), the nitrogen molecule is composed of two Lennard-Jones sites and a linear array of three charges on the atomic positions and at the center of the nitrogen-nitrogen bond. In the bean model, the interactions between the sites on the nitrogen molecule and the Si, O, and H atoms of the substrate are the sum of the Coulombic and dispersion interactions with a repulsive short-range contribution. The data obtained with the pea and bean models in silica nanopores conform to the typical behavior observed in the experiments for adsorption/condensation in cylindrical MCM-41 nanopores; the adsorbed amount increases continuously in the multilayer adsorption regime until an irreversible jump occurs because of capillary condensation and evaporation of the fluid within the pore. Our results suggest that the pea model can be used for characterization purposes where one is interested in capturing the global experimental behavior upon adsorption and desorption in silica nanopores. However, the bean model is more suitable to investigating the details of the interaction with the surface because this model, which accounts for the partial charges located on the nitrogen atoms of the molecule (quadrupole), allows a description of the specific interactions between this adsorbate and silica surfaces (silanol groups and siloxane bridges) or grafted silica surfaces. In particular, the bean model provides a more realistic picture of nitrogen adsorption in the vicinity of silica surfaces or confined in silica nanopores, where the isosteric heat of adsorption curves show that the nitrogen molecule in this model is sensitive to the surface heterogeneity.

29-O-02 Towards total hydrophobisation of MCM-41 type silica surface

Publisher Summary This chapter presents the refinement of the procedure for MCM-41 surface fictionalization with various octylsilanes to obtain a maximum surface coverage. Two different types of surface modification using different grafting agents are performed on micellar templated silica (MTS) samples. MTS samples possessing three different pore sizes are functionalized by the hydrolysis and polymerization of pre-adsorbed monolayer of octylsilanes on MTS surface or by chlorine substitution from chlorooctylsilane with nucleophilic assistance. The effect of various experimental parameters on the hydrophobicity and the grafted chain loading is also analyzed.

Removal of perfluorooctanoic acid from water by adsorption on high surface area mesoporous materials

Abstract Removal of perfluorinated alkylated substances (PFAS) such as perfluorooctanoic acid (PFOA) from aqueous solution is an actual topic in light of their widespread diffusion and their persistence in the environment. The process of adsorption has been identified as an effective technique to eliminate PFAS in water, however the process efficiency strongly depends on the adsorbents employed (silica, alumina, activated carbon, layer doubled hydroxides). In this work three nanostructured mesoporous silica materials of similar pore diameter (~4xa0nm) featuring high surface area (~900xa0m2/g) and high pore volume (0.7–1.0xa0mL/g) were evaluated in PFOA removal: calcined MCM-41 (MCM-41c), calcined hexagonal mesoporous silica (HMSc) and HMSe obtained after ethanol extraction of the amine templates from HMS. Sorption kinetics and isotherms were performed at PFOA concentrations from 10xa0µg/Lxa0to 10xa0mg/L. It appeared that HMSe showed much faster and higher adsorption capacity for PFOA than the other tested adsorbents (MCM-41c and HMSc) whatever the pH of the solution (5xa0<xa0pHxa0<xa09). Thermogravimetric analysis of HMSe evidenced that the ethanol extraction of the templating amines was not complete (70xa0%) and HMSe possessed some remaining hexadecylamine (HDA) (0.08xa0mol amine per mol SiO2) on the surface conferring some hydrophobic properties to the adsorbent and also some probable complex formation between anionic PFOA− and protonated HDA. Indeed, the incomplete amine extraction is surely due to the presence of protonated HDA in strong electrostatic interactions with SiO− avoiding their removal by simple ethanol extraction as for H-bonding amine with Si–OH groups. Considering both adsorption isotherms and adsorption kinetics, PFOA could be efficiently removed from contaminated water in a wide range of concentration by an environmental friendly adsorbent as HMSe.

06-P-27 - Swelled micelle-templated silicas (MTS): structure control and hydrophobic properties

Publisher Summary This chapter discusses swelled micelle-templated silicas (MTS). The synthesis of swelled-MTS with cylindrical mesopores is highly dependent on the nature of the swelling agent: aromatics allow preserving the cylindrical geometry of pores and aliphatics change pore geometry to a system of interconnected spheres. This is due to the different sites of solubilization of the organics in cetyltrimethylammonium bromide (CTAB) micelles. For polarizable molecules, there are two sites of solubilization—namely, near the micellar interface (interaction with ammonium head group) and in the micellar core. Aliphatic molecules are directly dissolved in the center of the micelles. Purely silliceous and aluminosilicates MTS with regular cylindrical pores up to 150 A are obtained.

Amine-free lecithin templating of sponge mesoporous silicas

The synthesis of lecithin-templated sponge mesoporous silicas (SMS) in the absence of fatty amines improves their biocompatibility and sheds some light on their mechanism of formation.

HMS materials with high Al loading: a joint FT-IR and microcalorimetric study of their acidic/basic properties

Abstract HMS materials with Si/Al ratio = 2.5 have been synthesised and characterized. 27 A1 NMR spectra showed minimal occurrence of octahedral phase after template removal. FT-IR and microcalorimetric results showed that, though having the same chemical composition of Y zeolites, such materials exhibit drastically different acidic/basic properties.

Revelation on the complex nature of mesoporous hierarchical FAU-Y zeolites

The texture of mesoporous FAU-Y (FAUmes) prepared by surfactant-templating in basic media is a subject of debate. It is proposed that mesoporous FAU-Y consists of: (1) ordered mesoporous zeolite networks formed by a surfactant-assisted zeolite rearrangement process involving local dissolution and reconstruction of the crystalline framework, and (2) ordered mesoporous amorphous phases as Al-MCM-41, which coexist with zeolite nanodomains obtained by a dissolution-reassembly process. By the present systematic study, performed with FAU-Y (Si/Al = 15) in the presence of octadecyltrimethylammonium bromide and 0 < NaOH/Si ratio < 0.25 at 115 °C for 20 h, we demonstrate that mesoporous FAU zeolites consist, in fact, of a complex family of materials with textural features strongly impacted by the experimental conditions. Two main families have been disclosed: (1) for 0.0625 < NaOH/Si < 0.10, FAUmes are ordered mesoporous materials with zeolite walls, which coexist with zeolite nanodomains (100-200 nm) and (2) for 0.125 < NaOH/Si < 0.25, FAUmes are ordered mesoporous materials with amorphous walls as Al-MCM-41, which coexist with zeolite nanodomains (5-100 nm). The zeolite nanodomains decrease in size with the increase of NaOH/Si ratio. Increasing NaOH/Si ratio leads to an increase of mesopore volume, while the total surface area remains constant, and to a decrease of strong acidity in line with the decrease of micropore volume. The ordered mesoporous materials with zeolite walls feature the highest acidity strength. The ordered mesoporous materials with amorphous walls present additional large pores (50-200 nm), which increase in size and amount with the increase of NaOH/Si ratio. This alkaline treatment of FAU-Y represents a way to obtain ordered mesoporous materials with zeolite walls with high mesopore volume for NaOH/Si = 0.10 and a new way to synthesize mesoporous Al-MCM-41 materials containing extralarge pores (50-200 nm) ideal for optimal diffusion (NaOH/Si = 0.25).

29-O-04-A controlled dispersion of Al3+ onto a silica mesoporous material A comparative study with Al3+ incorporation

Publisher Summary This chapter describes a controlled dispersion of Al 3+ onto a silica mesoporous material. A pure silica MCM-48 is activated by a controlled dispersion of Al onto the substrate surface performed by the anchoring of the Al(acac) 3 complex onto the surface silanols. A calcinations step removes the organic ligands. The characteristics of the final structure are evaluated by comparison with Al incorporated MCM-48. The type and concentration of Lewis/BrOnsted acid sites are also investigated by the adsorption of ammonia (NH 3 ) and acetonitrile-d3 (CD 3 CN).