Lithium transition metal (Ti, Nb, V) oxide mesoporous thin films: contrasting results when attempting direct synthesis by evaporation-induced self assembly

in Microporous & Mesoporous Materials (2013), 172

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution ... [more ▼]

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H2O/TM ~10 (TM = Ti,Nb,V) and the common Pluronic structuring agent P123 (EO20-PO70-EO20). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350°C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions. [less ▲]

TiO2 mesoporous thin films studied by Atmospheric Ellipsometric Porosimetry: A case of contamination

in Microporous & Mesoporous Materials (2011), 147

Anatase mesoporous TiO2 thin films are frequently prepared by surfactant templating to control porosity development and Atmospheric Ellipsometric Porosimetry is a reliable and fast technique allowing the ... [more ▼]

Anatase mesoporous TiO2 thin films are frequently prepared by surfactant templating to control porosity development and Atmospheric Ellipsometric Porosimetry is a reliable and fast technique allowing the determination of the porosity of such films. After prolonged exposition to high-vacuum (6×10-6 mbar), the films porosity exhibits a degraded behavior during porosimetric measurements, indicating a vacuum-induced modification. The main effect resulting from such exposition to high-vacuum is a wet- tability modification of the films, resulting in an increase of the hydrophobic character of the TiO2 surface. This evolution induces non-correct results in porosimetric measurements due to the fact that the contact angle parameter needed to calculate the pore size distribution is highly different from the reference films. A surface contamination explains such modifications and a restoration of the films is obtained by using ultraviolet treatment. [less ▲]

Preparation and characterization of HMS supported 11-molybdo-vanado-phosphoric acid for selective oxidation of propylene

in Microporous & Mesoporous Materials (2010), 130(1-3), 103-114

The preparation of Keggin-type phosphovanadomolybdic acid H4PMo11VO40 (PMo11V) supported on a hexagonal mesoporous silicate (HMS) material was performed via three different methods: dry impregnation, wet ... [more ▼]

The preparation of Keggin-type phosphovanadomolybdic acid H4PMo11VO40 (PMo11V) supported on a hexagonal mesoporous silicate (HMS) material was performed via three different methods: dry impregnation, wet impregnation and mechanical mixing. The state of the heteropolyacid (HPA) on the siliceous surface and the integrity of the support were characterized by several physico-chemical techniques: elemental analysis, X-ray diffraction, transmission and diffuse reflectance (DR) FT-IR study of the framework vibrations, Raman and X-ray photoelectron spectroscopies, nitrogen physisorption, thermal analysis (TG-DTA) and scanning electron microscopy (SEM). The catalytic performance of supported materials was compared to that of the bulk H4PMo11VO40 in the selective oxidation of propylene by molecular oxygen in the temperature range of 200-400 °C. The physico-chemical characterization of the supported HPA showed mainly that the primary Keggin structure is intact and that a good dispersion of the heteropolyacid on the HMS surface is obtained when the impregnation methods are used. In the case of mechanical mixture, the dispersion of heteropolyacid clusters is not homogeneous. The surface area of HMS decreased when the HPA was added. The impregnation methods lead to mesopores with uniform size of approximatively 3.2 nm in diameter. The TG-DTA showed that the supported HPAs obtained by the impregnation methods have a higher thermal stability than that of bulk HPA. The catalytic results showed that H4PMo11VO40/HMS are more active than the bulk H4PMo11VO40 and lead to oxygenated compounds formation (acrolein, acetaldehyde and acetic acid), whereas the bulk HPA only leads to the formation of COx. © 2009 Elsevier Inc. All rights reserved. [less ▲]

Water desorption from resorcinol-formaldehyde hydrogels and adsorption in the resulting xerogels

in Microporous & Mesoporous Materials (2009), 117

Water desorption isotherms of resorcinol-formaldehyde (RF) hydrogels and subsequent water adsorption isotherms of the resulting xerogels are determined using the static gravimetric method, at various ... [more ▼]

Water desorption isotherms of resorcinol-formaldehyde (RF) hydrogels and subsequent water adsorption isotherms of the resulting xerogels are determined using the static gravimetric method, at various temperatures. Isotherms obtained from samples synthesized at various pH are compared. Two different mechanisms are involved in RF hydrogels water desorption. At large relative humidity the capillary tension resulting from water removal induces a macroscopic shrinkage of the gel, whereas at low humidity water is evaporated with no network deformation. These two mechanisms are analyzed using a plastic deformation model and the Guggenheim-Anderson-de Boer (GAB) model, respectively. Adsorption isotherms of RF xerogels are analyzed using the GAB model. [less ▲]

Tailor-made morphologies for Pd/SiO2 catalysts through sol-gel process with various silylated ligands

in Microporous & Mesoporous Materials (2008), 115

Chemistry of silica at different concentrations of non-ionic surfactant solutions: Effect of pH of the synthesis gel on the preparation of mesoporous silicas

in Microporous & Mesoporous Materials (2003), 63(1-3), 59-73

Ordered and disordered mesoporous silicas have been synthesized through an assembly of non-ionic decaoxyethylene cetyl ether [C 16(EO) 10] and a tetramethoxysilane silica source by variation of the pH ... [more ▼]

Ordered and disordered mesoporous silicas have been synthesized through an assembly of non-ionic decaoxyethylene cetyl ether [C 16(EO) 10] and a tetramethoxysilane silica source by variation of the pH value of the synthesis gel. The structure, texture and morphology of the mesoporous silicas, synthesized with concentrated and diluted surfactant solutions, have been discussed from the perspective of silica's chemistry upon a variation of pH values of the synthesis gel (micellar solution). With concentrated surfactant solutions (50 wt%), disordered compounds are obtained in a range of pH from 2.0 to 7.0 (micellar solution). As the pH increases, however, the pore size distributions (PSD) become broader and bimodality appears due to the micelle-templated silica (MTS) mesopores and openings arising from silica dissolution-reprecipitation processes. Also, the MTS pores expand due to a change in conformation of the surfactant hydrophilic head upon pH increase. On the other hand, diluted surfactant solutions (10 wt%) lead to ordered materials in a pH range from 2.0 to 7.0 (synthesis gel). The PSD remain very narrow but interparticular porosity appears and the morphologies undergo deep changes from toroids, gyroids and ropes to aggregates of very small particles with increasing pH. © 2003 Elsevier Inc. All rights reserved. [less ▲]