Dry gel conversion of organosilane templated mesoporous silica: from amorphous to crystalline catalysts for benzene oxidation

Mesoporous silica grown using [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride as the mesoporogen in the presence of Fe and Al is X-ray amorphous, but contains very small domains with features of MFI zeolite as evidenced by IR and Raman spectroscopy. When applied as a catalyst, this amorphous sample shows good performance in the selective oxidation of benzene using nitrous oxide. Addition of tetrapropylammonium as structure directing agent to the as-synthesized mesoporous silica and subsequent dry gel conversion results in the formation of hierarchical Fe/ZSM-5 zeolite. During dry gel conversion the wormhole mesostructure of the initial material is completely lost. A dominant feature of the texture after crystallization is the high interconnectivity of micropores and mesopores. Substantial redistribution of low-dispersed Fe takes place during dry gel conversion towards highly dispersed isolated Fe species outside the zeolite framework. The catalytic performance in the oxidation of benzene to phenol of these highly mesoporous zeolites is appreciably higher than that of the parent material.

Adsorption Study using Optimised 3D Organised Mesoporous Silica Coated with Fe and Al Oxides for Specific As(III) and As(V) Removal from Contaminated Synthetic Groundwater

This work presents the possibility of optimising 3D Organised Mesoporous Silica (OMS) coated with both iron and aluminium oxides for the optimal removal of As(III) and As(V) from synthetic contaminated water. The materials developed were fully characterised and were tested for removing arsenic in batch experiments. The effect of total Al to Fe oxides coating on the selective removal of As(III) and As(V) was studied. It was shown that 8% metal coating was the optimal configuration for the coated OMS materials in removing arsenic. The effect of arsenic initial concentration and pH, kinetics and diffusion mechanisms was studied, modelled and discussed. It was shown that the advantage of an organised material over an un-structured sorbent was very limited in terms of kinetic and diffusion under the experimental conditions. It was shown that physisorption was the main adsorption process involved in As removal by the coated OMS. Maximum adsorption capacity of 55 mg As(V).g-1 was noticed at pH 5 for material coated with 8% Al oxides while 35 mg As(V).g-1 was removed at pH 4 for equivalent material coated with Fe oxides.

An effective three-dimensional ordered mesoporous ZnCo2O4 as electrocatalyst for Li-O2 batteries

Three-dimensional ordered mesoporous (3DOM) ZnCo₂O₄ materials have been synthesized via a hard template and used as bifunctional electrocatalysts for rechargeable Li-O₂ batteries. The as-prepared ZnCo₂O₄ nanoparticles possess a high specific surface area of 127.2 m² g^-1 and a spinel crystalline structure. The Li-O₂ battery utilizing 3DOM ZnCo₂O₄ shows a higher specific capacity of 6024 mAh g^-1 than that with pure Ketjen black (KB). Moreover, the ZnCo₂O₄-based electrode enables much enhanced cyclability with a smaller discharge-recharge voltage gap than that of the carbon-only cathode. Such excellent catalytic performance of ZnCo₂O₄ could be associated with its larger surface area and 3D ordered mesoporous structure

An effective three-dimensional ordered mesoporous CuCo2O4 as electrocatalyst for Li-O2 batteries

Three-dimensional ordered mesoporous (3DOM) CuCo₂O₄ materials have been synthesized via a hard template and used as bifunctional electrocatalysts for rechargeable Li-O₂ batteries. The characterization of the catalyst by X-ray diffractometry and transmission electron microscopy confirms the formation of a single-phase, 3-dimensional, ordered mesoporous CuCo₂O₄ structure. The as-prepared CuCo₂O₄ nanoparticles possess a high specific surface area of 97.1 m² g^{- 1} and a spinel crystalline structure. Cyclic voltammetry demonstrates that mesoporous CuCo₂O₄ catalyst enhances the kinetics for either oxygen reduction reaction (ORR) or oxygen evolution reaction (OER). The Li-O₂ battery utilizing 3DOM CuCo₂O₄ shows a higher specific capacity of 7456 mAh g^{- 1} than that with pure Ketjen black (KB). Moreover, the CuCo₂O₄-based electrode enables much enhanced cyclability with a 610 mV smaller discharge-recharge voltage gap than that of the carbon-only cathode at a current rate of 100 mA g^{- 1}. Such excellent catalytic performance of CuCo₂O₄ could be associated with its larger surface area and 3D ordered mesoporous structure. The excellent electrochemical performances coupled with its facile and cost-effective way will render the 3D mesoporous CuCo₂O₄ nanostructures as attractive electrode materials for promising application in Li-O₂ batteries.

Determination of toluene hydrogenation kinetics with neutron diffraction

Total neutron scattering has been used to follow the hydrogenation of toluene-d₈ to methylcyclohexane-d₁₄ over 3 wt% platinum supported on highly ordered mesoporous silica (MCM-41) at 298 K and under 150 mbar D₂ pressure. The detailed kinetic information so revealed indicates that liquid reorganisation inside pores is the slowest step of the whole process. Additionally, the results were compared with the reaction performed under 250 mbar D₂ pressure as well as with toluene-h₈ hydrogenation using D₂ at 150 mbar.

Enhancement of the stability of microporous silica films in non-aqueous solvents at elevated temperature

The effect of Al incorporation and pH adjustment during hydrolysis of the silica precursor on the thermal and structural stability of ordered microporous silica films with a 2D structure is presented. The structural stability of the films was determined from a combination of LA XRD/TEM data with porosity data obtained from ethanol adsorption isotherms. Thermogravimetric analysis and MR data were used to determine the template removal and the thermal stability. Stability of aluminium incorporated silica films has further been examined in several organic solvents with different polarity. A solvent with a higher polarity interacts more strongly with the films; the long-order structure disappeared after exposure to polar solvents. After exposure to non-polar solvents, the pore size uniformity was retained after 48 h. The samples with an Al/Si ratio of 0.007 showed the smallest d-spacing shift after exposure to hexane. The stability was further tested in the hydrogenation of phenylacetylene performed in a batch reactor over 1 wt.% Pd/Si(Al)O-2/Si (Al/Si = 0.007) films at 30 degrees C and 10 bar H-2 with hexane as solvent. No deactivation was observed in two subsequent hydrogenation runs. (C) 2009 Elsevier Inc. All rights reserved.

Development of a heterogeneous catalyst for lignocellulosic biomass conversion:Glucose dehydration by metal chlorides in a silica-supported ionic liquid layer

An attempt is made to immobilize the homogeneous metal chloride/EMIMCl catalyst for glucose dehydration to 5-hydroxymethylfurfural. To this end, ionic liquid fragments were grafted to the surface of SBA-15 to generate a heterogenized mimick of the homogeneous reaction medium. Despite a decrease in the surface area, the ordered mesoporous structure of SBA-15 was largely retained. Metal chlorides dispersed in such ionic liquid film are able to convert glucose to HMF with much higher yields as is possible in the aqueous phase. The reactivity order CrCl > AlCl > CuCl > FeCl is similar to the order in the ionic liquid solvent, yet the selectivity are lower. The HMF yield of the most promising CrCl-Im-SBA-15 can be improved by using a HO:DMSO mixture as the reaction medium and a 2-butanol/MIBK extraction layer. Different attempts to decrease metal chloride leaching by using different solvents are described. © 2013 American Institute of Chemical Engineers Environ Prog.

Selectivity control in hydrogenation reactions by nanoconfinement of polymetallic nanoparticles in mesoporous thin films

A one-pot sol-gel synthesis method has been developed for the incorporation of metal nanoparticles into mesoporous oxide thin films deposited on various plane substrates by spin-coating and on the inner surface of fused silica capillaries by dip-coating. The size, the metal loading and the stoichiometry of the metal nanoparticles could be precisely controlled by following this methodology. In the first step, polymer stabilized Pt50Sn50 and Pt90Sn10 nanoparticles were obtained by a solvent-reduction method. Then, the nanoparticles were added to a metal oxide precursor sol, which was destabilized by solvent evaporation. After calcination, the obtained materials were tested in the hydrogenation of citral in both batch and continuous modes. The highest selectivity of 30% towards the unsaturated alcohols was obtained over supported Pt90Sn10 nanoparticles with a preferential formation of the cis-isomer (nerol) due to a unique confinement of the bimetallic nanoparticles in the mesoporous framework. The selectivity towards the unsaturated alcohols was further improved to 56% over the PtRu5Sn nanoparticles supported by impregnation onto mesoporous silica films. (C) 2009 Elsevier B.V. All rights reserved.

Determination of the Tolman length in the improved Derjaguin-Broekhoff-de Boer theory for capillary condensation of ethanol in mesoporous thin films by ellipsometric porosimetry

Ethanol adsorption-desorption isotherms on well-organized mesoporous silica and titania films with hexagonal pores structure were studied by ellipsometric porosimetry. The mesopore volume Was calculated from the change of the effective refractive index at the end points of the isotherm. An improved Derjaguin-Broekhoff-de Boer (IDBdB) model for cylindrical pores is proposed for the determination of the pore size. In this model, the disjoining pressure isotherms were obtained by measuring the thickness of the ethanol film on a non-porous film with the same chemical composition. This approach eliminates uncertainties related to the application of the statistical film thickness determined via t-plots in previous versions of the DBdB model. The deviation in the surface tension of ethanol in the mesopores from that of a flat interface was described by the Tolman parameter in the Gibbs-Tolman-Koening-Buff equation. A positive value of the Tolman parameter of 0.2 nm was found from the fitting of the desorption branch of the isotherms to the experimental data obtained by Low Angle X-ray Diffraction (LA-XRD) and Transmission Electron Microscopy (TEM) measurements in the range of pore diameters between 2.1 and 8.3 nm. (C) 2009 Elsevier Inc. All rights reserved.

Pharmacological Activity of Ibuprofen Release from Measoporous Silica

Novel drug delivery systems (DDS) to improve the pharmacokinetic profile of hydrophobic drugs following oral administration are an area of keen interest in drug research. An ideal DDS should not adversely affect drug activity, be capable of delivering a therapeutic dose of drug, and allow homogenous drug loading and drug release. Mesoporous silica has been proposed for this application, with ibuprofen employed as the model drug. It was hypothesised that mesoporous silica MCM-41 is capable of delivering a pharmacologically therapeutic dose of ibuprofen. Ibuprofen-loaded MCM-41 can be prepared reproducibly at a drug to carrier ratio of 30% (wt/wt). The release profile was seen to be 90% within 2 h. Initial assessment of COX-1 inhibitory activity suggests the absence of adverse effects attributable to drug-carrier interaction. The results of this study provide further evidence in support of the proposed use of mesoporous silica in drug delivery.