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The catalytic activity of supported silver nanoparticles on mesoporous silica was studied, for the selective reduction of azines into benzyl hydrazones using sodium borohydride as mild reducing agent. Different sizes of silver nanoparticles supported on mesoporous silica (Ag/HMS) were successfully prepared by two methods, i.e. wet impregnation followed by reduction with hydrogen at 350oC and in situ deposition/reduction with a mixture of amines (ethanolamine and ethylenediamine). The Ag/HMS (amines) catalyst was found to promote the selective 1,2-reduction of aryl-substituted azines, compared to the corresponding 1,4-reduction that occurs in general reduction processes. This catalytic transfer hydrogenation process found to be clear, fast and quantitative (>99% yields and selectivity) towards benzyl hydrazones synthesis under mild conditions. Of great importance is that under the present catalytic conditions reducible functional groups remain intact. Formal kinetics, support the in situ formation of silver-hydride species being responsible for the reduction process. The presence of protic polar methanol enhanced the catalytic activity of Ag/HMS. Based on the recycling studies the catalytic system Ag/HMS-NaBH4 was found to catalyze the selective reduction of azines nine times without significant loss of its activity. Finally, one-pot reaction between the in situ produced benzyl hydrazones and a series of nitrostyrenes readily provided the regioselective synthesis of 1,3,5,-subtituted pyrazoles, highlighting a useful synthetic application of the catalytic protocol.

Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst.

Isomerization of glucose to fructose is an important reaction with numerous applications in terms of biomass valorization. The reaction is catalyzed enzymatically but may also proceed under alkaline conditions, in which case it is accompanied by low selectivity and formation of byproducts. Solid Lewis acid and basic catalytic materials are being studied as alternative catalysts. In this work, the isomerization of glucose to fructose in aqueous media over homogeneous and heterogeneous catalysts has been investigated. The effect of polar aprotic solvents and their mixtures with water on glucose conversion and fructose selectivity was also studied. Sodium aluminate (NaAlO2) has been proven to be very effective, resulting in high fructose yield (52.1 %) and high selectivity (84.8 %). Among the various solid catalysts tested, MgO afforded glucose conversion of 44 %, with 75.8 % and 33.4 % fructose selectivity and yield, respectively, when the isomerization reaction was conducted in neat H2O.

The application of heterogeneous catalysis in biomass pyrolysis is considered as one of the most promising methods to improve bio‐oil quality by minimizing its undesirable properties (high viscosity, corrosivity, instability, etc.) and producing renewable fuels and high‐value chemicals. Catalytic fast pyrolysis (CFP) of biomass refers both to the “in situ” and “ex situ or two‐stage” upgrading. A plethora of catalytic materials have been investigated in the literature for both approaches, including conventional microporous zeolites, ordered mesoporous aluminosilicates, promoted or not with several transition metals, as well as various metal (nano)oxide catalysts with Lewis acidity. Recently, hybrid micro/mesoporous and basic materials have been also suggested exhibiting most promising results due to combined micro/mesoporosity and adequate balance of acid and basic sites. Optimum catalysts are required to retain deoxygenation, enhance yields of aromatics, and other valuable compounds (such as phenolics), while limiting coke formation. Coke formation is one of the reasons of catalyst deactivation; a very challenging issue during biomass CFP, especially using zeolites. The deactivation process is affected by many factors, including the composition of the feedstock (inorganic minerals present in the feedstock may also deposit on the catalyst), reaction conditions, and the nature/properties of the catalysts used in CFP. Precoking on the surface of zeolites or MgO deposition are among the proposed effective ways to suppress coke formation and thus, catalyst deactivation. This article is categorized under: Bioenergy > Science and Materials Energy Research & Innovation > Science and Materials Energy and Transport > Science and Materials

The natural resistance to enzymatic deconstruction exhibited by lignocellulosic materials has designated pretreatment as a key step in the biological conversion of biomass to ethanol. Hydrothermal pretreatment in pure water represents a challenging approach because it is a method with low operational costs and does not involve the use of organic solvents, difficult to handle chemicals, and "external" liquid or solid catalysts. In the present work, a systematic study has been performed to optimize the hydrothermal treatment of lignocellulosic biomass (beech wood) with the aim of maximizing the enzymatic digestibility of cellulose in the treated solids and obtaining a liquid side product that could also be utilized for the production of ethanol or valuable chemicals. Hydrothermal treatment experiments were conducted in a batch-mode, high-pressure reactor under autogeneous pressure at varying temperature (130-220 °C) and time (15-180 min) regimes, and at a liquid-to-solid ratio (LSR) of 15. The intensification of the process was expressed by the severity factor, log R(o). The major changes induced in the solid biomass were the dissolution/removal of hemicellulose to the process liquid and the partial removal and relocation of lignin on the external surface of biomass particles in the form of recondensed droplets. The above structural changes led to a 2.5-fold increase in surface area and total pore volume of the pretreated biomass solids. The enzymatic hydrolysis of cellulose to glucose increased from less than 7 wt% for the parent biomass to as high as 70 wt% for the treated solids. Maximum xylan recovery (60 wt%) in the hydrothermal process liquid was observed at about 80 wt% hemicellulose removal; this was accomplished by moderate treatment severities (log R(o)=3.8-4.1). At higher severities (log R(o)=4.7), xylose degradation products, mainly furfural and formic acid, were the predominant chemicals formed.

Application of heterogeneous catalysis in biomass pyrolysis seems to be one of the most promising methods to improve bio-oil quality by minimizing its undesirable properties (high viscosity, corrosivity, instability, etc.) and producing renewable crude (bio-crude). This bio-crude could finally lead to transportation fuels using existing refinery processes (such as hydrotreating). A plethora of catalytic materials have been investigated in the literature as catalysts for the biomass catalytic pyrolysis process. Among them, microporous (zeolitic) or mesoporous (Al-MCM-41) acid materials have been tested, either promoted or not with several transition metals. Lately, basic materials are also suggested. For this process, a circulating fluid bed reactor seems to be the most effective technology, since it offers continuous catalyst regeneration. The research till today shows that catalysts based on ZSM- are the most promising. With these catalysts, bio-oil yield up to about 30 wt% (on dry biomass) with about 21 wt% oxygen can be produced. However, tailoring of catalyst properties such as acidity/basicity and porosity characteristics is still needed to develop an optimized catalyst.

BACKGROUND: Water-soluble reactive azo dyes are the most problematic dye house effluents, as they tend to pass through conventional treatment systems unaffected. The release of these compounds into the environment is undesirable and their removal becomes environmentally important. In this work, synthesis, characterization and sorption properties of hydotalcite-like compounds (Mg/Al and Mg/Fe), calcined and uncalcined, were investigated for the removal of the reactive azo dye Remazol Red 3BS. RESULTS: The calcined compounds present higher surface area than the uncalcined. The optimum pH for sorption was found to be 6. Thermodynamic analysis reveals that the sorption is spontaneous and endothermic. Equilibrium data were fitted by a Langmuir model, and kinetic data by a second-order model. The calcined Mg/Al compound showed the highest sorption capacity, at 0.125 mmol g−1. Regeneration of dye loaded derivative is achieved using the surfactant SDS. CONCLUSIONS: The prepared hydotalcite-like compounds and especially calcined Mg-Al exhibited significant adsorption capacity, kinetics, and regenerative ability. Its potential applicability as sorbent should be tested in a large-scale implementation. Copyright © 2011 Society of Chemical Industry

Low-density polyethylene (LDPE)/silicate nanocomposites were prepared by the melt compounding and solution blend methods using unmodified LDPE polymer and layered silicates with different aspect ratio. X-ray diffraction (XRD) analysis performed on composites obtained by dispersing the organosilicates in molten LDPE evidenced an exfoliated or partially exfoliated structure for the low aspect ratio silicate (laponite) in contrast to the high aspect ratio silicate (montmorillonite), which led to the formation of intercalated nanocomposites. With regard to the preparation method, the melt compounding method was more effective in forming exfoliated/highly intercalated LDPE nanocomposites compared with the solution blend method (using CCl4 as a solvent). A gradual increase in crystallization temperatures (Tc) with increasing laponite content for LDPE-organolaponite nanocomposites was revealed by differential scanning calorimetry (DSC) measurements. Thermogravimetric analysis and tensile measurements results indicated that thermal stability and elastic modulus increment were more prevalent for nanocomposites prepared using organomontmorillonite as filler. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The use of homoionic organic clays and mixed-ion organic/inorganic clays modified by di- or triamines (Jeffamines), which are being used as epoxy resin curing agents, in the synthesis of polymer nanocomposites has been studied in this work. Our aim is to enhance polymer crosslinking and interfacial adhesion in the nanocomposite structure by utilizing the functionality of the di/triamines on the surface of clay nanolayers and by reducing the organic modifier via formation of homostructured mixed-ion organic/inorganic clays. The results show that the use of homoionic organic clays exchanged with relatively short chain di- or triamines and mixed-ion organic/inorganic clays partially exchanged (ca. 35%) with long chain diamines resulted in intercalated structures with enhanced thermo-mechanical properties (Young's Modulus, Storage Modulus). On the other hand, homoionic organic clays exchanged with long chain diamines and triamines resulted in exfoliated nanocomposites but with compromised mechanical properties due to the plasticizing effect of the long chain amine modifiers.

This paper discusses settling rates, yield stresses, and shear-stress/shear-rate dependences which were determined as functions of solids concentration for suspensions in water of coal particles of narrow size fractions. Particles and suspensions are characterized by coal analyses, determination of heating value, solid heat capacity and thermal conductivity, particle size analyses, and determination of densities and maximum packing concentrations for each particle size range. Analysis of the settling data establishes that the usually strong retardation of (hindered) settling due to concentration is compounded by particle shape effects. Shear-stress/shear-rate data for concentrated suspensions of the three larger and relatively narrower sized particles over the broad range of shear rates from about 1 to 10{sup 4} s {sup {minus}1} suggest the behavior to be essentially Newtonian, albeit with a marked particle concentration augmentation. Suspensions of the smallest coal particles of broader size distribution were strongly non-Newtonian, possessing a yield stress at low shear, essentially power-law shear-thinning behavior over the intermediate range and approaching high-shear Newtonian limiting behavior above about 10{sup 3} s{sup {minus}1}.