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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 350 °C 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 clean, fast and quantitative (>99% yields and selectivity) towards benzyl hydrazone 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, a 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

SUMMARY This paper discusses the use of H-infinity approximation for the online adaptation of PID controller parameters. For a frequency loop-shaping control objective, it is possible to adapt the PID parameters directly with linear model estimation algorithms. Standard least squares algorithms are common solutions for this problem, but their estimates exhibit a well-known strong dependence on the properties of the excitation. This drawback becomes more pronounced for systems where the modeling mismatch is large, as is frequently the case in PID control. In an alternative formulation of the estimation problem, we use a filter-bank to decompose the error signal to different components and minimize approximately the H-infinity norm of the sensitivity-weighted error operator. This approach results in a more consistent estimate of the optimal PID parameters, at the expense of higher excitation requirements. It also allows for the computation of a 'health indicator' to describe the confidence in the estimated parameters. The practical implication of this observation is that PIDs can be tuned more reliably, even in cases of large mismatch between the target and the feasible loop shapes. It also suggests a general theme where a min-max optimization of an operator error provides an advantage over signal error optimization. The key aspects of the algorithm are illustrated by numerical examples. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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 Ro. 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 Ro=3.8-4.1). At higher severities (log Ro=4.7), xylose degradation products, mainly furfural and formic acid, were the predominant chemicals formed. [ABSTRACT FROM AUTHOR]

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 MaterialsEnergy Research & Innovation > Science and MaterialsEnergy and Transport > Science and Materials Schematic description of the "in situ" and "ex situ" upgrading of pyrolysis vapours and catalyst deactivation due to either coke formation or deposition of biomass ash. [ABSTRACT FROM AUTHOR]