Valorisation of Biowastes for the Production of Green Materials Using Chemical Methods

With crude oil reserves dwindling, the hunt for a sustainable alternative feedstock for fuels and materials for our society continues to expand. The biorefinery concept has enjoyed both a surge in popularity and also vocal opposition to the idea of diverting food-grade land and crops for this purpose. The idea of using the inevitable wastes arising from biomass processing, particularly farming and food production, is, therefore, gaining more attention as the feedstock for the biorefinery. For the three main components of biomass—carbohydrates, lipids, and proteins—there are long-established processes for using some of these by-products. However, the recent advances in chemical technologies are expanding both the feedstocks available for processing and the products that be obtained. Herein, this review presents some of the more recent developments in processing these molecules for green materials, as well as case studies that bring these technologies and materials together into final products for applied usage

Process intensification by combination of activated carbon supported catalysts and alternative energy sources

Activated carbons are well known for their catalytic properties and for being used as a catalyst support in heterogeneous catalysis. Activated carbons possess most of the desired properties of a catalyst support; inertness towards unwanted reactions, stability under regeneration and reaction conditions, suitable mechanical properties, tunable surface area, porosity, and the possibility of being manufactured in different size and shape. On the other hand, the intensification of chemical transformations into valuable products through microwave and ultrasound activation has attracted particular attention in chemical industries in recent decades. Industrial chemical transformations are conventionally carried out by conductive heating by using an external heat source; a slow and inefficient way of transferring energy into the system. On the contrary, microwave irradiation and ultrasound are efficient ways of activating chemical systems. The short reaction time and expanded reaction range offered by microwave and ultrasound activation are appropriate in the development of new strategies for chemical transformations in industrial chemistry. In addition, the combination of activated carbon supported catalysts and microwave and ultrasound activation provides a peculiar activity and selectivity not reproducible under conventional thermal activation in a discontinuous batch reactorLos carbones activados son bien conocidos por sus propiedades catalíticas y por ser utilizados como soportes en catálisis heterogénea. Los carbones activados poseen muchas de las propiedades deseadas para un soporte catalítico; inactividad hacia reacciones no deseadas, estabilidad bajo condiciones de regeneración y de reacción, buenas propiedades mecánicas, área superficial modificable, porosidad, y posibilidad de ser fabricados en diferentes tamaños y formas . Por otra parte, la intensificación de transformaciones químicas en productos de alto valor añadido a través de la activación de microondas y los ultrasonidos ha despertado especial interés en las industrias químicas en las últimas décadas. Las transformaciones químicas industriales se llevan a cabo normalmente mediante calentamiento térmico convencional por conducción térmica utilizando una fuente de calor externa, una forma lenta e ineficiente de transferir energía al sistema. Por el contrario, la irradiación microondas y los ultrasonidos son una forma eficaz de activar los sistemas químicos. El corto tiempo de reacción y la gran reactividad mostrada por la activación microondas y la activación por ultrasonidos resultan apropiadas para el desarrollo de nuevas estrategias para las transformaciones orgánicas en la química industrial. Además, la combinación de catalizadores soportados sobre carbón activado y la activación por microondas y ultrasonidos, proporciona valores de actividad y selectividad característicos, no reproducibles bajo activación térmica convencional en un reactor discontinuo tipo batc

Monitoring the catalytic synthesis of glycerol carbonate by real-time attenuated total reflection FTIR spectroscopy

In situ Attenuated Total Reflectance FTIR spectroscopy was used to study the carbonylation of glycerol with urea. Cobalt oxide nanoparticles, Co3O4, hierarchically dispersed on zinc oxide microparticles, ZnO, were used as catalysts. The present work demonstrates that in situ real-time attenuated total reflection ATR-FTIR spectroscopy is a valuable tool for monitoring reaction progress and analyzing the reaction mechanism of the synthesis of glycerol carbonate. ATR-FTIR spectroscopy during the carbonylation reaction of glycerol with urea reveals differences in reactivity of various Co3O4/ZnO catalysts, and in particular demonstrates that the first (fast) step in the conversion of glycerol with urea is the formation of glycerol urethane, whereas the consecutive conversion to glycerol carbonate is relatively slow. In addition, possible interactions of the catalytically active sites with in particular the product glycerol carbonate were also evaluated. Interactions of the 2-hydroxyethyl chain of the product with the surface of the catalysts were identified, suggesting product inhibition might be of relevance to the reaction kinetics

Metal-free synthesis of quinolines catalyzed by carbon aerogels: Influence of the porous texture and surface chemistry

We report herein an experimental and theoretical study of the Friedländer reaction, from 2-amino-5-chlorobenzaldehyde and ethyl acetoacetate, catalyzed by free-metal nanocatalysts based on carbon aerogels, to afford quinoline 3a. The developed methodology implies the combined use of carbon aerogels with solvent-free technologies under MW irradiation yielding the corresponding quinoline with moderated yield (66%) in only 5 min of reaction time. Our results demonstrated that the reactivity of the samples upon MW irradiation is strongly dependent on the porosity and surface chemistry of the carbon aerogels, the most active catalytic species being the most acidic oxygenated functional groups, –COH groups originated by oxidant treatment, or even in situ by hydrolysis of –CO–O–CO–, over the carbon surface. The theoretical investigation of the reaction mechanism, by using computational methods, demonstrated that the synthesis of quinoline 3a in the absence or in the presence of carbon aerogels takes place by aldolization, subsequent heterocyclization and finally double dehydration. Relatively strong π-π stacking interactions between carbon support and reagents could be behind of the observed catalytic performance also extended for the oxygenated models. Furthermore, the concentration of –COH groups over the carbon surface is a key factor favoring each step of the reaction but acting as individual catalytic sites.This work has been supported by MICINN (CTM 2014-56668-R project). We are also grateful to the Centro de Supercomputación de Galicia (CESGA) for generous allocation of computing resources. MGO also thanks UNED for her PhD fellowship and VCC for her postdoctoral contractPeer Reviewe

Silica-based nanocatalysts in the C[sbnd]C and C-heteroatom bond forming cascade reactions for the synthesis of biologically active heterocyclic scaffolds

The design and development of hybrid materials with application in catalysis science is an interesting researching field, especially in the chemical industry for fine chemicals production. The properties of nanostructured catalysts can be changed by tuning the interaction between the support and the active phases. Silica nanoparticles are very convenient solid supports for the synthesis of organic-inorganic hybrid nanocatalysts, endowing them of the required features to optimize activity and selectivity, stability and recyclability. In this review, we analyze the latest developments and give a perspective concerning the recent applications of silica-based nanocatalysts for the synthesis of heterocyclic scaffolds, biologically active, via cascade reactions. Heterocyclic rings often are the structural cores responsible of the biological activities in natural products and synthetic compounds. These systems are frequently synthesized by multicomponent reactions (MCRs), through cascade reactions. Such versatile catalytic systems have been successfully applied in a great variety of organic transformations for the synthesis of complex molecules and would play a key role in establishing new and more efficient sustainable technologies.This work has been supported by MICINN (project CTM2014-56668-R). VCC thanks UNED for her postdoctoral contract.Peer Reviewe

Real-Time Raman Monitoring and Control of the Catalytic Acetalization of Glycerol with Acetone over Modified Mesoporous Cellular Foams

The acetalization of glycerol with acetone over modified mesoporous cellular foam materials has been widely investigated using in situ Raman spectroscopy during reaction. Mesoporous cellular foams (MCFs) modified by niobium or tantalum and (3-mercapto­propyl)­tri­methoxy­silane (MP) followed by H₂O₂ treatment were used as catalysts in the acetalization of glycerol with acetone. The influence of the type of catalyst, which determines the solid texture and number of Brønsted acid sites, and different reaction parameters, such as reaction time, reaction temperature, glycerol/acetone ratio, and catalyst amount on acetalization reaction, were investigated. The results obtained in the characterization of the catalysts show that the materials obtained differ in the number of Brønsted acidic sites. Raman spectroscopy provides noninvasive insight during acetalization of glycerol with acetone in the presence of acid heterogeneous catalysts. The progress of the acetalization reaction was monitored following the variation in intensity of characteristic Raman bands and using chemometric analyses. The results obtained by real-time Raman monitoring confirm the mechanism proposed for the reaction, which proceeds via the formation of the 3-(2-hydroxy­propan-2-yloxy)­propane-1,2-diol intermediate, whose presence is confirmed by Raman spectroscopy. Under optimal reaction conditions, the 5-membered ring ketal 2,2-di­methyl-1,3-di­oxolane-4-yl methanol (solketal) was obtained with the highest selectivity (99%). Raman monitoring enables real-time control of the reaction, thus enabling the optimization of reaction conditions for a more efficient reaction. Raman monitoring illustrates the reversibility of the reaction upon evaporation of acetone, even under reflux

Y zeolite-supported niobium pentoxide catalysts for the glycerol acetalization reaction

Supplementary data related to this article can be found at http://dx. doi.org/10.1016/j.micromeso.2018.06.010.Faujasite zeolite-supported niobium-based catalysts (with Nb2O5 amounts of 5 and 15wt%) were prepared by impregnation of NaY, HY, and HUSY zeolites using a niobum(V) ammonium oxalate complex. These obtained Nb-containing catalysts were calcined and thoroughly characterized by different physico-chemical techniques. The characterization results revealed that niobium oxide was successfully loaded on the surface of the zeolite supports without any significant modification of the faujasite structure. Surface area and pore volume were found to decrease with the increase in the Nb content for all the prepared catalysts. The presence of Nb was proved to increase the hydrophobicity of the zeolites and to affect surface acidity. The catalytic activity of the Nb-containing samples was evaluated in the glycerol acetalization reaction, and the Nb-HUSY catalysts were found to show the best catalytic performance.A. Araujo and C. Ferreira thank the ERASMUS program for their grants. This work has been developed under the scope of the project BioTecNorte (operation NORTE-01-0145-FEDER-000004) supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund. This work has also been financed by national funds (FCT, Fundacao para a Ciencia e a Tecnologia.), through the projects PTDC/AAGTEC/5269/2014 and Center of Chemistry (UID/QUI/00686/2013 and UID/QUI/0686/ 2016). The authors also acknowledge funding from Spanish Ministry project CTQ2014-57578-R and CTM2017-82335-R and Comunidad de Madrid Alccones, S2013/MAE-2985.info:eu-repo/semantics/publishedVersio

Catalysis by basic carbons: Preparation of dihydropyridines

The condensation of benzaldehyde and different substituted benzaldehydes, such as 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, and 2,4-dichlorobenzaldehyde, with ethyl cyanoacetate was carried out using two alkaline carbons (Na-Norit and Cs-Norit) as catalysts in the absence of solvent. The reaction products are precursors in the production of 1,4-dihydropyridine derivatives, which have expanding practical applications as pharmaceuticals in the line of calcium channel blockers. High values of activity and selectivity were obtained. The most active carbon (Cs-Norit), which contains basic sites with pKb = 11.2, is more active than pyridine, and less than piperidine. The selectivity to the desired condensation product when using these activated carbons is, at least, as high as in the case of the homogeneous catalyst. This "green" and "clean" method (alkaline doped carbon catalyst in the absence of solvent) can be extended to the preparation of other intermediates with medical applications.E.P.R. thanks the University of Carabobo (Venezuela) for a PhD fellowship. V.C.C. thanks the Universidad Nacional de Educación a Distancia for a PhD Fellowship. Financial support of this work by Spanish CICYT (Project CTQ2004-00243/PPQ) is gratefully acknowledged. Norit pristine carbon has been kindly supplied by Norit Company