Nanopartículas soportadas sobre materiales porosos para la síntesis de productos de alto valor añadido

Las investigaciones se han focalizado, en primer lugar, en el desarrollo de sistemas de nanopartículas de CdS soportadas sobre biopolímeros (almidón y quitosano) con el objeto de desarrollar nuevos sistemas con propiedades fotocatalíticas y optoelectrónicas. Asimismo, se han sintetizado sistemas bifuncionales de nanopartículas de óxido de hierro soportadas sobre materiales ácidos Al-MCM-41 y Al-SBA-15, mostrandos unas interesantes actividades catalíticas en procesos de oxidación de alcoholes. Con el objeto de extender estos estudios a reacciones de tipo tándem promovidas por centros ácidos y metálicos se han desarrollado sistemas de nanopartículas metálicas de Pd, Pt y Cu sobre alumino- y galosilicatos MCM-41 y SBA-15 se han aplicado a la producción de mentol a partir de citronelal mediante un proceso tándem de ciclación/hidrogenación asistido por microondas. Dicha reacción puede llevarse a cabo utilizando compuestos racémicos o enantioméricamente puros, obteniéndose en todos casos unas conversiones completas con selectividades superiores al 65% en todos los casos a mentol racémico o a (+)¿mentol a partir de (-)-citronelal utilizando modificadores quirales. Finalmente, se han investigado la presencia de efectos de microondas en la síntesis de los sistemas óxido de hierro/silicato, obteniéndose que independientemente de la temperatura, la rampa de calentamiento y la agitación (que son por otra parte los tres parámetros principales a controlar en la síntesis de dichos materiales), no existen efectos de microondas en los sistemas y por tanto las diferencias observadas entre los materiales obtenidos mediante síntesis asistida por microondas y aquellos obtenidos mediante calentamiento convencional se deben a un puro efecto térmico de la rapidez y la eficiencia del calentamiento con microondas en comparación con el calentamiento convencional

Efficient and environmentally friendly microwave-assisted synthesis of catalytically active magnetic metallic Ni nanoparticle

Pure magnetic metallic nickel was synthesized by a simple and fast microwave-assisted method using a monomode microwave reactor. Nickel chloride was employed as metal precursor, while an environmental-friendly mixture of ethylene glycol and ethanol was simultaneously used as solvent and reducing agent. The parameters combination, for the occurrence of the reaction, of the mixture molar fraction, and the metal precursor concentration was developed. The influence of the temperature and the time of the irradiation was investigated. The best performance (71% yield) was achieved at 250 °C in 5 min of microwave irradiation. The phase and the morphology of the metal were analyzed by X-ray diffraction, scanning emission microscopy, and transmission electron microscopy, while the surface area was determined by nitrogen physisorption. The material exhibited a strong magnetic behavior. The metallic nickel showed high catalytic activity for the hydrogenolysis of benzyl phenyl ether, a lignin model compound, in a microwave-assisted environmental-friendly reaction

Catalytic Conversion of Biomass

Petroleum, natural gas and coal supply most of the energy consumed worldwide and their massive utilization has allowed our society to reach high levels of development in the past century. The shift towards a bio-based economy has been recently promoted with ambitious targets to replace an important fraction of fossil fuels by renewable sources within 20 years. Biomass emerged as a highly suitable alternative for this bio-based revolution as an ideal substitute for petroleum in the production of fuels, chemicals and carbon-based materials. Consequently, a number of ongoing efforts have been devoted to biomass conversion/valorization towards valuable products using a number of (bio)catalytic strategies. Based on these premises, the present Special Issue of Catalysts was aimed to provide a number of broad and multifaceted contributions in the field of catalytic biomass conversion towards the production of high added value products from sugars (hemicellulose and cellulose fraction) and lignin as well as related biomass conversion strategies. In this regard, Song et al. contributed to develop an efficient dehydration of fructose to HMF using heteropolyacid salts [1]. Along similar lines, two additional contributions for the Special Issue from Li et al. [2] and Fachri et al. [3] disclosed the catalytic aqueous conversion of glucose and inulin into HMF using Lewis acid and metal salts catalysts, respectively, providing also interesting modelling insights into the proposed chemistries. The produced furanic derivatives in these contributions as well as related compounds (e.g., sorbitol) have also promising prospects to be further upgraded to fuel components for blends. Pizzi et al. provided a nice approach towards high throughput screening of a range of heterogeneous catalysts for the conversion of furfural to bio-based fuel components [4] in a similar way to the approach proposed by Iglesias et al. for the conversion of furfural to furfuryl alcohol via Meerwein-Ponndorf-Verley reduction using Zr-SBA-15 [5], while valuable jet-fuel range hydrocarbons could also be produced from biomass-derived sorbitol using Ni-HZSM-5/SBA-15 catalysts [6]. Such biomass-engineered products have a significant potential to replace current petroleum-derived analogues with improved biocompatibility and a reduced environmental footprint. Levulinic acid and levulinates are related interesting platform molecules that can be derived from biomass and subsequently upgraded towards chemicals and biofuel precursors. Along these lines, Wang et al. proposed the utilization of cheap and environmentally friendly Nb/Al oxide catalysts for the conversion of kiwifruit waste to levulinic acid [7]. Additionally, the direct conversion of carbohydrates into ethyl levulinate using potassium phosphotungstate as efficient catalyst was reported by Zhao et al. [8]. Further conversion of levulinic acid to gamma-valerolactone (GVL) could also take place efficiently on nickel/alumina catalysts [9]. Hydrogenation and hydrodeoxygenation of lignin and lignocellulosic pyrolysis has also been another hot topic in recent times due to the possibility to produce aromatics and cyclic derivatives from biomass. Yi et al. proposed a highly efficient hydrogenation of lignin derived monophenols towards cyclohexanols using Pd/alumina catalysts [10]. Co-pyrolysis behavior of cotton straw mixtures and their catalytic hydrodeoxygenation were also investigated by Hua et al. [11] using Ni-Mo/alumina catalysts. Additional contributions to the Special Issue included the selective production of aromatics from 2-octanol on Zn-exchanged MFI zeolites [12], the electrocatalytic oxidation of cellulose to gluconate on carbon aerogel supported gold nanoparticles anodes [13] and the steam reforming of bioethanol to hydrogen catalyzed by Co/ceria catalysts [14]. The Guest Editors sincerely hope that the results presented as part of this Special Issue of most varied topics can serve as a starting point for further innovations in the catalytic conversion of biomass and look forward to enjoying further improvements in the aforementioned topics and fields in the future

Heterogeneous Catalysis to Drive the Waste-to-Pharma Concept: From Furanics to Active Pharmaceutical Ingredients

A perspective on the use of heterogeneous catalysis to drive the waste-to-pharma concept is provided in this contribution based on the conversion of furanics to active pharmaceutical ingredients (APIs). The provided overview of the concept in this perspective article has been exemplified for two key molecule examples: Ancarolol and Furosemide

Sol-Gel Immobilisation of Lipases: Towards Active and Stable Biocatalysts for the Esterification of Valeric Acid

Alkyl esters are high added value products useful in a wide range of industrial sectors. A methodology based on a simple sol-gel approach (biosilicification) is herein proposed to encapsulate enzymes in order to design highly active and stable biocatalysts. Their performance was assessed through the optimization of valeric acid esterification evaluating the effect of different parameters (biocatalyst load, presence of water, reaction temperature and stirring rate) in different alcoholic media, and comparing two different methodologies: conventional heating and microwave irradiation. Ethyl valerate yields were in the 80–85% range under optimum conditions (15 min, 12% m/v biocatalyst, molar ratio 1:2 of valeric acid to alcohol). Comparatively, the biocatalysts were slightly deactivated under microwave irradiation due to enzyme denaturalisation. Biocatalyst reuse was attempted to prove that good reusability of these sol-gel immobilised enzymes could be achieved under conventional heating