Catalizadores ácidos basados en Nb2O5 para procesos sostenibles en biorrefinerías: producción de biodiésel, acroleína y furfural

En la actualidad, se pretende sustituir gran parte del consumo energético mundial basado en los combustibles fósiles por energía procedente de fuentes renovables. En este sentido, el uso de la biomasa como energía alternativa resulta muy interesante ya que a partir de ella pueden obtenerse tanto biocombustibles como productos de alto valor añadido, llevándose a cabo estas transformaciones en las biorrefinerías, en las que encontramos distintas plataformas, como son la plataforma oleoquímica y la plataforma de azúcares. En la plataforma oleoquímica, se obtiene principalmente biodiésel mediante la transesterificación de aceites vegetales con un alcohol de cadena corta, que suele ser metanol. Aunque actualmente se emplean catalizadores homogéneos básicos a nivel industrial para esta reacción, no son adecuados cuando el aceite de partida contiene agua y/o ácidos grasos libres, ya que se produce la formación de jabones que dificultan la separación del biodiésel y que encarece el proceso. Por tanto, resulta necesario el desarrollo de catalizadores sólidos ácidos que permitan solucionar estos inconvenientes y que puedan además reutilizarse. Asimismo, en el proceso de producción de biodiésel se obtiene glicerol como subproducto, por lo que debido al incesante aumento de la producción de biodiésel en los últimos años, se están generando gran cantidad de excedentes de glicerol. Así, es necesaria la valorización del glicerol, el cual puede transformarse a productos de alto valor añadido como la acroleína. La acroleína es un producto químico muy versátil en la industria química y puede obtenerse mediante la deshidratación de glicerol en presencia de un catalizador ácido. Por otro lado, en la plataforma de azúcares de una biorrefinería pueden producirse una gran variedad de productos químicos, entre los que destaca el furfural debido a la gran variedad de aplicaciones industriales que presenta y a la gran cantidad de productos que pueden obtenerse a partir de él. El furfural se produce mediante la deshidratación de D-xilosa en presencia de un catalizador ácido. Por lo tanto, es necesario el desarrollo de nuevos catalizadores sólidos ácidos para estos procesos de conversión de biomasa. Recientemente, el interés en catalizadores basados en óxido de niobio se ha incrementado, ya que presenta importantes propiedades ácidas y es insoluble en agua. Sin embargo, el Nb2O5 posee una baja área superficial, por lo que es interesante soportarlo sobre otros materiales con mayor superficie específica o sintetizar un óxido de niobio mesoporoso, para incrementar el número de sitios activos disponibles. En consecuencia, el principal objetivo de la presente Tesis Doctoral es la síntesis y caracterización de catalizadores basados en Nb2O5 y el estudio de su actividad catalítica en la producción de biodiésel a partir de aceite de girasol, en la deshidratación de glicerol a acroleína y la deshidratación de D-xilosa a furfural, ya que se ha expuesto que estas reacciones requieren la presencia de un catalizador ácido. Así, se han preparado distintos catalizadores basados en Nb2O5 soportado sobre materiales mesoporosos e, incluso, un Nb2O5 mesoporoso, y se ha comprobado que la acidez de los catalizadores depende del contenido en Nb2O5 y que, aunque el óxido de niobio se considera un sólido ácido de tipo Lewis, se generan centros ácidos de Brönsted cuando se soporta sobre sílice o sobre alúmina. Asimismo, se ha demostrado que estos catalizadores son activos en las reacciones estudiadas, obteniéndose rendimientos interesantes en los productos deseados (95% en biodiésel en presencia de un catalizador basado en un 8% Nb2O5 sobre una sílice mesoporosa tipo MCM-41, 45.8% en acroleína con un catalizador con un 8% Nb2O5 sobre una sílice mesoporosa tipo SBA-15 dopada con circonio y tratado con H3PO4, 72% en furfural en presencia de un catalizador basado en un 16% Nb2O5 sobre una sílice mesoporosa tipo SBA-15)

Hydrogenation of furfural over supported Pd catalysts

Lignocellulosic biomass is the most abundant and economical non-fossil carbon source. Furthermore, it is not competitive with the food chain, coming from lignocellulosic wastes including agricultural and food processing, local urban solid and forestry wastes. However, these are made up of complex carbohydrates (mainly, cellulose and hemicellulose), which require to be broken down in their respective monomers. The hemicellulose is mainly composed of pentosans, which, after an initial hydrolysis step, are dehydrated to furfural. Furfural is an important platform molecule, since it has a wide range of applications, being considered the main chemical, aside from bioethanol, obtained from the sugar platform for the synthesis of chemicals, for plastics, agrochemical and pharmaceutical industries. In the present work, the hydrogenation of furfural in gas phase has been studied by using Pd as active phase, and different metal oxides as support, in order to elucidate the influence of the support on the catalytic performance. Furfural can be converted into chemicals with important applications in many different industrial fields. Thus, reduction of furfural can proceed through different pathways depending on the experimental conditions, where the nature of the catalysts plays a key role. In the case of Pd-based catalysts, the main products come from the decarbonylation of furfural.The catalytic results reveals that the nature of the support exerts an important influence on furfural conversion and yield. The highest conversion (92% after 5 h of TOS at 463 K) was attained with a Pd-SiO2 catalyst, with a furan yield of 70 mol%. This catalyst is the most selective to furan and a moderate deactivation is only observed after 5 h reaction. The catalytic performance demonstrates that decarbonylation reaction was the main pathway, although the formation of furfuryl alcohol and 2-methylfuran also suggests that the hydrogenation of the carbonyl group of furfural takes place.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

γ-Al2O3 as acid catalyst for dehydration of glucose to 5-hydroxymethylfurfural

Currently, the search and development of sustainable feedstocks for chemicals derived from petrol have gained worldwide attraction because of the instability of the price of crude oil, the reduction of fossil oil reserves, and the environmental concerns associated to the greenhouse effect caused by CO2 emissions, being biomass one of the world’s most important renewable carbon sources. The major component of plant-derived biomass are carbohydrates, being of great importance to develop efficient and green approaches to their valorization by conversion into high value-added products. Thus, glucose can be transformed by dehydration into 5-hydroxymethylfurfural (HMF), which is a versatile and key intermediate for the production of a wide variety of biobased chemicals and it is attracting much attention in biofuels and chemical industry. Different catalytic systems have been evaluated for HMF production from C6 carbohydrates as glucose, mostly based on heterogeneous catalysis as alternative to the use of liquid mineral acids. On the other hand, the high surface area, large pore size and thermal and hydrothermal stabilities of some mesoporous solids make them suitable for many catalytic processes. In the present work, the dehydration of glucose to HMF has been evaluated by using different mesoporous γ-Al2O3 with acid, neutral or basic character, in a biphasic water–MIBK solvent system to avoid the HMF degradation and its possible reaction with the intermediates from glucose to give soluble polymers and humins or acetalization with glucose. Different experimental parameters, such as reaction temperature and time, as well as the addition of inorganic salts have been studied in order to reach the maximum HMF yield.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Ministry of Economy and Competitiveness (CTQ2012-38204-C04-02 project), Junta de Andalucía (RNM-1565) and FEDER fund

One-pot synthesis of green-emitting nitrogen-doped carbon dots from xylose

Carbon dots (CDs) are interesting carbon nanomaterials that exhibit great photoluminescent features, low cytotoxicity, and excellent water stability and solubility. For these reasons, many fields are starting to integrate their use for a variety of purposes. The catalytic performance of VOPO4 has been evaluated in the synthesis of nitrogen-doped carbon dots (N-CDs). The synthesis reaction was carried out at 180 °C using VOPO4 as a heterogeneous catalyst for 2 to 4 h of reaction time. After reaction, the N-CDs were purified using a novel method for the protection of the functional groups over the surfaces of the N-CDs. The morphological, superficial, and photoelectronic properties of the N-CDs were thoroughly studied by means of TEM, HRTEM, XPS, and photoluminescence measurements. The conversion of the carbon precursor was followed by HPLC. After three catalytic runs, the catalyst was still active while ensuring the quality of the N-CDs obtained. After the third cycle, the catalyst was regenerated, and it recovered its full activity. The obtained N-CDs showed a great degree of oxidized groups in their surfaces that translated into high photoluminescence when irradiated under different lasers. Due to the observed photoelectronic properties, they were then assayed in the photocatalytic degradation of methyl orange.This research was funded by the Spanish Ministry of Science and Innovation (PID2021-122736OB-C42, PID2021-122613OB-I00) and FEDER (European Union) funds (PID2021-122736OB-C42, P20-00375, UMA20-FEDERJA88)

Mesoporous niobium oxide for dehydration of D-xylose into furfural

Se ha demostrado que el óxido de niobio mesoporoso es un catalizador eficaz para la deshidratación de D-xilosa a furfural, alcanzando una conversión del 92% y un rendimiento de furfural 49,3% a 170º C y 90 minutos. La lixiviación de Nb, determinada por ICP-MS, era inferior al 0,5% en peso de la concentración de Nb inicial, confirmando de este modo la estabilidad del catalizador ácido sólido.El furfural posee un gran potencial como molécula plataforma de origen renovable para la síntesis de una alta variedad de compuestos químicos. Se obtiene mediante la deshidratación de pentosas, principalmente a partir de D-xilosa, proceso catalizado por ácidos minerales en fase homogénea. Por tanto, dentro de la química verde y la búsqueda de sostenibilidad de los procesos catalíticos, es necesaria su sustitución por catalizadores sólidos ácidos que sean tolerantes al agua, ya que es el disolvente más utilizado para esta reacción. El óxido de niobio posee propiedades ácidas y es insoluble en agua, pero su superficie específica es muy baja. Por lo tanto, resulta muy interesante la síntesis de un óxido de niobio mesoporoso para emplearlo como catalizador en esta reacción. En este trabajo, se ha sintetizado un Nb2O5 mesoporoso y se ha evaluado su comportamiento catalítico en la obtención de furfural a partir de D-xilosa.Spanish Ministry of Science and Innovation (ENE2009-12743-C04-03 project)Junta de Andalucía (P09-FQM-5070).Ministry of Science and Innovation for the financial support under the Program Ramón y Cajal (RYC-2008-03387)

Epidemiología molecular de enterobacterias productoras de carbapenemasas

En los últimos años se está observando un incremento de bacterias multirresistentes gramnegativas portadoras de genes codificantes de carbapenemasas. La emergencia de enterobacterias productoras de carbapenemasas como causa de infecciones es un asunto de gran preocupación, y la evolución futura indica un aumento de estas infecciones, tanto nosocomiales como adquiridas en la comunidad. Además, la inclusión de estos genes en elementos genéticos móviles (integrones, plásmidos) puede estar favoreciendo su diseminación entre diferentes géneros y especies bacterianas. El objetivo principal de este estudio es conocer cuál es la situación en el Sector Sanitario de Zaragoza III en cuanto a la prevalencia en muestras clínicas y caracterizar los mecanismos de resistencia a β-lactámicos, con especial atención a la producción de carbapenemasas, así como su posible asociación con mecanismos de resistencia a otras familias de antimicrobianos como aminoglucósidos y quinolonas. Para ello, se ha realizado un estudio entre Abril de 2012 y Agosto de 2014 en el Servicio de Microbiología del Hospital Clínico Universitario Lozano Blesa en el que se han seleccionado cepas de enterobacterias procedentes de muestras clínicas con un perfil de sensibilidad compatible de ser portadoras de carbapenemasas. En estos aislados se ha estudiado la sensibilidad a diferentes antibióticos para orientar los posibles mecanismos de resistencia responsables de dicho patrón de sensibilidad. A su vez, se han realizado diferentes test fenotípìcos para clasificar las enterobacterias como posibles cepas portadoras de β-lactamasas tipo BLEEs, AmpC y carbapenemasas. Posteriormente, se han caracterizado los mecanismos implicados en la resistencia a distintos antimicrobianos mediante métodos moleculares, principalmente los asociados con el fenotipo BLEE, AmpC y carbapenemasa. En las cepas portadoras de carbapenemasas se determinó la presencia de los integrones tipo 1, 2 y 3, así como las resistencias asociadas a antibióticos no β-lactámicos (quinolonas y aminoglucósidos)

Plasma-Induced Defects Enhance the Visible-Light Photocatalytic Activity of MIL-125(Ti)-NH2 for Overall Water Splitting

This is the peer reviewed version of the following article: M. Cabrero-Antonino, J. Albero, C. García-Vallés, M. Álvaro, S. Navalón, H. García, Chem. Eur. J. 2020, 26, 15682, which has been published in final form at https://doi.org/10.1002/chem.202003763. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] Defect engineering in metal-organic frameworks is commonly performed by using thermal or chemical treatments. Herein we report that oxygen plasma treatment generates structural defects on MIL-125(Ti)-NH2, leading to an increase in its photocatalytic activity. Characterization data indicate that plasma-treated materials retain most of their initial crystallinity, while exhibiting somewhat lower surface area and pore volume. XPS and FT-IR spectroscopy reveal that oxygen plasma induces MIL-125(Ti)-NH2 partial terephthalate decarboxylation and an increase in the Ti-OH population. Thermogravimetric analyses confirm the generation of structural defects by oxygen plasma and allowed an estimation of the resulting experimental formula of the treated MIL-125(Ti)-NH2 solids. SEM analyses show that oxygen plasma treatment of MIL-125(Ti)-NH2 gradually decreases its particle size. Importantly, diffuse reflectance UV/Vis spectroscopy and valence band measurements demonstrate that oxygen plasma treatment alters the MIL-125(Ti)-NH2 band gap and, more significantly, the alignment of highest occupied and lowest unoccupied crystal orbitals. An optimal oxygen plasma treatment to achieve the highest efficiency in water splitting with or without methanol as sacrificial electron donor under UV/Vis or simulated sunlight was determined. The optimized plasma-treated MIL-125(Ti)-NH2 photocatalyst acts as a truly heterogeneous photocatalyst and retains most of its initial photoactivity and crystallinity upon reuse.S.N. thanks the Fundacion Ramon Areces (XVIII Concurso Nacional para la Adjudicacion de Ayudas a la Investigacion en Ciencias de la Vida y de la Materia, 2016), the Ministerio de Ciencia, Innovacion y Universidades RTI 2018-099482-A-I00 project, the Generalitat Valenciana grupos de investigacion consolidables 2019 (ref: AICO/2019/214) project, and the AVI project (INNEST/2020/111) for financial support. Financial support by the European Union (LoterCO2M), Spanish Ministry of Science, Innovation and Universities (Severo Ochoa and RTI2018-098237-B-C21), and Generalitat Valenciana (Prometeo 2017-083) is also gratefully acknowledged.Cabrero-Antonino, M.; Albero-Sancho, J.; García-Vallés, C.; Alvaro Rodríguez, MM.; Navalón Oltra, S.; García Gómez, H. (2020). 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N-Doped graphene as a metal-free catalyst for glucose oxidation to succinic acid

[EN] N-Containing graphenes obtained either by simultaneous amination and reduction of graphene oxide or by pyrolysis of chitosan under an inert atmosphere have been found to act as catalysts for the selective wet oxidation of glucose to succinic acid. Selectivity values over 60% at complete glucose conversion have been achieved by performing the reaction at 160 degrees C and 18 atm O-2 pressure for 20 h. This activity has been attributed to graphenic-type N atoms on graphene. The active N-containing graphene catalysts were used four times without observing a decrease in conversion and selectivity of the process. A mechanism having tartaric and fumaric acids as key intermediates is proposed.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, Grapas and CTQ2015-69153-CO2-R1) and Generalitat Valenciana (Prometeo 2013-014) is gratefully acknowledged. Prof. Simona M. 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Catalytic Activity of Mixed Al2O3-ZrO2 Oxides for Glucose Conversion into 5-Hydroxymethylfurfural

In the present work, a series of catalysts based on aluminum and zirconium oxides was studied for the transformation of glucose into 5-hydroxymethylfurfural. These catalysts were characterized by using experimental techniques, such as X-ray diffraction, N2 adsorption–desorption at -196 ºC, X-ray photoelectron spectroscopy, temperature-programmed desorption of NH3 and CO2, and scanning transmission electron microscopy. The catalytic behavior in glucose dehydration was evaluated in a water-methyl isobutyl ketone biphasic system, in the presence of CaCl2, in order to minimize losses due to unwanted secondary reactions. High glucose conversion and 5-hydroxymethylfurfural (HMF) yield values were obtained in the presence of an Al(Zr)Ox catalyst with an Al:Zr molar ratio of 7:3, reaching 97% and 47%, respectively, at 150 ºC after 120 min. Under tested conditions, this catalyst retained most of its catalytic activity for four reuses.This research was funded by the Spanish Ministry of Economy and Competitiveness (RTI2018-94918-B-C44), FEDER (European Union) funds (UMA18-FEDERJA-171) and Malaga University

Selective production of furan from gas-phase furfural decarbonylation on Ni-MgO catalysts.

A series of Ni-MgO catalysts (Ni/Mg molar ratio: 0.1-0.3), prepared by a coprecipitation-calcination-reduction methodology, was characterized and evaluated in the gas-phase hydrogenation of furfural. In all cases, after reduction at 500ºC, nickel species were present as very tiny metal Ni(0) nanoparticles and forming part as Ni(II) of a NiO-MgO solid solution, as inferred from XRD and XPS techniques. The decarbonylation process of furfural was favoured at reaction temperatures as low as 190ºC. The most active catalyst was that with a Ni/Mg molar ratio of 0.25, maintaining a furfural conversion of 96% after 5 h of time-on-stream at 190ºC, by feeding a furfural solution in cyclopentylmethyl ether (5 vol.% furfural) under a H2 stream (H2:furfural molar ratio= 11.5 and WHSV= 1.5 h-1). Furan was the main product, with a yield of 88%, whereas furfuryl alcohol was formed at lower reaction temperature and shorter contact time. However, the catalyst suffers a gradual deactivation during a catalytic test of 24 h, attaining a FUR conversion of 65%, with a furan yield following a similar trend (55%), while FOL was almost negligible (only 6%). The regeneration after calcination led to the sintering of Ni nanoparticles, thus decreasing the furan yield.Spanish Ministry of Economy and Competitiveness (CTQ2015-64226-C03-3-R project), Junta de Andalucía (RNM-1565) and FEDER (European Union) funds. J.A.C. and C.G.S. thank University of Malaga for contracts of PhD incorporation. R.M.T. thanks to the Spanish Ministry of Economy and Competitiveness (IEDI-2016-00743) for the financial support within the I3 program