Influencia de la presencia de compuestos superficiales de P sobre la funcionalización de carbones activos con HNO3

La funcionalización con ácido nítrico es un método ampliamente estudiado para la incorporación de grupos funcionales de oxígeno en la superficie de carbones activos, tales como grupos carboxilos, anhídridos, lactonas y fenoles. Sin embargo, también incorpora, en menor medida, grupos funcionales nitrogenados. Estos grupos funcionales de N son capaces de mejorar las propiedades de adsorción y/o catalíticas de diferentes carbones activos. Por otro lado, la activación química con ácido fosfórico produce carbones activos con una cantidad importante de grupos superficiales de fósforo de gran estabilidad, que les confiere una elevada resistencia a la oxidación y acidez, que los hace muy interesantes en diferentes aplicaciones catalíticas. En este trabajo se va a estudiar la influencia de la presencia de estos grupos de fósforo en la funcionalización de carbones activos con ácido nítrico.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Funcionalización superficial de carbones activos con grupos nitrogenados mediante reaciones de oxidación/reducción

La funcionalización superficial de carbones activos con grupos nitrogenados le confiere a estos materiales unas propiedades fisicoquímicas mejoradas, que los hace muy interesantes en diferentes aplicaciones. La incorporación de heteroátomos de nitrógeno a materiales carbonosos ser realiza principalmente mediante dos estrategias: partiendo de precursores que contengan nitrógeno y mediante tratamientos químicos de funcionalización con moléculas nitrogenadas, tales como amoniaco o urea [2]. En este trabajo se ha estudiado la funcionalización superficial, con diferentes grupos nitrogenados, de carbones activos obtenidos por activación química con ácido fosfórico. La incorporación de nitrógeno se ha llevado a cabo mediante un tratamiento con ácido nítrico, realizándose a continuación diferentes tratamientos de reducción, con el fin de obtener diferentes grupos funcionales de nitrógeno.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

VPO catalysts using activate carbons as template. ODH of propane

Resumen comunicación a congreso internacionalVanadium phosphates is one of the most studied heterogeneous catalytic systems due to its properties to activate alkanes. In fact, they are used commercially for the oxidation of n-butane to maleic anhydride and experimental studies have shown that vanadium phosphates are also effective catalysts for propane and pentane partial oxidation. The most active phase of VPO catalysts is made up of a well-crystallized (VO)2P2O7, which is considered to possess unique structural and surface features to allow the activation of alkanes. This phase is generally generated by calcination of the precursor VOHPO4·0.5H2O. A new strategy to obtain this precursor has been analyzed in this study. The proposed methodology is simple and low cost and implies the use of a carbon material as a template to obtain the mixed oxide with a developed porous structure. Several VPO catalysts were prepared by using different activated carbons, which were obtained from lignocellulosic waste, as template. The carbonaceous materials were obtained by chemical activation with phosphoric acid of olive stones and by liquid phase impregnation of zeolite templates with lignin solution. Both porous carbons were impregnated with a solution containing the dissolved vanadium phosphate precursor. This solution was prepared by mixing water with ammonium metavanadate, phosphoric acid and oxalic acid in the precise amounts to obtain a V/P atomic ratio of 1. Finally, in order to remove the carbonaceous matrix and to obtain the active phase (VO)2P2O7, the impregnated samples were calcined in air at 500 ºC for 6 h. The presence of the desired active phase (VO)2P2O7 was confirmed by using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and X-ray diffraction (XRD). The porous structure was characterized by N2 adsorption-desorption at -196 ºC. Catalytic tests were performed in a fixed bed microreactor under a gas flow mixture (W/F = 0,075 g·s·mL-1) containing propane, oxygen and helium (45.7/11.4/42.9 vol. %). The reaction was studied at different temperatures from 500 to 575 ºC. The use of a carbon as a template results in VPO catalysts with relatively high development of the porous structure (apparent surface area of 40 m2/g), compared to those reported in the literature. These catalysts present propane conversions up to 22 % with selectivities to propylene as high as 60 %. It is noteworthy that selectivities to ethylene about 25% were also observed, which is a highly valued product in the chemical industry. These results are comparable to those reported in the literature for supported vanadium oxides at higher space times.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Estudio cinético de la reacción de ODH de propano sobre catalizadores de vanadio electrohilado con tamaño submicrométrico

Fecha de lectura de Tesis Doctoral: 4 de febrero 2020El propileno es el segundo compuesto más utilizado en la industria química. El incremento de la demanda ha incentivado la aparición de tecnologías alternativas para producir propileno. La deshidrogenación oxidativa (ODH) de propano para obtener propileno aparece como una alternativa prometedora para superar todas las limitaciones que sufren los procesos comerciales actuales. Se ha estimado que se podría reducir hasta un 45% el consumo de energía, dado que es un proceso exotérmico que funciona a temperaturas significativamente más bajas. Además, la reacción no está termodinámicamente restringida y la desactivación del catalizador por deposición de coque es prácticamente inexistente. Sin embargo, la ODH de propano no ha sido industrialmente implementada todavía debido a que los rendimientos y/o productividades hacia propileno obtenidos con este proceso actualmente son bajos. La presente tesis doctoral ha abordado tres objetivos generales: 1. La preparación de catalizadores para la ODH de propano en forma de fibra con diámetro submicrométrico y basados en óxidos mixtos de Zr, V, Mo y/o Nb mediante la técnica de electrospinning. 2. El estudio del mecanismo de la reacción y el entendimiento de la relación que hay entre la actividad y la estructura del catalizador. Para ello se ha utilizado por primera vez un reactor operando hecho a mano, que permite medir la actividad catalítica del catalizador, y de forma simultánea caracterizar su superficie mediante espectros infrarrojos y Raman. 3. El estudio cinético de la reacción para obtener información cinética de las distintas especies activas y para simular valores de rendimiento y productividad analizando su dependencia. De forma que se puedan optimizar las condiciones de operación para obtener el rendimiento y/o productividad máximo posible y conocer el verdadero potencial de los catalizadores, lo cual es importante para estudiar la viabilidad económica de su implementación en la industria

Unraveling the propane ODH mechanism by simultaneous FTIR Raman operando studies over VOX/SrO2 catalysts

International audienc

Operando Reactor-Cell with Simultaneous Transmission FTIR and Raman Characterization (IRRaman) for the Study of Gas-Phase Reactions with Solid Catalysts

International audienceRaman and transmission FTIR spectroscopic techniques have been coupled in a new homemade reactor-cell designed in a joint CSIC-LCS collaboration. The setup is easily adapted to any FTIR and fiber-coupled Raman spectrometers and gas analysis techniques. It allows for simultaneous operando FTIR and Raman spectroscopic measurement, which provide complementary characterization of adsorbed species, reaction intermediates, and structural properties of the catalyst. This system was validated with the study of vanadium-based catalysts during propane oxydehydrogenation (ODH). The combined use of both spectroscopies with gas analysis techniques to measure the activity contributes to the understanding of propane ODH and the identification of the role of different oxygen species bound to vanadium sites. For example, the simultaneous characterization of the catalyst under the same conditions by IR and Raman confirms that the V=O mode has the same frequency in both spectroscopies and that bridging oxygen sites (V-O-V, V-O-Zr) present higher activity than terminal V=O bonds. These results demonstrate the high potential of the new simultaneous transmission IR-Raman operando rig to correlate the activity and the structure of catalysts, thus assisting the rational design of catalytic processe

Operando Reactor-Cell with Simultaneous Transmission FTIR and Raman Characterization (IRRaman) for the Study of Gas-Phase Reactions with Solid Catalysts

Raman and transmission FTIR spectroscopic techniques have been coupled in a new homemade reactor-cell designed in a joint CSIC-LCS collaboration. The setup is easily adapted to any FTIR and fiber-coupled Raman spectrometers and gas analysis techniques. It allows for simultaneous operando FTIR and Raman spectroscopic measurement, which provide complementary characterization of adsorbed species, reaction intermediates, and structural properties of the catalyst. This system was validated with the study of vanadium-based catalysts during propane oxydehydrogenation (ODH). The combined use of both spectroscopies with gas analysis techniques to measure the activity contributes to the understanding of propane ODH and the identification of the role of different oxygen species bound to vanadium sites. For example, the simultaneous characterization of the catalyst under the same conditions by IR and Raman confirms that the V═O mode has the same frequency in both spectroscopies and that bridging oxygen sites (V - O - V, V - O - Zr) present higher activity than terminal V═O bonds. These results demonstrate the high potential of the new simultaneous transmission IR-Raman operando rig to correlate the activity and the structure of catalysts, thus assisting the rational design of catalytic processes.Authors acknowledge the FEDER-Region Basse-Normandie (France)-CNRS for a Chaire d’Excellence, which resulted in the implementation of the “IRRaman” rig and a research stay allowing for the performance of these investigations. This work was also supported by the Spanish Ministry of Economy and Competitiveness and FEDER (CTQ2012-36408, CTQ2015-68654-R, and CTM2017-82335-R). J.J.T.H. acknowledges the assistance of the Ministry of Economy and Competitiveness of Spain for the award of a FPI Grant (BES-2013-064425) and the award for performing his stay at ENSICAEN (EEBB-I-16-10749)

Fixing PAN Nanofiber Mats during Stabilization for Carbonization and Creating Novel Metal/Carbon Composites

Polyacrylonitrile (PAN) is one of the materials most often used for carbonization. PAN nanofiber mats, created by electrospinning, are an especially interesting source to gain carbon nanofibers. A well-known problem in this process is fixing the PAN nanofiber mats during the stabilization process which is necessary to avoid contraction of the fibers, correlated with an undesired increase in the diameter and undesired bending. Fixing this issue typically results in breaks in the nanofiber mats if the tension is too high, or it is not strong enough to keep the fibers as straight as in the original state. This article suggests a novel method to overcome this problem by electrospinning on an aluminum substrate on which the nanofiber mat adheres rigidly, stabilizing the composite and carbonizing afterwards either with or without the aluminum substrate to gain either a pure carbon nanofiber mat or a metal/carbon composite