Alcohol decomposition on basic/acid lignin-derived submicron diameter carbon fibers

The use of lignin, the second most abundant polymer in nature, along with a simple and versatile technique, electrospinning, represents an advantageous and promising approach for the preparation of carbon fibers. In previous studies, we have demonstrated that the incorporation of H3PO4 to the initial lignin solution allows for shortening the carbon fibers preparation process and that the resulting carbon fibers present P-surface groups that are of great interest for heterogeneous catalysis. Different carbon fibers catalysts have been prepared by electropinning of Alcell lignin in the absence or presence of H3PO4 as chemical activating agent. Carbonization at different temperatures between 500 and 1600 ºC allows for preparing carbon fibers with a high variety of porosity and chemical surface properties. Diverse oxygen surface groups are presented on the carbon catalysts surface. The isopropanol decomposition has been used as a catalytic test to study the acid or basic character of the prepared carbon fibers. Carbon fibers without phosphorus surface groups generate acetone as the main product of the isopropanol decomposition reaction, from 400 to 600 ºC, suggesting the basic character of these catalysts. On the contrary, phosphorus-containing carbon fibers show high acid character, producing selectivity to propylene of 100 % at temperatures between 250 and 350 ºC. The most acid carbon fiber catalyst produced a high selectivity to ethylene and dimethyl ether for the decomposition of ethanol and methanol, respectively. The conversion enhancement that the presence of oxygen in the gas phase produced for all these reactions was also studied.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MINECO (PTA2015-11464-I)

Flexible and low-cost binderless capacitors based on p- and n-containing fibrous activated carbons from denim cloth wastes

Activated carbon cloths have been prepared from denim cloth wastes (DCWs) through chemical activation with H3PO4. The effect of the H3PO4/DCWs impregnation ratio and the carbonization temperature on the porous texture, the chemical composition, the fibers morphology, and the electrochemical performance has been studied. Low H3PO4/DCWs impregnation ratios lead to flexible and microporous activated carbons cloths, whereas more fragile and rigid activated carbon cloths with higher external surface area are produced upon increasing the amount of H3PO4. The increase in the carbonization temperature allows for obtaining a more ordered and conductive carbon structure. The activated carbon prepared at 900 ºC with a H3PO4/DCWs impregnation ratio of 0.5 (w/w) exhibits the best performance as electric double layer capacitor. This electrode shows a specific surface area of 2016 m2 g-1 and the highest registered gravimetric capacitance (227 F g-1). Moreover, its flexibility minimizes the ohmic resistance of the electrode, thus increasing the feasibility of working at higher current densities than the other synthesized electrodes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech; MINECO CTQ2015-68654-

High temperature treatments of porous activated carbon

The use of biomass waste for the preparation of activated carbon is of great industrial interest for reducing costs and increasing the sustainability, especially in the field of energy storage. A high temperature treatment is required to obtain a more ordered carbon material, thus increasing its conductivity. However, this high temperature treatment entails as a disadvantage a significant reduction in porosity. Therefore, a method to prepare activated carbons with a high porosity development as well as high conductivity could be of great interest for many applications. The aim of this work is to analyze the possible influence of phosphorus compounds on the physical-chemical properties of different carbon materials thermally treated at relatively high temperatures (1600 ºC). With this goal, it has been prepared activated carbons from different precursors (olive stone, lignin and hemp) and different conformations (powder, fibers and monoliths) by physical and chemical activation, with CO2 and H3PO4, respectively. Once the different activated carbon materials were prepared, they were thermally treated at 1600 ºC under inert atmosphere. The different samples were characterized by N2 and CO2 adsorption at 77 and 273 K, respectively, XPS, XRD and Raman techniques. The oxidation resistance was also evaluated in a thermogravimetric balance. High temperature treatments of activated carbon without the presence of P surface groups produced an important contraction of the porosity (from 900 to 150 m2 g-1). However, temperature treatments of phosphorus-activated carbon allowed for preparing carbon materials with a relatively high structural order and a well-developed porosity (c.a. 1100 m2 g-1), with a significant contribution of mesoporosity. These results suggest that these P-surface groups are responsible for the low contraction observed for the porous structure, avoiding, in a large extent, its collapse.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MINECO (PTA2015-11464-I)

Modification of the morphology, porosity and surface chemistry of lignin-based electrospun carbon materials

Lignin is a biopolymer that can be found as the main component of plants. It is obtained as a coproduct in the papermaking and biofuel industries. Owing to its high carbon and aromatic content, high availability and reduced cost, it is an excellent precursor for the preparation of highly valued carbon materials. Electrospinning is a suitable top-down technique for the preparation of polymeric fibers using high voltage electrical fields and polymer solutions of proper viscosity and conductivity. Organosolv lignins, which are extracted from lignocellulosic biomass using organic solvents, are soluble in ethanol, obtaining a solution that matches the requirement of the electrospinning process. In this way, it is possible to produce lignin-based porous carbon fibers using a coaxial electrospinning device [1]. This contribution summarizes our findings about the preparation of carbon materials with different morphologies and composition by processing lignin using electrohydrodynamic forces. Lignin spheres, beaded fibers, straight fibers, beaded tubes and straight tubes are obtained by using coaxial and triaxial spinnerets that allows the electrospinning of two or three different solutions at once [1], Fig. 1. Thermal stabilization in air is needed in order to avoid melting of lignin fibers during carbonization. Stabilization times of 48-96 hours are usually required in this step, decreasing the sustainability of the production process. Phosphoric acid can be added in small amounts in the lignin solution, shortening the time for achieve a successful thermostabilization of the fiber [2]. The carbonized materials show narrow microporosity and large surface area values (SBET from 600 to 1000 m2g-1) and additional pore size and volume can be developed by controlled gasification.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER (CTQ-2015-68654-R)

Activated carbons as catalytic support for Cu nanoparticles

There are a wide range of catalytic applications for Cu-based nanoparticles materials, since Cu is an abundant and inexpensive metal and Cu nanoparticles possess unusual electrical, thermal and optical properties. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. A previous work have explored the possibilities of SBA-15 (1,2) as support for Cu nanoparticles. In the present contribution, those results will be compared with the use of a carbon material as support, since activated carbon present many advantages with respect SBA, as the high surface area.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

One-pot synthesis of lignin-based electrospun oxygen reduction reaction electrocatalysts

Owing to their adequate combination of high surface area, electrical conductivity and electrochemical resistance, carbon fibers has been used for a long time as a catalyst supports and gas diffusion layers in the electrodes of fuel cells. However, the use of high amounts of noble metals in the cathode is hampering the commercial utilization of fuel cells. We have recently demonstrated that the electrospinning of lignin, a widely available and non-expensive biopolymer, allows the production of porous carbon cloths, which have been already utilized as electrodes for methanol oxidation and supercapacitors. In this work, we propose the electrospinning of lignin and noble/non-noble metal precursors for one-pot production of ORR catalysts. Fe, Co, Pd and Pt salts have been incorporated onto lignin-ethanol solutions and have been electrospun in microsized, metal-decorated lignin fibers. The stabilization and carbonization of these fibers have produced carbon electrodes with supported metallic nanoparticles up to 10 % wt. loading, avoiding the use of further impregnation steps. In addition, the incorporation of metal precursors in the lignin solution enhances the development of mesoporosity in the resulting carbon fibers, a desirable feature for increasing mass transfer rate when used as electrocatalyst, without compromising their electrical conductivity. The electrochemical characterization has confirmed that these carbon cloths are promising ORR catalysts that could be useful for the reducing the amount of noble metals in the electrodes or for allowing the use of non-noble metals as catalysts.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO/FEDER CTQ2015-68654-R MINECO/FEDER CTQ2015-66080-R MINECO PTA2015-11464-

ASIGNACIÓN EFICIENTE DE CAPITAL EN LA BOLSA MEXICANA DE VALORES: UN ANÁLISIS COMPARATIVO ENTRE LAS METODOLOGÍAS DELTA NORMAL Y MÉTODO DE SIMULACIONES MONTE CARLO PARA ESTIMAR EL VALOR EN RIESGO

Este trabajo se centra principalmente en medir la máxima pérdida esperada en un intervalo de tiempo y un nivel de confianza dado de un portafolio diversificado (VaR). pág. 3 Concluyendo así que, aquel individuo que encuentre un gusto e interés por las inversiones debe contar con una visión más amplia de lo que implica el factor riesgo para el incremento de su capital y de esta manera ampliar su panorama al momento de invertir en cualquier mercado financiero. El presente trabajo está integrado por 4 capítulos: En el primer capítulo se explicará el Sistema Financiero Mexicano y su funcionamiento, así como los organismos y sectores que lo integran. Además detallaremos de manera más profunda los mercados financieros, su clasificación y los activos que se negocian en ellos. Es en el segundo capítulo donde se describe más a detalle el funcionamiento del Mercado de Capitales de México y las leyes que lo regulan, a su vez, se define y explica el concepto de “acción” y sus diferentes tipos de clasificación. Adicionalmente, se explica a manera breve el funcionamiento del SENTRA-Capitales y, finalmente en este apartado se revisa la conformación de dos de los índices de la Bolsa Mexicana de Valores: IPC e INMEX. Esto a manera introductoria para la selección de la muestra como objeto de la presente tesis. En el tercer capítulo se revisa la conceptualización del riesgo y se enfatiza su importancia dentro de la selección de portafolio de inversión. Por tanto, se revisa cada tipo de riesgo en base a la CUB (Circular Única de Bancos) y su relación con el Acuerdo de Basilea II. Por otra parte, se expone la Teoría de Selección de Carteras mediante el modelo de Harry Markowitz para que en el capítulo cuatro se pueda llevar a cabo la conformación de un portafolio de inversión. Por último, en el cuarto capítulo se describirá el concepto del Valor en Riesgo, las variables que intervienen en él y la metodología que se utiliza para su cálculo. También se plantará nuestro caso práctico en donde se creará un portafolio de inversión con acciones cotizantes en la Bolsa Mexicana de Valores y que forman parte del INMEX, las pág. 4 cuales minimicen el riesgo. Se procederá obtener el VaR por ambos métodos de estudio y a comparar sus resultados. Por último y no menos importante, una vez obtenidos los datos cuantitativos del caso práctico se obtendrán las conclusiones del presente trabajo

Efecto del H3PO4 en la preparación de fibras de carbono a partir de lignina. Mejoras en el proceso de estabilización y propiedades finales

El presente trabajo propone un nuevo método de preparación de fibras de carbono mediante electrohilado de mezclas de lignina/H3PO4, en el que se obtienen resultados que aceleran el proceso de preparación de estos materiales así como sus propiedades físico-químicas en una sola etapa de preparación. Será objeto de estudio la temperatura, tiempo y velocidad de calentamiento en la etapa de estabilización así como la atmósfera (inerte u oxidante) de estabilización y carbonización.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Efectos del origen de la semilla en la regeneración post incendio en pinus pinaster. el caso de la Dehesa de Solanillos (Guadalajara)

El mal estado selvícola con que llegaron las masas forestales a fines del siglo XIX promovió una gestión centrada en incrementar densidades y en recuperar calveros. La carencia de medios de los Distritos Forestales permite asumir una introducción de semilla/planta de otras procedencias de P. pinaster, como se ha constatado en este trabajo en los pinares de la “Dehesa Común de Solanillos”, monte con un Proyecto de Ordenación que data de 1905 y de 6 Revisiones que recogen las actuaciones hasta 1983 y, en especial, las siembras y repoblaciones efectuadas desde la redacción del proyecto inicial. Tras un incendio las zonas repobladas no mostraron la regeneración que cabría esperar debido a la ausencia del carácter serótino de las piñas que sí tienen las piñas de la procedencia local. Se ha constatado que la regeneración natural en aquellos terrenos poblados antes del incendio con masa natural poseen densidades suficientes para asegurar la persistencia del pinar

Adsorción de contaminantes farmacéuticos sobre monolitos de carbón activo

La eliminación de contaminantes emergentes de origen farmacéutico mediante adsorción está adquiriendo una gran importancia debido a que muchos de ellos poseen una alta estabilidad química y térmica, y son biológicamente activos. Muchos de estos contaminantes han sido detectados en aguas superficiales a niveles cercanos a los 100g/L [1]. Debido a la baja eficiencia de los sistemas de depuración de aguas residuales sobre la eliminación de estos contaminantes, es necesario el uso de sistemas avanzados, como la adsorción, para conseguir eliminar estos contaminantes. En este trabajo se muestran los resultados obtenidos al realizar estudios termodinámicos y cinéticos de la adsorción de productos farmacéuticos a bajas concentraciones (carbamazepina y paracetamol <20 mg/L) sobre distintos materiales monolíticos obtenidos mediante activación química con H3PO4.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech