Sistemas de platino soportado aplicados a hidrogenación y fotooxidación selectivas

En esta tesis se ha estudiado el proceso de reducción quimioselectiva de compuestos carbonílicos ¿,ß-insaturados. El estudio se ha realizado desde el punto de vista de la selectividad hacia el alcohol insaturado, producto de la reducción selectiva del grupo carbonilo. El estudio se ha centrado en los catalizadores de platino soportado que presentan una cierta selectividad hacia dicho alcohol. Para ello se han seguido dos pasos: 1)Optimización de la selectividad en el proceso de los catalizadores de platino soportado mediante el análisis de la influencia del soporte y de las variables de activación del catalizador (Tª de reducción). 2)Una vez optimizadas las variables relativas al catalizador, se ha abordado el estudio de las condiciones de reacción, como temperatura, presión inicial de hidrógeno, aditivos y disolvente. También se ha estudiado el proceso de fotooxidación selectiva de 2-propanol en fase gaseosa para evaluar la actividad fotocatalizadora de distintos sistemas heterogéneos basados en TiO2 y ZnO. La reacción se ha aplicado para evaluar el efecto de la incorporación de Pt a un óxido de titanio comercial (P25, de la casa Degussa) utilizado habitualmente como fotocatalizador de referencia y del ZnO. Del mismo modo se ha utilizado sistemas de TiO2 soportado sobre fosfatos naturales

Influence of Boron, Tungsten and Molybdenum Modifiers on Zirconia Based Pt Catalyst for Glycerol Valorization

The influence of boron, tungsten and molybdenum modifiers on zirconia-based Pt catalyst was studied for glycerol valorization. Zirconia modified supports were prepared by impregnation of ZrO2 with either boric, silicontungstic or phosphomolybdic acids to obtain supports with enhanced Brönsted acidic properties. The modified supports were subsequently impregnated with chloroplatinic acid to obtain Pt-based catalysts. Pt incorporation resulted in the increase in Lewis acidity of the solids, being more significant for the Pt//W/ZrO2 catalyst. Reduced Pt catalysts were tested for the liquid-phase glycerol hydrogenolysis, observing a synergistic effect between catalyst acid sites and metal function that proved to be crucial in glycerol hydrogenolysis. The Pt//W/ZrO2 catalyst was the most active catalyst in this reaction, being the only leading to 1,3-PDO (45% sel., 160 °C) while Pt//Mo/ZrO2 is the best option for 1,2-PDO (49% sel., 180 °C). Reusability studies carried out for Pt//W/ZrO2 showed that catalytic activity dropped after the first use, remaining constant for the second and subsequent ones. Selectivity to reaction products also changes during reuses. Therefore, the selectivity to 1,2 PDO increases in the first reuse in detriment to the selectivity to n-propanol whereas the selectivity to 1,3-PDO remains constant along the uses. This behavior could be associated to the lixiviation of W species and/or catalyst fouling during reaction runs

Hydrogen Photo-Production from Glycerol Using Nickel-Doped TiO2 Catalysts: Effect of Catalyst Pre-Treatment

In the present piece of research, hydrogen production via the photo-reforming of glycerol (a byproduct from biodiesel generation) is studied. Catalysts consisted of titania modified by Ni (0.5% by weight) obtained through deposition–precipitation or impregnation synthetic methods (labelled as Ni-0.5-DP and Ni-0.5-IMP, respectively). Reactions were performed both under UV and solar irradiation. Activity significantly improved in the presence of Ni, especially under solar irradiation. Moreover, pre-reduced solids exhibited higher catalytic activities than untreated solids, despite the “in-situ” reduction of nickel species and the elimination of surface chlorides under reaction conditions (as evidenced by XPS). It is possible that the catalyst pretreatment at 400 °C under hydrogen resulted in some strong metal–support interactions. In summary, the highest hydrogen production value (ca. 2600 micromole H2·g−1) was achieved with pre-reduced Ni-0.5-DP solid using UV light for an irradiation time of 6 h. This value represents a 15.7-fold increase as compared to Evonik P25

Olive Leaves as Biotemplates for Enhanced Solar-Light Harvesting by a Titania-Based Solid

Olive leaves (by-product from olive oil production in olive mills) were used as biotemplates to synthesize a titania-based artificial olive leaf (AOL). Scanning electron microscopy (SEM) images of AOL showed the successful replication of trichomes and internal structure channels present in olive leaves. The BET surface area of AOL was 52 m2·g−1. X-ray diffraction (XRD) and Raman spectra revealed that the resulting solid was in the predominantly-anatase crystalline form (7.5 nm average particle size). Moreover, the synthesis led to a red-shift in light absorption as compared to reference anatase (gap energies of 2.98 and 3.2 eV, respectively). The presence of surface defects (as evidenced by X-ray photoelectron spectroscopy, XPS, and electron paramagnetic resonance spectroscopy, EPR) and doping elements (e.g., 1% nitrogen, observed by elemental analysis and XPS) could account for that. AOL was preliminarily tested as a catalyst for hydrogen production through glycerol photoreforming and exhibited an activity 64% higher than reference material Evonik P25 under solar irradiation and 144% greater under ultraviolet radiation, (under voltage) UV

Dificultades interpersonales en la adolescencia : ¿Factor de riesgo de fobia social?

The main aim of this study was to analyse the relationship between interpersonal difficulties in adolescence, on the one hand, with social phobia (both generalized and non-generalized), and, on the other hand, with personality variables (intraversion and neuroticism). A sample of 538 schoolchildren between the ages of 12 to 18 were recruited. They then filled in the following set of self-reports: the Questionnaire about Interpersonal Difficulties for Adolescents, the Social Phobia and Anxiety Inventory, the Personal Report of Confidence as Speaker (shortened 12- item version), and the Eysenck Personality Questionnaire. Adolescents with generalized social phobia, with fear of public speaking, introverted, and emotionally instable reported more interpersonal difficulties than adolescents without generalized social phobia, without fear of public speaking, extraverted, and emotionally stable (p<0.001). The prevalence of generalized social phobia was 8.18% and was more frequent among females than among males, with a proportion of 2:1, reaching a peak in mid-adolescence (14-15 years old).El principal objetivo de este estudio fue analizar la relación de las dificultades interpersonales en la adolescencia, por un lado, con la fobia social (generalizada y no generalizada) y, por otro, con variables de personalidad (introversión y neuroticismo). Se reclutó una muestra de 538 escolares, de 12 a 18 años, que cumplimentaron la siguiente batería de autoinformes: Cuestionario de Evaluación de Dificultades Interpersonales en la Adolescencia, Inventario de Ansiedad y Fobia Social, Cuestionario de Confianza para Hablar en Público (versión abreviada de 12 Ítems), y Cuestionario de Personalidad de Eysenck. Los adolescentes con fobia social generalizada, miedo a hablar en público, introvertidos e inestables emocionales, informaron más dificultades interpersonales que los adolescentes sin fobia social generalizada, sin miedo a hablar en público, extravertidos y estables emocionales [p 0,001). La prevalencia de fobia social generalizada fue 8,18%, siendo más frecuente en el género femenino que en el masculino en proporción 2:1, y alcanzando un pico en la adolescencia media (14- 15 años)

Bio-Templating: An Emerging Synthetic Technique for Catalysts. A Review

In the last few years, researchers have focused their attention on the synthesis of new catalyst structures based on or inspired by nature. Biotemplating involves the transfer of biological structures to inorganic materials through artificial mineralization processes. This approach offers the main advantage of allowing morphological control of the product, as a template with the desired morphology can be pre-determined, as long as it is found in nature. This way, natural evolution through millions of years can provide us with new synthetic pathways to develop some novel functional materials with advantageous properties, such as sophistication, miniaturization, hybridization, hierarchical organization, resistance, and adaptability to the required need. The field of application of these materials is very wide, covering nanomedicine, energy capture and storage, sensors, biocompatible materials, adsorbents, and catalysis. In the latter case, bio-inspired materials can be applied as catalysts requiring different types of active sites (i.e., redox, acidic, basic sites, or a combination of them) to a wide range of processes, including conventional thermal catalysis, photocatalysis, or electrocatalysis, among others. This review aims to cover current experimental studies in the field of biotemplating materials synthesis and their characterization, focusing on their application in heterogeneous catalysis