Catalizadores de Pd soportados en oxido de grafito y en sus derivados exfoliados aplicados en la hidrogenación de 1,3-butadieno

Trabajo presentado en el XXIV Congreso Iberoamericano de Catálisis, celebrado en Medellín (Colombia) del 14 al 19 de septiembre de 2014.Se prepararon dos series de catalizadores de Pd soportados sobre oxido grafitico y sus derivados exfoliados, empleando el método de intercambio y el método de impregnación, y se estudiaron en la reacción de hidrogenación del 1,3-butadieno. En la primera serie se redujeron las muestras a distintas temperaturas y sin exfoliar el oxido grafitico, y se observo un aumento en la actividad y selectividad hacia los productos deseados con la temperatura de reducción. En la segunda serie estudio la influencia de la etapa en la que tenía lugar la exfoliación del soporte sobre el comportamiento catalítico del Pd. Se consiguieron resultados optimizados de selectividad hacia butenos (98%) y en particular hacia el 1-buteno.Se agradece la financiación de este trabajo a cargo de los proyectos CTQ 2011-29272-C04-01 y 03 y del 2011/PUNED/0001.Peer Reviewe

Role of exposed surfaces on zinc oxide nanostructures in the catalytic ethanol transformation

For a series of nanometric ZnO materials, the relationship between their morphological and surface functionalities and their catalytic properties in the selective decomposition of ethanol to yield acetaldehyde was explored. Six ZnO solids were prepared by a microemulsion-precipitation method and the thermal decomposition of different precursors and compared with a commercial sample. All these materials were characterized intensively by XRD and SEM to obtain their morphological specificities. Additionally, surface area determinations and IR spectroscopy were used to detect differences in the surface properties. The density of acid surface sites was determined quantitatively using an isopropanol dehydration test. Based on these characterization studies and on the results of the catalytic tests, it has been established that ZnO basal surfaces seem to be responsible for the production of ethylene as a minor product as well as for secondary reactions that yield acetyl acetate. Furthermore, one specific type of exposed hydroxyl groups appears to govern the surface catalytic properties.The financial support of the Spanish government by Projects CTQ2011‐29272‐C04‐01 and CTQ2011‐29272‐C04‐03 is recognized. M.V.M. appreciates the financial support of UNED by a predoctoral grant.Peer Reviewe

Importance of basic sites on ZnO surfaces for bioethanol valorization

Trabajo presentado en el International Congress on Green Chemistry and Sustainable Engineering, celebrado en Barcelona (España), del 29 al 31 de julio de 2014.One of the major products of biomass conversion is ethanol, which can be the raw material to manufacture a number of chemical products. For example, dehydrogenation of ethanol using basic catalysts leads to acetaldehyde, which has been categorized as one of the promising bioethanol derivates from a sustainable perspective. One of the materials that catalyzes this reaction is ZnO, which crystallizes in a wurtzite-type structure, where the polar faces, (0001) and ( ), are located perpendicular to the c-axis while the nonpolar ones), are parallel to it. The polar/nonpolar facet ratio is often argued to be a key aspect in the photochemical catalytic activity. However, unlike in photocatalysis, in this reaction very little is known concerning the direct relation between ZnO morphology (i.e. polar/nonpolar facet ratio) and its catalytic performances. In this communication we present the catalytic properties of six polycrystalline ZnO samples used in the decomposition of ethanol.Peer Reviewe

Selective 1,3-butadiene hydrogenation by gold nanoparticles deposited & precipitated onto nano-carbon materials

Graphene oxide and multiwall carbon nanotubes (CNTs) were chemically modified by treatment with urea and subsequent annealing at different temperatures. These materials were used as supports for gold nanoparticles and the resulting samples have been applied as catalysts in the 1,3-butadiene partial hydrogenation reaction. The supports and catalysts were exhaustively characterized. It was shown that urea treatments modified the graphene surfaces and the morphology of CNTs, in both cases with incorporation of significant amounts of different nitrogen surface groups. The presence of these groups on few layered graphene or on CNT surfaces modifies the gold precipitation–deposition process during catalyst preparation, giving place to different amounts of incorporated gold on the various supports. The obtained catalytic results suggested that the partial hydrogenation requires limited availability of hydrogen, and for this the migration through adsorbed species between the metal and support to initiate the hydrogenation, probably by a spillover mechanism, seems to be a required step. In general intramolecular selectivity is structure-sensitive meanwhile catalytic activity is not structure-sensitive, as evidenced when the gold nanoparticle sizes are decreased.E C gratefully acknowledges nancial support from the Spanish Ministry of Science and Technology and from the UNED postdoc programme. This work was supported by the Spanish Government (project CTQ 2011-29272-C04-01and 03).Peer Reviewe

Desde el ácido grafítico al óxido de grafeno: propiedades y aplicaciones derivadas de su química superficial

Trabajo presentado en la XXXIV Reunión Bienal de la Real Sociedad Española de Química, celebrada en Santander (España) del 15 al 18 de septiembre de 2013.La concesión del premio Nobel de Física en 2010 a los investigadores A. Geim y K. Novoselov por sus trabajos sobre el grafeno, ha despertado un enorme interés en los materiales laminares derivados del grafito. El número de publicaciones científicas realizadas sobre óxido gráfitico ha pasado desde una media de menos de 20, hasta 2004, a más de 130 en 2012; mientras que los artículos que contienen el término óxido de grafeno, han sido más de 3000 en 2012 (y hasta 2007 no se usaba este término). De hecho lo que hace pocos años llamábamos ácido u óxido grafítico ha pasado a designarse como óxido de grafeno. Los campos donde son aplicados los óxidos de grafito o de grafeno (OGs) también han aumentado exponencialmente, pasando de ser aplicados como adsorbentes de contaminantes de aguas (grafitos expandidos) a ser mencionados como refuerzo de polímeros, como material para producir baterías de Li, como componentes de sensores de gases, para fabricar semiconductores o ultracondensadores o electrodos, etc. Aparte estarían las aplicaciones catalíticas de las que cabe destacar las fotocatalíticas (con TiO2). Cabe resaltar que los OGs son materiales muy versátiles, y que permiten combinarse con otros sólidos para conseguir muy diversos ¿materiales compuestos¿. Además los OGs pueden ser la base para producir grafeno. Igualmente las propiedades de superficie de los OGs son interesantes ya que permiten anclar en sus superficies compuestos moleculares que, por ejemplo, pueden tener propiedades catalíticas. En esta comunicación se van a presentar algunos resultados recientes de nuestro grupo de investigación, en los que tras inmovilizar el complejo Ru-BINAP en los OGs lo aplicamos como catalizador enantioselectivo en la hidrogenación de metilacetoacetato; o cuando comprobamos una mayor estabilidad como catalizador en hidrogenación de cinamaldehido del complejo Ru(PPh3)3Cl2 enlazado covalentemente sobre OGs funcionalizados usando [3-(2-Aminoetilamino)propil]trimetoxisilano. Asimismo hemos introducido funciones básicas, al realizar el proceso de exfoliación de OGs en atmósfera de amoniaco, y las aplicamos como catalizadores en la deshidrogenación de bioetanol.Peer Reviewe

High nitrogen doped graphenes and their applicability as basic catalysts

N-doped and un-doped graphene samples were synthesized starting from natural graphite of different particle sizes (10, 100 and 200 mesh) by oxidation and further thermal treatment under ammonia and inert atmospheres, respectively. Samples were thoroughly characterized by TEM, XRD, Raman and XPS. The nature and quantity of nitrogen species introduced were dependent on starting materials, reduction atmosphere (NH3 or inert) and temperature. All samples were employed as basic catalysts in the dehydrogenation reaction of ethanol. Acetaldehyde was the main product obtained owing to the basicity induced by the presence of N atoms in the graphene layers. Conversion increased with higher N at.% and lower number of stacked graphene sheets. Catalysts with highest ratio between both factors gave highest conversion values.Authors acknowledge financial support from the projects CTQ 2011-29272-C04-01 and 03 and project 2011/PUNED/0001.Peer Reviewe

High nitrogen doped graphenes and their applicability as basic catalysts

Trabajo presentado en la International Conference on Diamond and Carbon Materials, celebrada en Riva del Garda (Italia) del 2 al 5 de septiembre de 2013.Great emphasis has been dedicated to the electronic properties of graphene. These properties can be modified by introducing heteroatoms such as boron or nitrogen in the carbon structure during or after graphene synthesis process. In this work we study the nitrogen doping effect of graphene on the catalytic dehydrogenation reaction of ethanol. Nitrogen atoms were introduced via insitu reduction of graphite oxides of various grain sizes (10, 100 and 200 mesh) which had been previously prepared following a modification of the brodie method. The obtained GO were treated under an inert atmosphere (50 mL/min N2) and in a reaction mixture of NH3 (10 mL/min), N2 (50 mL/min) and H2 (6 mL/min). All samples were heated until 773 K although one of them was also heated at 1173 K. The resulting materials were characterized by Raman, XPS, XRD, etc. XRD results proved both successful graphite oxidation (interlayer spacing increases from 0.35 to 0.67 nm) and GO reduction (002 reflection peak disapears in all cases but for GO10 sample which partially recovers its graphitic nature). A Raman spectrum of one of the original graphite (G100) and its corresponding reduced GO (in inert atmosphere and in NH3) is depicted in Fig. 1. The parent graphite with strong G band and very small D gave an intensity ratio ID/IG of about 0.04. This is quite different for the reduced GO and at the same time dependent on the reduction atmosphere. Higher ID/IG ratio was observed for the nitrogen doped sample owing to the structure disorder caused by the presence of N atoms. XPS gave insights on the amount and type of nitrogen incorporated after the treatment which was dependent on graphite particle size and treatment temperature (Table 1). These characteristics are in agreement with the behaviour of samples in the dehydrogenation reaction of ethanol.Peer Reviewe

Bioethanol transformations over active surface sites generated on carbon nanotubes or carbon nanofibers materials

© Almohalla et al.; Licensee Bentham OpenCatalytic bioethanol transformations over carbon nanomaterials (nanofibers and nanotubes) have been evaluated at atmospheric pressure and in the temperature range of 473-773 K. The pristine carbon materials were compared with these samples after surface modification by introducing sulfonic groups. The specific activity for ethanol dehydrogenation, yielding acetaldehyde, increases with the surface graphitization degree for these materials. This suggests that some basic sites can be related with specific surface graphitic structures or with the conjugated basic sites produced after removing acidic oxygen surface groups. Concerning the dehydration reaction over sulfonated samples, it is observed that catalytic activities are related with the amount of incorporated sulfur species, as detected by the evolution of SO2 in the Temperature programmed Desorption (TPD) as well as by the analysis of sulfur by X-Ray Photoelectron Spectroscopy (XPS).The financial support of the Spanish government by Projects CTQ2011-29272-C04-01 and 03 is recognized.Peer Reviewe