Microcalorimetric and IR spectroscopic studies of CO adsorption on molybdenum nitride catalysts

The adsorption of CO on both nitrided and reduced passivated Mo(2)N catalysts in either alumina supported or unsupported forms was studied by adsorption microcalorimetry and infrared (IR) spectroscopy. The CO is adsorbed on nitrided Mo(2)N catalysts on three different surface sites: 4-fold vacancies, Mo(delta+) ( 0 < delta < 2) and N sites, with differential heats of CO adsorption decreasing in the same order. The presence of the alumina-support affects the energetic distribution of the adsorption sites on the nitrided Mo(2)N, i.e. weakens the CO adsorption strength on the different sites and changes the fraction of sites adsorbing CO in a specific form, revealing that the alumina supported Mo(2)N phase shows lower electron density than pure Mo(2)N. On reduced passivated Mo(2)N catalysts the CO was found to adsorb mainly on Mo(4+) sites, although some slightly different surface Mo(delta+) d (0 < delta < 2) sites are also detected. The nature, density and distribution of surface sites of reduced passivated Mo(2)N/gAl(2)O(3) were similar to those on reduced MoO(3)/gamma-Al(2)O(3)

Carbon nanotubes and nanofibers based catalysts for bioethanol activation

Trabajo presentado en la 5th International Conference on Carbon for Energy Storage/Conversion and Environment Protection, celebrada en Mülheim an der Ruhr (Alemania) del 23 al 26 de septiembre de 2013.[Introduction] Bioethanol obtained from agriculture products (corn, sugarcane, etc) is largely used as additive in transportation fuels. However, the upgrading of ethanol to produce valuable chemicals, either for application as direct fuel or as chemical intermediates (i.e. butanol, acetone) is an interesting subject of research. The more feasible transformations of ethanol by heterogeneous catalysis are those yielding ethylene or acetaldehyde. In the first case ethanol is transformed by dehydration, usually over acid surface sites, while acetaldehyde is obtained by dehydrogenation over basic surface sites. A part from these aspects bioethanol contains significant amounts of water that can hinder or deactivate the catalysts during their transformation reactions. The surface hydrophobicity of carbons makes these materials very promising for their application as catalysts in bioethanol transformation.[Experimental] In this communication we present the catalytic properties, mainly due to basic surface sites, of 4 carbon materials. These are: two commercial nanofiber from Pyrograph Products Inc (with different degree of surface graphitization) and two multiwall carbon nanotubes, one of them provided by Nanocyl and the other lab prepared following the procedure described in [1]. These four carbon materials were also treated with fuming sulfuric acid (20% free SO3) at 80 ºC, in order to incorporate sulphonic groups. The sulphonated materials were tested in dehydration of bioethanol applying their acidic properties. The tests of catalytic behavior where conduced in a continuous flow reactor feeding a mixture of ethanol (either pure or containing water at 10%) in an inert gas carrier He. The analysis of the reaction products were performed using a gas chromatograph apparatus. The samples were characterized mainly by temperature programmed decomposition (TPD) and by X-ray photoelectron spectroscopy (XPS).[Results and discussion] In Table 1 are presented some catalytic results. It is seen that the specific activity for ethanol dehydrogenation increases with the surface graphitization degree of materials (CNF-HHT vs CNF-PS and MWCNT-2 vs MWCNT-1). This suggests that basic sites can be related with graphitic structures. Concerning the dehydration reaction over sulphonated samples can be indicated that catalytic activities are related with the area of SO2 evolved during TPD, as well as with the amount of S detected in XPS analysis. Finally it should be noticed that the thermal stabilities of these samples is very limited.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