Esther Bailón-García

Tailoring activated carbons for the development of specific adsorbents of gasoline vapors

The specific adsorption of oxygenated and aliphatic gasoline components onto activated carbons (ACs) was studied under static and dynamic conditions. Ethanol and n-octane were selected as target molecules. A highly porous activated carbon (CA) was prepared by means of two processes: carbonization and chemical activation of olive stone residues. Different types of oxygenated groups, identified and quantified by TPD and XPS, were generated on the CA surface using an oxidation treatment with ammonium peroxydisulfate and then selectively removed by thermal treatments, as confirmed by TPD results. Chemical and porous transformations were carefully analyzed throughout these processes and related to their VOC removal performance. The analysis of the adsorption process under static conditions and the thermal desorption of VOCs enabled us to determine the total adsorption capacity and regeneration possibilities. Breakthrough curves obtained for the adsorption process carried out under dynamic conditions provided information about the mass transfer zone in each adsorption bed. While n-octane adsorption is mainly determined by the porosity of activated carbons, ethanol adsorption is related to their surface chemistry, and in particular is enhanced by the presence of carboxylic acid groups.

Carbon–TiO2 composites as high-performance supercapacitor electrodes: synergistic effect between carbon and metal oxide phases

A series of carbon xerogels doped with different percentages of TiO2 has been studied as a tentative means of preparing electrodes for supercapacitors. Carbon composites were obtained by an inverse emulsion method in n-heptane, and after carbonization at 900 °C the metal oxide phase was well dispersed in the carbon phase with a crystal size of less than 4 nm, and only an anatase phase was detected. An increase in the percentage of TiO2 produced a decrease in the hydrophobicity of the composite, which improved the wettability of the electrodes. XPS results showed that Ti3+ and Ti4+ were present on the surface of samples, and the presence of both oxidation states can improve the electron mobility in the inorganic phase. The obtained composite materials possessed specific surface areas that ranged from 423 to 539 m2 g−1 and very well developed micro- and mesoporosity with a total pore volume that ranged from 0.361 to 0.480 cm3 g−1. The mean size of supermicropores increased as the percentage of TiO2 increased, whereas practically no variation was found in the size of ultramicropores. Two-electrode symmetric supercapacitors based on the carbon xerogel–TiO2 composites exhibited high electrochemical performance, which was better than that of other similar materials in the literature, and displayed high capacitance (up to 137 F g−1 at 0.250 A g−1 for the composite containing 20% TiO2), high capacitance retention (66–80%) at 20 A g−1 and a high energy density of 20.15 W h kg−1 at a power density of 138.11 W kg−1 in the voltage range of 0 V to 1.1 V. A sample with a combination of low hydrophobicity and an adequate micro/mesopore network with an intermediate content of TiO2 exhibited the best performance for energy storage. A floating test showed the very good cyclability of the synthesized materials.

Effect of calcination temperature of a copper ferrite synthesized by a sol-gel method on its structural characteristics and performance as Fenton catalyst to remove gallic acid from water

A copper ferrite synthesized by a sol-gel combustion method was calcined at different temperatures up to 800°C, determining changes in its structural characteristics and magnetic measurements and studying its catalytic performance in gallic acid removal by Fenton reaction. The main objective was to study the effect of the calcination temperature of copper ferrite on its crystalline phase formation and transformation, activity and metal ion leaching. The cubic-to-tetragonal transformation of the spinel occurred via its reaction with the CuO phase, displacing Fe3+ ions in B (octahedral) sites out of the spinel structure by the following reaction: 2Fe3+B+3CuO→Fe2O3+3Cu2+B. The catalysts showed superparamagnetic or substantial superparamagnetic behaviour. At higher calcination temperatures, catalyst activity was lower, and Cu ion leaching was markedly decreased. There was no Fe ion leaching with any catalyst. The as-prepared catalyst showed better catalytic performance than a commercial copper ferrite. Leached Cu ions acted as homogeneous catalysts, and their contribution to the overall removal mechanism was examined. Cu2O present in the as-prepared catalysts made only a small contribution to their activity. Finally, the reutilization of various catalysts was studied by performing different catalytic cycles.

Fitting the experimental conditions and characteristics of Pt/C catalyst for the selective hydrogenation of citral

ABSTRACT A Pt catalyst supported on activated carbon was prepared and pretreated at different conditions. Both experimental conditions and catalyst characteristics were optimized. The influence of the textural properties of the support on the catalytic performance, based on the study of the internal and external diffusional limitations, is presented. The Pt-dispersion and its localization along the porosity of the support, strongly influences the activity and the product distribution. The production of valuable unsaturated alcohols is favored using catalysts with a Pt-particle size of around 8 nm working at a high hydrogen pressure and moderate temperatures. Secondary reactions are favored by increasing the temperature and the presence of active particles inside the mesopores of the support.