The use of Pd catalysts on carbon-based structured materials for the catalytic hydrogenation of bromates in different types of water

[EN] The aim of this work is to study the activity of new Pd catalysts, supported on two different nano structured carbon materials, for bromate catalytic hydrogenation. The influence of the support has been studied, obtaining the best results with a palladium catalyst supported on carbon nanofibers (CNF) grown in sintered metal fibers (SMF). The results have shown the importance of the catalyst support in order to minimize the mass-transfer limitations ensuring an efficient catalyst use. In this way the most active catalysts are those with a mesoporous structure containing high dispersed Pd nanoparticles. The activity of this catalyst for bromate reduction has been tested in different types of water, namely, distilled water, natural water and industrial wastewater. It has been shown that the catalyst activity depends on the water matrix and bromate reduction rate depends on the hydrogen partial pressure. The potential use of the catalyst has been studied in a continuous reactor. It has been observed that the catalyst is active without any important deactivation at least during 100 h of reaction, but is necessary to avoid salt precipitation and plugging problems.The authors thank the European Union (European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement no. 226347 Project) for financial support. A.E. Palomares also acknowledges the support from the Spanish Government through the project MAT2012-38567-C02-01.Palomares Gimeno, AE.; Franch Martí, C.; Yuranova, T.; Kiwi-Minsker, L.; Garcia Bordeje, JE.; Derrouiche, S. (2014). The use of Pd catalysts on carbon-based structured materials for the catalytic hydrogenation of bromates in different types of water. Applied Catalysis B: Environmental. 146:186-191. https://doi.org/10.1016/j.apcatb.2013.02.056S18619114

Structured fibrous carbon-based catalyst for continuous nitrate removal from natural water

[EN] Bimetallic (Pd–Cu, Pd–Sn) nanoparticles supported on structured fibrous carbons (activated carbon fibers and carbon nanofibers grown on sintered metal fibers) were tested in nitrate removal of natural polluted water by hydrogen (a batch and continuous mode). Dependence of the activity/selectivity on catalyst chemical composition, promoter nature and metal particle size was studied. Sn-modified Pd nanoparticles showed higher N2 selectivity as compared to Cu-modified ones. The structured (Pd–Sn) nanoparticles supported on carbon nanofibers grown on Inconel sintered metal fibers demonstrated the best catalytic performance in an open flow reactor, providing optimal hydrodynamics properties.This work was carried out with the financial support of the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 226347.Yuranova, T.; Franch Martí, C.; Palomares Gimeno, AE.; García-Bordejé, E.; Kiwi-Minsker, L. (2012). Structured fibrous carbon-based catalyst for continuous nitrate removal from natural water. Applied Catalysis B: Environmental. 123-124:221-228. https://doi.org/10.1016/j.apcatb.2012.04.007S221228123-12

Self-Cleaning cotton textiles surfaces modified by photoactive SiO2/TiO2 coating

The photocatalytic activity of TiO2–SiO2-coated cotton textiles was investigated through the self-cleaning of red wine stains. It was shown that a TiO2–SiO2 species could be produced at temperatures of 100 °C with acceptable photo-activity on non-heat resistant materials. The most suitable Ti-content of the coating was found to be 5.8% and for SiO2, the content was 3.9% (w/w). The discoloration of red wine led to CO2 evolution that was more efficient for TiO2–SiO2-coated cotton for samples than of TiO2-coated ones. The reasons for these results are discussed. The textile surface did not show any change after several consecutive light-induced discoloration cycles of a red wine stain. By high-resolution transmission electron microscopy (HRTEM), the TiO2–SiO2 layer thickness on the cotton fibers was detected to 20–30 nm. The TiO2 and SiO2 were both observed to have particle sizes between 4 and 8 nm. Further electron microscopy work coupled with energy dispersive spectroscopy (EDS) showed that the Ti-particles were always surrounded by amorphous SiO2 and never alone by themselves. Infrared spectroscopy revealed that no modification of the cotton could be detected after photo-discoloration processes with TiO2–SiO2, taking a wine stain as model compound. The mixed TiO2 and SiO2 colloids lead during the dip-coating and subsequent thermal treatment on cotton to an organized structure of highly dispersed TiO2 particles always surrounded by amorphous silica

Silylation and sulfonation of structured supported catalysts active in the decoloration of azo-dyes under visible light

Structured silica woven fabrics have been derivatized with functional groups able to anchor by exchange of Fe3+-ions and TiO2 showing a stable performance during the visible light induced decoloration of the Orange II azo-dye. The kinetics and efficiency of the decoloration mediated by the catalytic loaded silica fabrics with Fe3+-ions were seen to be much higher than found with homogeneous Fenton reagents (Fe3+/H2O2) with the equivalent Fe3+ content. The same was observed for derivatized membranes where TiO2 has been anchored as the active catalyst surface species. In the case of the silica Fe3+-ions loaded fabrics, the decoloration was studied as a function of the amount of H2O2 oxidant added in solution, the intensity of the applied visible light and the concentration of the initial Orange II. In the case of the silica-TiO2 fabrics the decoloration kinetics was observed to be a function of the O2 present in solution. In the case of the derivatized Fe3+ and TiO2 loaded silica fabrics, the decoloration process presented three common features: (a) the decoloration process was observed only in the presence of light pointing to a photo-induced process in both cases, (b) the decoloration was also observed to be truly catalytical following repetitive cycles for Orange II, and finally (c) the decoloration processes were limited by the mass transfer kinetics taking place at the surface of both derivatized fabric catalyst and proceeded with about the same kinetics in both cases. The numerical values for the diffusion distance of the radicals species OHradical dot and HO2radical dot as well as the decrease in the concentration of radicals away from the silica fabric during the photodegradation of Orange II is estimated by the Smoluchowski diffusion equation

Testing and performance of immobilized Fenton photoreactions via membranes, mats and modified copolymers

During the last 6 years our laboratory has developed Fenton immobilized catalysts for the partial or total destruction of toxic organic compounds and their mixtures. This paper reports on Fe-supported noncorrosive supported membranes and fabrics like: Nafion, Nafion-glass mats and polyethylene block copolymers. These novel supported catalysts have shown acceptable kinetic rates, resistance to the leaching of Fe3+ into the solution and no corrosion to the highly oxidative radicals generated in the solution during Fenton immobilized photo-assisted catalysis. Nafion-Fe membranes degrade Orange II under visible light only up to pH 4.8. In the case of nafion glass mats supported Fe3+-ions, the initial pH could be raised up to 8 or above. The pH decreased to about 4 during the photodegradation of Orange II due to the formation of intermediate carboxylic acids but the costly initial acidification process necessary in the case of homogeneous Fenton processes is avoided. Carboxylates and carboxylic acids were observed by IR spectroscopy on the surface of the supported catalysts towards the end of the photodegradation process as well as carboxylic acids detected by HPLC. The IR bands are found at 1523 and 1557 cm-1 in the case of the copolymer-Fe3+ corresponding to two types of iron-carboxylate species. The formation of carboxylates explains the drop of pH during the photodegradation to values between 3 and 4 corresponding to the pKa of the carboxylic functional group