RESUMEN
The catalytic reduction of nitrites over Pt-In catalysts supported on activated carbon has been studied in a semi-batch reactor, at room temperature and atmospheric pressure, and using hydrogen as the reducing agent. The influence of the indium content on the activity and selectivity was evaluated. Monometallic Pt catalysts are very active for nitrite reduction, but the addition of up to 1 wt% of indium significantly increases the nitrogen selectivity from 0 to 96%. The decrease in the accessible noble metal surface area reduces the amount of hydrogen available at the catalyst surface, this favoring the combination of nitrogen-containing intermediate molecules to promote the formation of N2 instead of being deeply hydrogenated into NH4+. Several activated carbon-supported Pt-In catalysts, activated under different calcination and reduction temperatures, have been also evaluated in nitrite reduction. The catalyst calcined and reduced at 400°C showed the best performance considering both the activity and the selectivity to nitrogen. This enhanced selectivity is ascribed to the formation of Pt-In alloy. The electronic properties of Pt change upon alloy formation, as it is demonstrated by XPS.
RESUMEN
Materials able to produce the reduction of nitrate from water without the need of a metal catalyst and with avoiding the use of gaseous hydrogen have been developed by combining the synergistic properties of titania and two conducting polymers. Polymerization of aniline and pyrrol on titanium dioxide in the presence of two different oxidants/dopants (iron trichloride or potassium persulfate) has been evaluated. The resulting hybrid materials have good thermal stability imparted by the titania counterpart, and a considerable conductivity provided by the conducting polymers. The capability of the hybrid materials of reducing aqueous nitrate has been assessed and compared to the catalytic hydrogenation of nitrate using a platinum catalyst supported on these hybrid synthesized materials. The mechanism of nitrate abatement implies adsorption of nitrate on the polymer by ion exchange with the dopant anion, followed by the reduction of nitrate. The electron transfer from titania to the conducting polymer in the hybrid material favors the reductive ability of the polymer, in such a way that nitrate is selectively reduced with a very low production of undesirable side products. The obtained results show that the activity and selectivity of the catalytic reduction of nitrate with dihydrogen in the presence of a platinum catalyst supported on the hybrid materials are considerably lower than those of the metal-free nanocomposites.
RESUMEN
We report a facile and general approach for preparing ultrafine ruthenium nanocatalysts by using a plasma-assisted synthesis at <100 °C. The resulting Ru nanoparticles are monodispersed (typical size 2â nm) and remain that way upon loading onto carbon and TiO2 supports. This gives robust catalysts with excellent activities in both organosilane oxidation and the oxygen evolution reaction.
RESUMEN
Three different conducting polymers, polythiophene (PT), polypirrol (PPY) and polyaniline (PANI) have been synthesized via oxidative chemical polymerization in aqueous media, in such a way that the synthesis protocol did not involve any toxic solvents. They have been tested in the abatement of nitrates from an aqueous solution without the need of any metal catalyst. The N-containing polymers (PANI and PPy) were able to remove nitrates to a level that accomplishes the European legislation requirements; however, the nature of each polymer greatly influenced the process mechanism. Whereas ion exchange between Cl- and SO42- counter-ions in the polymer and NO3- from water is the main responsible for the effective nitrate removal in PANI, as assessed by FTIR and XPS analyses, the nitrate removal mechanism on PPy is based in an electron transfer from the polymer to nitrate through N sites located in the pyrrolic ring. On the other hand, PT was not able to exchange nitrate unless it was synthesized with FeCl3 as oxidant/dopant and an anionic surfactant (sodium dodecyl sulfate -SDS-) is used. In that case, the electrostatic attraction between sulfate (OSO3-) groups from the surfactant and Fe3+ ions from FeCl3 produced the anchoring of Cl- to the oxidized PT growing chain, this favoring ion exchange with nitrate in the aqueous solution, followed by a redox process.
