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

Effect of pH on the Nitrite Hydrogenation Mechanism over Pd/Al2O3 and Pt/Al2O3: Details Obtained with ATR-IR Spectroscopy

It is well-known that activity and selectivity to N2 during nitrite hydrogenation over noble metal catalysts in water depend on the pH of the solution, but mechanistic understanding is lacking. Attenuated total reflection infrared (ATR-IR) spectroscopy is an ideal tool to perform detailed studies on catalytic surfaces in water. In this paper, the influence of pH was studied on adsorption and subsequent hydrogenation of nitrite in water between pH 5 and 9 over Pd/Al2O3 and Pt/Al2O3, using ATR-IR spectroscopy. On both catalysts, pH clearly influenced the surface coverage and reaction rates of intermediates. For Pt/Al2O3, lowering the pH induced the increasing surface coverage of key reaction intermediates like NOsteps1620 cm−1 and “HNO”(ads)1540 cm−1, as well as increased hydrogenation rates, explaining the higher TOF at lower pH as reported in the literature. For Pd/Al2O3, the effect of pH on selectivity is controlled by the rate constants of the formation and hydrogenation of the most stable reaction intermediates to N2 (NO(ads)1720 cm−1) and NH4+ (NH2(ads)1510 cm−1)

Removal of the x-ray contrast media diatrizoate by electrochemical reduction and oxidation

Due to their resistance to biological wastewater treatment, iodinated X-ray contrast media (ICM) have been detected in municipal wastewater effluents at relatively high concentrations (i.e., up to 100 μg L–1), with hospitals serving as their main source. To provide a new approach for reducing the concentrations of ICMs in wastewater, electrochemical reduction at three-dimensional graphite felt and graphite felt doped with palladium nanoparticles was examined as a means for deiodination of the common ICM diatrizoate. The presence of palladium nanoparticles significantly enhanced the removal of diatrizoate and enabled its complete deiodination to 3,5-diacetamidobenzoic acid. When the system was employed in the treatment of hospital wastewater, diatrizoate was reduced, but the extent of electrochemical reduction decreased as a result of competing reactions with solutes in the matrix. Following electrochemical reduction of diatrizoate to 3,5-diacetamidobenzoic acid, electrochemical oxidation with boron-doped diamond (BDD) anodes was employed. 3,5-Diacetamidobenzoic acid disappeared from solution at a rate that was similar to that of diatrizoate, but it was more readily mineralized than the parent compound. When electrochemical reduction and oxidation were coupled in a three-compartment reactor operated in a continuous mode, complete deiodination of diatrizoate was achieved at an applied cathode potential of −1.7 V vs SHE, with the released iodide ions electrodialyzed in a central compartment with 80% efficiency. The resulting BDD anode potential (i.e., +3.4–3.5 V vs SHE) enabled efficient oxidation of the products of the reductive step. The presence of other anions (e.g., chloride) was likely responsible for a decrease in I– separation efficiency when hospital wastewater was treated. Reductive deiodination combined with oxidative degradation provides benefits over oxidative treatment methods because it does not produce stable iodinated intermediates. Nevertheless, the process must be further optimized for the conditions encountered in hospital wastewater to improve the separation efficiency of halide ions prior to the electrooxidation step