Characterization of nanostructured allophane clays and their use as support of iron species in a heterogeneous electro-Fenton system.

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Electrooxidation of Chlorophenols Catalyzed by Nickel Octadecylphthalocyanine Adsorbed on Single-Walled Carbon Nanotubes

We described the synthesis of nickel octadecylphthalocyanine (NiPc(C10H21)8), followed by its adsorption on single-walled carbon nanotubes (SWCNT) to form SWCNT-NiPc(C10H21)8 conjugates. SWCNT-NiPc(C10H21)8 was used to modify a glassy carbon electrode (GCE) and for the electrooxidation of 4-chlorophenol and 2,4-dichlorophenol. The SWCNT and NiPc(C10H21)8 have a synergistic effect on each other in terms of improving electrocatalysis for the detection of chlorophenols. The stability of the electrode improved in the presence of NiPc(C10H21)8 or NiPc compared to the bare GCE. The presence of SWCNT improves the electrocatalytic behaviour of NiPc(C10H21)8 but not of unsubstituted NiPc. All modified electrodes showed improved stability towards the detection of 2,4-dichlorophenol. The best stability for 4-CP detection was observed in the presence of SWCNT for NiPc(C10H21)8

Migration of surface species on supports: a proof of their role on the synergism between CoSx or NiSx and MoS2 in HDS

Synergetic effects in hydrodesulfurization (HDS) have been investigated in operating conditions different from all those mentioned in literature yet. A synergism is observed between Co(x)/gamma-Al2O3 or Ni(x)/gamma-Al2O3, and Mo(y)/gamma-Al2O3 beds separated by a 5 mm, of gamma-Al2O3 or SiO2 bed. The results were obtained in conditions very close to those of industrial processes, namely using a high-pressure continuous-flow-reactor and gas-oil as feed, in contrast to model feeds used in most similar experiments. Compared to the activity of the individual beds, a significant increase of HDS activity is observed at 325, 350 and 375 degreesC, in the case of Co and Ni. As the Co (Ni) containing beds are physically separated from each other, no mutual contamination susceptible to lead to the formation of Co-Mo-S or Ni-Mo-S is possible. Several other alternative explanations have been examined, but it seems that the logical conclusion is that spillover of hydrogen could explain the phenomenon. No synergetic effect was detected using SiC as separator. The effects of changes in the cobalt or nickel (x), and molybdenum (y) contents and of the reaction temperature over the synergetic effect are also described and discussed. The effect of a diffusion of spillover species (probably hydrogen H-so) over a 5 mm distance is so conspicuous that it seems difficult to rule out an important flow of H-so and thus a much stronger effect in real CoMo and NiMo catalysts where the sulfided elements are at nanometer distances from each other. This makes even reasonable the hypothesis that hydrogen spillover could actually play an essential role in the HDS reaction over molybdenum-containing catalysts. (C) 2004 Elsevier B.V. All rights reserved

Electrooxidation of 2-chlorophenol and 2,4,6-chlorophenol on glassy carbon electrodes modified with graphite-zeolite mixtures

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