Ce-Co and La-Co mixed oxides were synthesised by two different methods: exotemplating and evaporation. The obtained catalysts were evaluated for volatile organic compounds (VOCs) abatement, using toluene as model molecule. The materials were characterised by N 2 adsorption at -196 ºC, X-ray diffraction (XRD), scanning © 2014. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ electron microscopy (SEM), H 2 temperature programmed reduction (H 2 -TPR) and NH 3 temperature programmed desorption (NH 3 -TPD) in order to reveal the structure-activity relationship. The results obtained showed the superiority of mixed oxides compared to single oxides in toluene oxidation. Ce-Co mixed oxides were more active than La-Co samples. For Ce-Co materials, the exotemplating method produced catalysts which were more active than those prepared by the evaporation procedure. The former showed the best catalytic performances, with full conversion of toluene into CO 2 at about 250 o C.Temperatures higher than 320 o C were required with single oxides. Characterization studies revealed strong interactions between Ce (or La) and Co, leading to a fine dispersion of oxide phases in binary systems. As a result, both the surface area and reducibility of the catalysts increase, which can be accounted for the higher performance of the mixed oxides. Furthermore, NH 3 -TPD studies showed a linear relationship between acidity and VOC oxidation activity. In fact, a high concentration of weak acid sites is required for high toluene oxidation activity. The results can be explained in terms of a Mars-van Krevelen type of mechanism, involving the adsorption of toluene and its subsequent oxidation by lattice and/or surface oxygen.

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The influence of ball-milling in the texture and surface chemistry of multi-walled carbon nanotubes (MWCNT) was studied in this work. Treatment times up to 360 min at constant frequency (15 vibrations/s) and frequencies from 10 to 20 vibrations/s during 30 min were used for the preparation of the modified samples. These were characterized by nitrogen adsorption at-196 ºC, temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The milled samples were used as catalysts for the ozonation of oxalic acid. The surface area of the MWCNT increases, whereas the particle size decreases with the ball-milling time until 240 min at 15 vibrations/s. The functionalization of MWCNT surface is not achieved by ball-milling under the conditions used. The catalytic performance of the ball-milled samples for oxalic acid mineralization increased significantly when compared to the unmilled MWCNT. Therefore, ball-milling is an effective and simple method to increase the surface area of commercial carbon nanotubes without significant changes of their structural properties, and, consequently, this method allows increasing their catalytic performance in ozonation processes.

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The reduction of bromate to bromide was successfully catalyzed by mono and bimetallic catalysts based on ZSM5 zeolites. This reaction is important since the presence of bromate in water is potentially carcinogenic to humans. The catalysts were prepared by ion-exchange and incipient wetness methods with different metals (copper, palladium, rhodium and thorium) using ZSM5. Several analytical techniques (N 2 adsorption, TPR experiments, NH 3 -TPD, FTIR, XRD, SEM/EDX and TEM/EDX) were used to characterize the mono and bimetallic catalysts prepared by the two methods. The catalytic tests were carried out in a semi-batch reactor under hydrogen, working at room temperature and pressure. All catalysts prepared are undeniably effective in achieving the complete conversion of bromate into bromide. The most promising among the catalysts tested in this work are the palladium bimetallic catalysts.