Structured catalysts were prepared, characterized and evaluated in NO 3 removal from drinking water. Different suspensions containing a previously optimized PdCu/5wt% ZrO 2-Al 2 O 3 powder catalyst (hereinafter PdCu/5ZA p) were prepared and deposited on cordierite monoliths by washcoating. The effect of suspension concentration, the particle size, the immersion number, the use of suspension stabilizer agent, and an alumina precoating on the coating adherence and catalytic performance were studied. All the prepared structured catalysts were active for the elimination of NO 3 and presented good selectivity to N 2 (> 93%) in synthetic water samples. The catalyst performance was related to the amount of deposited catalyst. The highest activity and the best coating adherence were obtained with the structured catalyst prepared by a single immersion in a 14 wt% concentration suspension, which was obtained from the powder catalyst milled for 10 h and stabilized with colloidal alumina. This catalyst also showed good activity when it was reused for four cycles and when it was evaluated with real water samples.
The removal of NO 3 − from water was performed and compared among four organo-montmorillonites (OMt) with quaternary amine surfactants of different chain lengths [octadecyl trimethyl-(ODTMA), hexadecyl trimethyl-(HDTMA), tetradecyl trimethyl-(TDTMA) and dodecyl trimethyl-ammonium (DDTMA)] and loadings [100%, 200%, 400% of the Mt cation exchange capacity (CEC)]. The maximum adsorption of NO 3 − was attained by the long chain length surfactants (64 and 100 mg NO 3 − ions per gram of OMt, for HDTMA and ODTMA, respectively) with initial loading of 400% with respect to the CEC of Mt. The short chain length surfactants (DDTMA and TDTMA) did not show adsorption of NO 3 − except for TDTMA 400 sample. The NO 3 − adsorption produced a slight expansion of the interlayer thickness of the OMt samples loaded with long-chain surfactants that was assigned to the entrance of NO 3 − by a synergic effect with these surfactants. The decrease of the negative zeta potential, found for OMt samples relative to that of Mt sample, was attributed to the surfactant chain length rather than to the actual surfactant loaded amounts, which allowed attaining positive zeta potential values for the OMt loaded with long-chain surfactants. The NO 3 − adsorption on OMt samples caused a slight decrease in the positive zeta potential values, reflecting the external surface coating by NO 3 −. For long-chain molecules, this behaviour also indicated the formation of greater interactions such as ion pairs between the positive polar group of the surfactant and NO 3 − ions.
The investigation and development of technologies to remediate water contaminated with NO 3 − are constantly increasing. An economically and potentially effective alternative is based on the catalytic hydrogenation of NO 3 − to N 2 . With this objective, bimetallic RhMo 6 catalysts based on Anderson-type heteropolyanion (RhMo 6 O 24 H 6 ) 3− were prepared and characteri3ed in order to obtain well-defined bimetallic catalyst. The catalysts were supported on Al 2 O 3 with different textural properties and on silica. The heteropolyanion-support interaction wasanalysed by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The differences obtained in activity and selectivity to the different products can be assigned to the different interaction between the RhMo 6 Anderson phase and the supports. The RhMo 6 /G, (G: γ-Al 2 O 3 ) system showed the best catalytic performance. This catalyst exhibited the lowest reduction temperature of Rh and Mo in the TPR assay and a Rh/Mo surface ratio similar to that of the original phase, as observed by XPS analysis. These studies allowed us to verify a synergic effect between Rh and Mo, through which Mo reducibility was promoted by the presence of the noble metal. The catalytic activity was favoured by the active sites generated from the Anderson phase. This fact was confirmed by comparing the activity of RhMo 6 /G with that corresponding to a conventional catalyst prepared through successive impregnation of both Rh (III) and Mo (VI) salts.
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