Desarrollo de catalizadores a partir de metales recuperados de pilas

Se recuperaron Zn y Mn provenientes de pilas alcalinas por  lixiviación en medio ácido, tratándose la solución con NaOH o con KMnO4 obteniéndose dos óxidos ZnMnOx y MnOx, respectivamente, siendo  una porción del MnOx obtenido impregnado con una solución de Zn2+ proveniente de la solución lixiviada. Los sólidos fueron caracterizados y fue  analizada su actividad catalítica en la oxidación total  de tolueno y etanol

Synthesis and catalytic activity of manganese dioxide (type OMS-2) for the abatement of oxygenated VOCs

Two solids were synthesized by the reaction between Mn2+ and KMnO4 in different order. The results of the characterization of both solids showed that: (i) they are poorly crystalline, although both belong to the Cryptomelane (OMS-2) phase; (ii) these materials are mesoporous (mesopores concentration in the order of 80%); (iii) they contain the couple Mn3+/Mn4+, being the Mn3+ concentration a function of the preparation method. Both catalysts were analyzed in the total oxidation of ethanol and the percentage of ethanol conversion on both solids reached 50% at 155 degrees C. The adsorption studies of methanol and ethanol have demonstrated the presence of basic sites and two different adsorption sites. The analysis of the results suggest that the amount of adsorbed ethanol molecules and the lowest temperature of CO2 desorption detected is due to the Mn3+ concentration. This phenomenon is ascribed to a high concentration of Mn3+ which could originate a weak Mn-O bond and the formation of more active oxygen species which would improve the catalytic performance. (c) 2007 Elsevier B.V. All rights reserved

Removal of VOCs by catalytic process. A study of MnZnO composites synthesized from waste alkaline and Zn/C batteries

Spent alkaline and zinc-carbon batteries were subjected to a biohydrometallurgy process, in order to recover manganese and mixed manganese zinc oxides. Two solids were synthesized, one of them prepared by reaction of MnSO4 and KMnO4 (MnOx) and the other obtained by chemical precipitation with NaOH (ZnMnO). The characterization by XRD, TPR, FTIR and XPS revealed the presence of Mn3+ and Mn4+ cations in both samples, and the presence of ZnO and Mn-Zn spinels in ZnMnO. The samples were evaluated in the oxidation reaction of ethanol and toluene. The results in the flow reactor showed that ethanol conversion on both catalysts, MnOx and ZnMnO, is rather similar, but toluene conversion is markedly higher on MnOx, due to a greater Mn/Zn ratio and to the absence of a crystallized ZnO phase. The FTIR study demonstrated that ethanol is oxidized to acetaldehyde at low temperature, and to CO2 and CO at 400 \ub0C. Traces of CH4 in the gas phase are also detected at high temperature. The formation of ethoxy and acetate groups is observed at the catalyst surface. With respect to toluene oxidation, CO2 is detected at 300 \ub0C and when the temperature is increased, CO is also observed in the gas phase. The results showed that: (i) the alkaline and Zn-carbon batteries can be recycled as catalysts and (ii) the solids can be used in the catalytic process for VOCs control