Use of Rh (III)-Heteropolymolybdate as Potential Catalysts for the Removal of Nitrates in Human Drinking Water: Synthesis, Characterisation and Catalytic Performance

María A Jaworski,Guillermo R Bertolini,Guillermo J Siri,Carmen I Cabello,Mónica L Casella

doi:10.1007/s11270-018-3962-3

Abstract

The investigation and development of technologies to remediate water contaminated with NO3− are constantly increasing. An economically and potentially effective alternative is based on the catalytic hydrogenation of NO3− to N2. With this objective, bimetallic RhMo6 catalysts based on Anderson-type heteropolyanion (RhMo6O24H6)3− were prepared and characteri3ed in order to obtain well-defined bimetallic catalyst. The catalysts were supported on Al2O3 with different textural properties and on silica. The heteropolyanion-support interaction was analysed 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 RhMo6 Anderson phase and the supports. The RhMo6/G, (G: γ-Al2O3) 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 RhMo6/G with that corresponding to a conventional catalyst prepared through successive impregnation of both Rh (III) and Mo (VI) salts.

Highlights

Soils have been fertilised with NO3− to improve agricultural yields
Since the artificial synthesis of ammonia was achieved by the Haber process, it has been possible to produce nitrogen fertilisers, which are currently used in large quantities in agriculture (Haber and Le Rossignol 1910)
Aluminas occur in nature as hydroxides or hydrated mineral oxides, which through hydrotreating processes are transformed into gibbsite or bayerite, which happen to be the precursors of the so-called transition aluminas

Summary

Introduction

Soils have been fertilised with NO3− to improve agricultural yields. Since the artificial synthesis of ammonia was achieved by the Haber process, it has been possible to produce nitrogen fertilisers, which are currently used in large quantities in agriculture (Haber and Le Rossignol 1910). As a result of this intensive use of fertilisers, NO3− concentration has been constantly increasing in groundwater since 1950 (Costa et al 2012). 309 Page 2 of 12 to NO2− in the human body and NO2− favours the development of methemoglobinaemia, which is a deficiency of oxygen in blood that can put life in danger, especially for children under 6 months (Bblue baby syndrome^). When NO3− is transformed to NO2− in the human body, other reactions can take place. NO2− could react with amine compounds to form the so-called N-nitrosamines (NOC, N-nitroso compound), some of which have proven to be mutagenic and carcinogenic (Citak and Sonmez 2010)

Objectives

Results

Conclusion