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

Abstract

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.

Comments on “Use of Rh (III)-Heteropolymolybdate as Potential Catalysts for the Removal of Nitrates in Human Drinking Water: Synthesis, Characterisation and Catalytic Performance” by María A. Jaworski et al. (Water Air Soil Pollut (2018) 229: 309)

“…An aspect that we believe is missing in Figures 7 and 8 in (Jaworski et al 2018) is the typical plot of the concentration evolution with time of byproducts nitrites and ammonium. Given the importance of the concentration of these species in human health, their evolution with time appear in many research articles on the topic of nitrate reduction via catalysis.…”

“…Therefore, our understanding on catalytic hydrogenation research is that it should not only investigate the potential of nitrate reduction by some catalysts under study, but also to guarantee that the concentrations of all toxic and unwanted byproducts are below the guideline limits. We are providing below some comments on several particular aspects presented in (Jaworski et al 2018) in their Introduction, Results and Conclusion sections.…”

Textural Characterization by Using an Alternative Langmuir Isotherm and a New Thickness Function

“…The system was kept at 25 °C in a thermostated bath for 30 min. The resulting sample was defined as Dt …”

“…Chemical composition measurements were made using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM EDS) by using a Philips SEM 505 microscope with a dispersive energy system for microanalysis by using an X-ray, EDAX 9100. Fourier-transform infrared spectroscopy (FTIR) was performed through FTIR spectrometer Bruker IFS 66 equipment, by using KBr pellets in the 4000–400 cm –1 range. ,,− …”

“…The resulting sample was defined as Dt. 39 Zeolites. A natural Argentinean Clinoptilolite type zeolite of the natural, from La Rioja, Argentina was used.…”