Catalytic hydrogenation of nitrate in water: improvement of the activity and selectivity to N₂ by using Rh(III)-hexamolybdate supported on ZrO₂–Al₂O₃
2022
Jaworski, María A. | Navas, Marisa | Bertolini, Guillermo R. | Peroni, María B. | Cabello, Carmen I. | Gazzoli, Delia | Casella, Mónica L.
Catalysts prepared on ZrO₂, Al₂O₃ and ZrO₂–Al₂O₃ (ZrAl-10) supported with Anderson heteropolyanion (RhMo₆) as active phase were investigated for the elimination of NO₃ ⁻ from water. Raman characterization of pure and supported RhMo₆ phase showed the presence of polymolybdic species of different degrees of complexity when RhMo₆ was supported. The temperature-programmed reduction study revealed the synergic effect between Rh and Mo species, through which the reducibility of Mo was promoted by Rh, and different phase/support interactions were verified. Among the supports, ZrAl-10 presented the highest acidity due to the presence of ZrO₂ in the tetragonal modification and high specific surface area (due to Al₂O₃), favouring rhodium–molybdenum active phase/support interaction and high dispersion. All catalysts prepared were active in removing NO₃ ⁻, the one prepared with the RhMo₆ phase on the ZrAl-10 support being the most active. These results point to the formation of an active surface with a high dispersion of Rh and Mo. The highest selectivity to N₂ (99.3) exhibited by the RhMo₆/ZrAl-10 catalyst is proposed to be related to the high Rh dispersion (0.755) and to the presence of Lewis acid sites (oxygen vacancies) of the tetragonal ZrO₂ modification that favour NO₃ ⁻ adsorption through electrostatic interactions.
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