Catalytic hydrogenation of nitrate in water: improvement of the activity and selectivity to N2by using Rh(III)-hexamolybdate supported on ZrO2-Al2O3

Catalysts prepared on ZrO2, Al(2)O(3)and ZrO2-Al2O3(ZrAl-10) supported with Anderson heteropolyanion (RhMo6) as active phase were investigated for the elimination of NO(3)(-)from water. Raman characterization of pure and supported RhMo(6)phase showed the presence of polymolybdic species of different degrees of complexity when RhMo(6)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 ZrO(2)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 RhMo(6)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 N-2(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 ZrO(2)modification that favour NO(3)(-)adsorption through electrostatic interactions.

Automated summary

In this study, catalysts supported on ZrO2, Al(2)O(3), and ZrO2-Al2O3(ZrAl-10) with Anderson heteropolyanion (RhMo6) as the active phase were investigated for the removal of NO(3)(-) from water. It was found that the ZrAl-10 support exhibited the highest acidity and dispersion, which positively affected the performance of RhMo active phase and the catalyst. Moreover, the RhMo6/ZrAl-10 catalyst showed the highest activity and selectivity, which could be attributed to the high dispersion of Rh and Mo as well as the Lewis acid sites of the tetragonal ZrO(2) modification.