Hydrogenations of nitrate and nitrite in water over Pt–promoted Ni catalysts

Abstract

Hydrogenations of nitrate (NO 3 −) and nitrite (NO 2 −) in water were studied with 40–5000 ppm of the reactant at 333 K using a gas–liquid flow reactor over Pt–promoted Ni catalysts. Porous Ni was highly active for hydrogenation of NO 3 − to form NH 3 exclusively, but rapid deactivation was observed during the reaction. It was found that the addition of a small amount of Pt to the porous Ni greatly enhanced the stationary activity. The loading amount of Pt was sensitive to the activity; 1 wt.% Pt–Ni exhibited the maximum activity. XPS measurements revealed that Pt suppressed the oxidation of the Ni 0 atoms on the surface. The kinetic equation, v = k[NO 3 −] 0.8 PH 2 0.8, was obtained for the hydrogenation of NO 3 − over 1 wt.% Pt–Ni. Results showed that 1 wt.% Pt–Ni was highly active and stable even for 5000 ppm of nitrate without the dissolutions of Pt and Ni. The product was mainly NH 3 over Pt–Ni, independent of the concentration of NO 3 − or NO 2 −, the pressure of hydrogen or the reaction temperature.