Potential of mono- and bimetallic catalysts for liquid-phase hydrogenation of aqueous nitrite solutions

Liquid-phase reduction using a solid catalyst provides a potential technique for the removal of nitrites from waters. Activity and selectivity measurements were performed for a wide range of reactant concentrations and reaction conditions in an isothermal semi-batch slurry reactor operating at atmospheric pressure. The effects of catalyst loading and initial nitrite concentration on the reaction rate were also investigated. The Pd monometallic catalysts were found to be advantageous over the Pd-Cu bimetallic catalyst with respect to both reaction activity and selectivity. Minimum ammonia formation was observed for the Pd(1 wt. %)/γ-Al2O3 catalyst. The reaction kinetics was found to be dependent on the catalyst surface hydroxylation, which has also been confirmed by runs conducted in a continuous-flow monolith reactor.