Effect of promoter and noble metals and suspension pH on catalytic nitrate reduction by bimetallic nanoscale Fe-0 catalysts

Abstract

Experiments were conducted to investigate the effect of experimental factors (types of promotor and noble metals, H-2 injection, and suspension pH) on catalytic nitrate reduction by bimetallic catalysts supported by nanoscale zero-valent iron (NZVI). NZVI without H-2 injection showed 71% of nitrate reduction in 1h. Cu/NZVI showed the almost complete nitrate reduction (96%) in 1h, while 67% of nitrate was reduced by Ni/NZVI. The presence of noble metals (Pd and Pt) on Cu/NZVI without H-2 injection resulted in the decrease of removal efficiency to 89% and 84%, respectively, due probably to the electron loss of NZVI for formation of metallic Pd and Pt. H-2 injection into Cu-Pd/NZVI suspension significantly improved both catalytic nitrate reduction (>97% in 30min) and N-2 selectivity (18%), indicating that adsorbed H on active Pd sites played an important role for the enhanced nitrate reduction and N-2 selectivity. The rapid passivation of NZVI surface resulted in a dramatic decrease in nitrate reduction (79-28%) with an increase in N-2 selectivity (8-66%) as the suspension pH increased from 8 to 10