Shanawar Hamid

Nitrate reduction on the surface of bimetallic catalysts supported by nano-crystalline beta-zeolite (NBeta)

Nitrate contamination of surface and groundwater is one of the most serious environmental issues due to its adverse effects on human health and the ecosystem. In this study, novel bimetallic catalysts supported by nanocrystalline beta zeolite (NBeta) were firstly developed for the complete and selective reduction of nitrate to environment-friendly nitrogen. The synthesis of a NBeta support and bimetallic catalysts was confirmed by X-ray diffraction and Fourier transformation infra-red spectroscopy. The morphology of the NBeta support and metal dispersion was confirmed by transmission electron microscopy and scanning electron microscopy with energy dispersive X-ray, which revealed that newly synthesized NBeta consisted of individually separated cubical shaped crystals and that the metals were well dispersed in uniform and closely packed ensembles. The nitrate reduction mechanism on NBeta-supported bimetallic catalysts was also identified by inductively coupled plasma mass spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction, and H2 pulse chemisorption. All catalysts successfully achieved 100% NO3− and NO2− removal. Sn–Pd-NBeta showed the highest reduction kinetics (k = 19.09 × 10−2 min−1) followed by In–Pd-NBeta (k = 2.89 × 10−2 min−1) and Cu–Pd-NBeta (k = 2.31 × 10−2 min−1). However, N2 selectivity was in the order of Cu–Pd-NBeta (92.68%) > In–Pd-NBeta (82.93%) > Sn–Pd-NBeta (80.80%). Characterization of the catalysts revealed that the highest N2 selectivity of Cu–Pd-NBeta was due to the suppression of a deep hydrogenation capacity of Pd by Cu. The NBeta-supported Cu–Pd, In–Pd, and Sn–Pd catalysts also showed a complete NO3− reduction with consistent N2 selectivity in successive and regenerated cycles. The results suggest an eco-friendly catalytic system which can be applied to the optimal ex situ remediation of water and wastewater contaminated with nitrate.

Effect of promoter and noble metals and suspension pH on catalytic nitrate reduction by bimetallic nanoscale Fe0 catalysts

ABSTRACT Experiments were conducted to investigate the effect of experimental factors (types of promotor and noble metals, H2 injection, and suspension pH) on catalytic nitrate reduction by bimetallic catalysts supported by nanoscale zero-valent iron (NZVI). NZVI without H2 injection showed 71% of nitrate reduction in 1 h. Cu/NZVI showed the almost complete nitrate reduction (96%) in 1 h, while 67% of nitrate was reduced by Ni/NZVI. The presence of noble metals (Pd and Pt) on Cu/NZVI without H2 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. H2 injection into Cu-Pd/NZVI suspension significantly improved both catalytic nitrate reduction (>97% in 30 min) and N2 selectivity (18%), indicating that adsorbed H on active Pd sites played an important role for the enhanced nitrate reduction and N2 selectivity. The rapid passivation of NZVI surface resulted in a dramatic decrease in nitrate reduction (79–28%) with an increase in N2 selectivity (8–66%) as the suspension pH increased from 8 to 10.