Nitrate reduction by Cu-Pd bimetallic catalyst

Abstract

We have investigated the catalytic nitrate reduction by maghemite and TiO2 supported Cu-Pd bimetallic catalyst (Maghemite/Cu/Pd and TiO2/Cu/Pd, respectively) and the effect of pH and zwitterionic buffer on cata-lytic nitrate reduction. In the chapter 3, BET, XRD, XPS, TPR, SEM/EDX, TEM analysis were carried out to characterize Maghemite/Cu/Pd. Remarkable nitrate removal (99.5%) by Maghemite/Cu/Pd was observed in 90 min, while Cu-Pd catalyst supported with alumina (43%) and hematite (63%) showed less efficient nitrate re-moval. Nitrate removal was excellent (> 95%) in all Cu loading variation (0.25-1 wt.%) on Maghemite/Cu/Pd, while selectivity of nitrogen gas formed during the reaction was the highest (43%) at a specific Cu/Pd ratio (0.5/0.5 wt.%). We also observed excellent nitrate removals (> 95 and > 94%, respectively) by Maghemite/Cu/Pd in the ranges of Pd loading (0.25-1 wt.%) and hydrogen flow rate (100-500 cc/min). The highest nitrogen selectivities (47 and 45%) were obtained by low Pd loading (0.25 wt.%) and hydrogen flow rate (200 cc/min). Maghemite/Cu/Pd showed slow decrease of nitrate removal (99.5 to 83%) and low metal leaching (1.5% of Cu leaching) during three reaction cycles. XPS analysis revealed that Cu(0) was oxidized to Cu2O and CuO during the catalytic nitrate reduction, while Pd(0) was not changed. In the chapter 4, TiO2/Cu/Pd was characterized via BET, XRD, SEM/EDX, TEM analysis. MES, MOPS, TRIS, TAPS, and CHES were selected to prepare pH range of 6 to 10. Nitrate reduction decreased from 100 to 26.3 % as pH increased from 6 to 10. Nitrite selectivity dra-matically increased in pH higher than 7 while ammonium and nitrogen gas selectivity decreased in higher pH range. Nitrate reduction at pH 8 prepared with TRIS buffer dramatically dropped (58.2 %) due to higher amount of Cu (35.2 %) and Pd (53.4 %) leaching leading deterioration of catalytic activity of TiO2/Cu/Pd. Increasing concentration of zwitterionic buffers negatively influenced on n...