Nitrate reduction by maghemite supported Cu-Pd bimetallic catalyst

We have investigated the catalytic nitrate reduction by maghemite supported Cu-Pd bimetallic catalyst (maghemite/Cu/Pd). 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 removal. 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 (99.5–83%) 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.

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► Maghemite/Cu/Pd showed excellent catalytic nitrate reduction (99.5%).
► Cu loading at 0.5 wt.% showed the highest N2 gas selectivity (43%).
► Pd loading at 0.25 wt.% showed the highest N2 gas selectivity (47%).
► Lower H2 flow rates enhanced N2 gas selectivity.
► Maghemite/Cu/Pd showed stable nitrate removal during three reaction cycles.