Effect of liquid property on adsorption and catalytic reduction of nitrate over hydrotalcite-supported Pd-Cu catalyst

Abstract

This study focused on investigating the effect of liquid property on adsorption and catalytic reduction of nitrate over hydrotalcite-supported Pd-Cu catalyst. Batch experiments were conducted under specific operating conditions. It was found that nitrate ions were adsorbed apparently by hydrotalcite-supported Pd-Cu catalyst at different reaction temperature (10, 25 and 35• C). Adsorption isotherms for NO 3 − were described by Langmuir's equation. Higher reaction temperature accelerated nitrate adsorption and reduction, and simultaneously decreased the accumulation of NO 2 − and NH 4 + . Nitrate adsorption and reduction were independent of the initial pH because of the high buffering capacity of hydrotalcite when the initial pH of solution was from 5.25 to 7.4. However, the dissolve of hydrotalcite-supported Pd-Cu catalyst at low initial pH (3.77) and higher concentration of OH − ions at high initial pH (10.74) decreased nitrate adsorption and reduction. When using various nitrate salts as a source of nitrate ions, nitrate adsorption and reduction removal efficiency decreased in the order: Fe 3+ > Mn 2+ > Mg 2+ > Ca 2+ > Na + , which was attributed to different affinity toward OH − . Co-existed cations in water with higher valence and lower crystal ionic radius and solubility constant of hydroxide showed stronger affinity toward OH − and consequently increased the concentration of active sites accessible to NO 3 − and NO 2 − . The competitive adsorption of Cl − , SO 4 2− and HCO 3 − with nitrate on the catalyst surface suppressed the adsorption and reduction of NO 3 − . Besides, few metals dissolved in neutral and alkaline solution. The activity of the hydrotalcite-supported Pd-Cu catalyst for nitrate reduction kept steady after repeated use.

Research progress of novel adsorption processes in water purification: A review

“…Accordingly, the current technologies used for nitrate removal from water receive an increasing attention. Based on the property of HT, a novel hydrotalcite-supported Pd-Cu material, combining the high adsorption capacity of HT and the reduction property of active metals (Pd-Cu) for nitrate, were developed (Wang Y, 2006;Wang et al, 2007a). In this case, HT was used not only as an adsorbent but also as a catalyst support.…”

Role of the Mg/Al atomic ratio in hydrotalcite-supported Pd/Sn catalysts for nitrate adsorption and hydrogenation reduction

“…Since the catalysts had excellent adsorptive ability toward anions, the nitrites concentration was to a much lower extent. In the previous study of our group, it was demonstrated that hydrotalcite-supported Pd/Cu catalysts had both excellent adsorption and catalytic properties for nitrate reduction [31,32]. Also, the catalyst synthesized via a coprecipitation method exhibited higher adsorption and catalytic activity than that prepared by coimpregnation method [31].…”

Nitrate reduction over a Pd-Cu/MWCNT catalyst: application to a polluted groundwater

“…on the metallic active sites [23][24][25], which led to a decrease in catalytic activity and selectivity. Wang et al [22] reported that, although a Cu-Pd/activated carbon catalyst showed high activity, selectivity for the formation of N 2 and N 2 O, and durability for the reduction of 100 mg/L NO − 3 in distilled water, the catalytic performance decreased in the case of the reduction of NO − catalyst deactivation.…”