Hydrotalcite-supported Pd-Cu catalyst for nitrate adsorption and reduction from water

Hydrotalcite-supported Pd-Cu catalyst for nitrate adsorption and catalytic reduction from water is prepared by co-impregnation method and characterized by surface area (BET), X-ray diffraction (XRD), scanning electron microscope (SEM), trans- mission electron microscope (TEM) and X-ray pho- toelectron spectrum (XPS). The performance of ad- sorption and hydrogenation of nitrate was evaluated and compared with Al2O3, TiO2, and HZSM-supported Pd-Cu catalysts. The experimental results demon- strated that hydrotalcite-supported Pd-Cu catalyst exhibited a high surface area (185.3 m2/g) and mesopore structure (average pore diameter of 52.2 ?). The active metal clusters were homogeneously dispersed on the support, and the size of the most was less than 10 nm. Excellent adsorption for nitrate resulted from that nitrate ions were forced to enter the interlayer space when the calcined hydrotalcite re- generated layer structure in nitrate solution. The ad- sorption isotherm could be well described by the Langmuir model. The comparison between the ad- sorption and catalytic hydrogenation for nitrate using hydrogen indicated that nitrate reduction on hydro- talcite-supported Pd-Cu catalysts was a consecutive and dynamic adsorption and catalytic hydrogenation process. Compared with the Al2O3, TiO2, and HZSM- supported catalysts, hydrotalcite-supported Pd-Cu catalyst possessed higher catalytic activity and se- lectivity. The analysis on the dissolving of metals in the solution demonstrated that there was hydrolyza-tion on the surface of the hydrotalcite-supported Pd-Cu catalyst. However, the concentrations of dis- solved metals in the solution were lower than the standard executed in China. The activity of the hy- drotalcite-supported Pd-Cu catalyst for nitrate reduc- tion kept steady after repeated use.