Characterization of (Sn and Cu)/Pd catalysts for the nitrate reduction in natural water

The aim of this work is to characterize different (Cu and Sn)/Pd catalysts, supported on alumina, used for the catalytic removal of nitrates in natural water. The catalysts have been prepared with a Pd/(Cu or Sn) ratio of 2 but with different metal contents. Their activity and selectivity have been studied using a continuous stirred-tank reactor with nitrate polluted water from an aquifer. The catalysts have been characterized both before and after reaction by XPS, XRD, XRF, adsorption–desorption N2 isotherms at 196 °C and TEM. XPS results show changes of the Pd/Sn surface atomic ratio upon catalyst activation and after reaction and the coexistence of different oxidation states for the active metals. The studied catalysts are active, being the catalyst with the best performance that with the highest metallic dispersion and with the lowest phases segregation. The characterization of the catalysts after reaction shows that catalyst deactivation could be related with the non-reversible oxidation of the Sn–Pd couple.

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► Pd/Sn catalysts supported on alumina are characterized by XPS and other techniques.
► The Pd/Sn surface atomic ratio change upon catalyst activation and after reaction.
► The most active catalyst is 0.5% Sn–1% Pd supported on high surface area Al2O3.
► Deactivation is due to irreversible Sn–Pd oxidations or to competitive adsorptions.