Control of selectivity in the reduction of nitrate by shielding of Pd–Cu/C catalysts with AOT

Abstract

Catalytic chemical reduction of nitrate without generating harmful nitrite and ammonium is still a challenge limiting the application of this technology to the production of drinking water. In this work a new approach was proposed based on shielding of Pd active sites in PdCu catalysts by sodium bis-2-ethylhexyl sulphosuccinate (AOT). To study this concept and the interactions between PdCu and AOT, carbon-supported PdCu catalysts were prepared by microemulsion using AOT as surfactant, and by incipient wetness impregnation followed by exposure to AOT. All the catalysts based on AOT showed lower activity in nitrate reduction than those prepared by ordinary incipient wetness impregnation, however ammonium generation was prevented thanks to shielding of Pd active sites by AOT. Bimetallic catalysts prepared by physically mixing Pd and Cu monometallic catalysts and exposure to AOT revealed a lower activity in nitrate reduction, which was ascribed to the interference of AOT in the Pd–Cu redox mechanism and lower hydrogen spillover. However, the catalysts maintained the ability to reduce nitrite with negligible production of ammonium, showing that shielding of Pd active sites can be an interesting approach to avoid nitrite and ammonium formation in nitrate reduction, but a compromise between activity and selectivity must be achieved.