Bimetallic catalysts supported on activated carbon for the nitrate reduction in water: Optimization of catalysts composition

The activities and selectivities of four pairs of bimetallic catalysts (Pd–Cu, Pt–Cu, Rh–Cu and Ir–Cu) supported on activated carbon were studied in order to optimize the metals composition for the reduction of nitrate in water with hydrogen. The catalytic tests were carried out in a semi-batch reactor, working at room temperature and pressure. The activity of the catalysts is quite different depending on the copper content. The maximum activity for the catalysts with 1% of the noble metal was obtained for 1%Rh–0.6%Cu, 1%Pd–0.6%Cu, 1%Pt–0.3%Cu and 1%Ir–0.3%Cu, with nitrate conversions after 5 h of reaction of 98%, 63%, 56%, and 55%, respectively. All these weight compositions correspond to an atomic ratio noble metal/copper close to 1. With the exception of the pair Ir–Cu, where the selectivity to ammonium is almost independent of the metals composition, for all the other cases it increases with the atomic copper content up to around 75%. The pair Rh–Cu was the most active among the bimetallic catalysts tested; however, significant amounts of ammonium are obtained. The nitrate conversions for the pairs Ir–Cu and Pt–Cu are similar but the former presents higher selectivities to ammonium. The pair Pd–Cu is the most selective in the transformation of nitrate to nitrogen.