Electrochemical reduction of NOx species at the interface of nanostructured Pd and PdCu catalysts in alkaline conditions

[Display omitted] •The synthetized nanoparticles have an average size of 12 nm (Pd) and 3 nm (PdCu).•The incorporation of copper improves the NOx electro-reduction process.•The PdCu/C catalyst exhibit the best electroreduction performance for all solutions.•Catalysts with a low noble metal amount was used for an efficient NOx reduction.•Coupling with DEMS it has been demonstrated the production of N2, NH3and N2H4. Electrochemical reduction of NOx species such as nitrates (NO3−), nitrites (NO2−), nitric oxide (NO), nitrogen dioxide (NO2) and their mixtures, was studied at the interface of palladium (Pd) and palladium-copper (PdCu) nanoparticles supported on carbon Vulcan (C). The electro-catalysts were synthesized by impregnation route with a low noble metal content of 5% wt. Pd and 2.5% wt. Pd for the mono and bi-metallic electrocatalyst, respectively. It was found by XRD analysis the formation of a solid solution in the bi-metallic catalyst and the TEM analysis suggest that the incorporation of copper decreases the particle size from 12 to 3 nm in comparison with its counterpart free of copper. Also, XPS technique verify the presence of Pd and Cu species in their metallic-oxidation states. Linear sweep and cyclic voltammetry techniques were used for the evaluation of the electrochemical NOx reduction, using alkaline solutions of NO2− or NO3− saturated with NO2 (synthesized in-situ) and NO (from commercial source). The results showed that the catalytic-activity at the current versus potential (i-E) characteristics improves significantly due to the presence of copper (as also demonstrated by CO-stripping-electrochemical active surface area calculations), inhibiting the process associated with the hydrogen evolution reaction. It is also noted in this work that the reduction faradic-current is c.a. 6 times higher at saturated solutions with NO and NO2. The NOx species were reduced mainly to nitrogen, ammonia and hydrazine as confirmed using on-line differential electrochemical mass spectrometry (DEMS) during steady-state experiments.