Electro-reduction of NOx-species in alkaline medium at modified carbon-supported palladium nanoparticles with variable concentration of C-sp2: An in-situ mass-spectrometry approach

Electrochemical denitrification is a promising technology for removing NOx species due to its environmental impact. In this work, nanostructured palladium electrocatalysts (3.2-3.7 nm) stabilized with different compounds namely lignin, oleylamine, octylamine, and 2-methyl-2butanol supported on Vulcan carbon were synthesized from organometallic precursors for the electrocatalytic reduction of nitrated species. For this purpose, electrochemical techniques such as cyclic voltammetry at different concentrations of NaNO2 and NaNO3 (saturated with NO2 gas, synthesized in situ) in the alkaline medium were carried out. The current versus potential characteristic (i-E) showed that the as-synthesized Pd/lignin/C catalyst exhibited the highest activity in the reduction of NO2 and NO3, with hydrogen production at more negative potentials, as demonstrated by differential electrochemical mass spectroscopy (DEMS). Additionally, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicate the presence of metallic palladium and other PdyOx species well distributed on the carbon support matrix promoting different interfacial redox processes depending on the stabilizer in turn and the carbon hybridization namely, D-parameter (D = sp(2)/sp(3)).