Search

A multifunctional hybrid material composed of W18O49 nanobelts (NBs), zirconium oxide, and Vulcan carbon (W18O49-ZrO2-C) has been used as support for platinum nanoparticles (PtWZC). For comparison, platinum supported on Vulcan carbon (PtC) was also synthesized. These catalysts were evaluated in the NO3- and NO2- (NOx) reduction reactions. The addition of W18O49 and ZrO2 to the carbon improved the size and distribution of the platinum nanoparticles. The electrochemical results showed that enhanced electrocatalytic activity for the NOx reduction was obtained on the PtWZC catalyst compared to PtC synthesized by the same technique and PtEtek from a commercial source. Our findings suggest that the adsorbed monatomic hydrogen (Hads) over platinum inhibits the reduction of nitrates and nitrites. Therefore, these reactions need a material that removes Hads from the surface or modifies it for the NOx reduction. The WZC support adsorbed monatomic hydrogen from water to form active bronze species (Hx-W18O49) that interacted with the NO3- and NO2- ions enabling their reduction, in accord with the results from in-situ Raman spectroscopy and Tafel slopes. N2, NO, NH3, and N2H4 products were detected in nitrite ion reduction by the Differential electrochemical mass spectrometry (DEMS) technique on the PtWZC catalyst. The production of N2 dominated in the cathodic and anodic scan. Hence, the novel catalyst can follow the indirect pathway, where the reduction process involves adsorption of NHx and adsorption of NO. The higher electrocatalytic activity obtained by the PtWZC catalyst was attributed to the uniform distribution of platinum on the support, the increased electrical conductivity produced by the W18O49 nanobelts, and the modulation of Hads on the surface.

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.