Electrochemically-mediated reactive separation of nitric oxide into nitrate using iron chelate.

Valorization of nitric oxide is a promising solution for addressing the environmental and resource issues related to the nitrogen cycle. However, low concentrations of nitric oxide combined with impurities in exhaust streams limit its potential, and it requires extensive energy to produce high-purity nitric oxide. Here, we propose a synergistic reactive separation system that combines iron-chelate selective absorption with an electrochemical reaction to convert nitric oxide to nitrate. Among the iron-based chelates tested, EDTA was found to be the most effective in capturing gas-phase nitric oxide. Direct electrochemical oxidation of Fe-EDTA-NO solution exhibited Faradaic efficiency and a partial current density toward nitrate of 70% and 30.1 mA cm-2 at 2.2 V vs RHE and pH 7, resulting in a 43-fold enhancement of nitrate partial current density and a 2-fold improvement in Faradaic efficiency compared to simple purging without selective absorbent. Nitrate was then selectively recovered from the Fe-EDTA system using simple polarity reversal following electrooxidation with a separation factor of 13 over background sulfate. This study offers a new approach to gas-phase NO remediation and valorization using an electrified means.

Effects of thermal aging on the electronic and structural properties of Pt-Pd and toluene oxidation activity.

Catalytic oxidation is a feasible method for remediating volatile organic compounds (VOCs), due to its lower energy consumption and mineralization of VOCs into H2O and CO2. Noble metal-based catalysts are preferred for the catalytic oxidation of VOCs because of their superior activity, but they are usually deactivated by thermal aging which sinters the metal particles. Here, we report that Pt-Pd/Al2O3 thermally aged at 700-900 °C in air showed enhanced catalytic activity for toluene oxidation in humid conditions. There were electronic and structural changes in the thermally aged Pt-Pd/Al2O3, as confirmed by numerous analyses. Both Pt and Pd existed in a metallic rather than oxidized state without additional reduction steps. The noble metal particles were assembled to form Pt-Pd alloy, in the form of isolated Pd atoms surrounded by Pt atoms. This specific alloy structure was found to be crucial to the observed enhancement in catalytic toluene oxidation at low temperature.

Dendritic Ternary Alloy Nanocrystals for Enhanced Electrocatalytic Oxidation Reactions.

Engineering the morphology and composition of multimetallic nanocrystals composed of noble and 3d transition metals has been of great interest due to its high potential to the development of high-performance catalytic materials for energy and sustainability. In the present work, we developed a facile aqueous approach for the formation of homogeneous ternary alloy nanocrystals with a dendritic shape, Pt-Pd-Cu nanodendrites, of which synthesis is hard to be achieved because of synthetic difficulties. Proper choice of stabilizer and fine control over the amount of stabilizer and reductant allowed the successful formation of Pt-Pd-Cu nanodendrites with controlled sizes and compositions. The prepared ternary alloy nanodendrites exhibited considerably improved electrocatalytic performance toward methanol and ethanol oxidation reactions compared to their binary alloy counterparts and commercial Pt and Pd catalysts, as well as to previously reported Pt- and Pd-based nanocatalysts because of synergism between their morphological and compositional characteristics. We anticipate that the present approach will be helpful to develop efficient electrocatalysis systems for practical applications.