(66h) Mechanistic Studies on the Electrocatalytic Reduction of Nitroaromatic Compounds

The reduction of nitroaromatic compounds is used in the synthesis of aniline (NH₂-phenyl) and phenylhydroxylamine (NHOH-phenyl) from nitrobenzene (NO₂-phenyl) for dye productions, pharmaceuticals, and other industrial chemicals. The reduction of nitroaromatics is environmentally important in the removal of toxins in wastewater, such as 2,4,6-trinitrotoluene (TNT). Electrochemical reduction methods can provide a low cost, selective, and efficient process using electrons and protons to drive reduction at ambient conditions. However, the electrocatalytic mechanism of nitroaromatic reduction across different electrocatalysts are not well established and are necessary to facilitate rational electrocatalyst design. We will present results from our density functional theory (DFT) investigation of nitrobenzene and other nitroaromatic compounds across M late transition metals surfaces (M = Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co, Ru, and Fe). Comparison are made between the inner-sphere electrocatalytic reduction process and the outer-sphere process, the non-catalytic mechanism.

The electrocatalytic reduction of NO₂-phenyl was investigated on the Fe (110) and Au (111) surfaces to determine the tradeoffs between using two metals with extreme differences in oxophilicity. Overall reduction activity is optimized based on a trade-off in activity for the initial reduction of the NO₂-phenyl* to NO-phenyl* and the reduction of surface-bound hydroxide (OH*) species. Using the binding of O as the surface descriptor, these two characteristic reactions were investigated across M late transition metals. As the binding energy of O strengthens on the metal surface, the initial adsorption and reduction of NO₂-phenyl* to NO-phenyl* becomes more favorable and the reduction of OH* becomes more difficult. DFT results predict that the Cu (111), Ir (111), Pd (111), and Pt (111) metal surfaces will most effectively balance these factors. We will compare results for nitrobenzene reduction with those of TNT, and also present results examining electroreduction mechanisms on Fe-based oxide surfaces.