A new molecular pathway allows the chemoselective reduction of nitroaromatics on non-noble metal catalysts

Abstract At difference with noble metals, the oxophylic character of non-noble metals strongly facilitates the rupture of the N O bonds in nitrobenzene , yielding nitrosobenzene as primary reaction intermediate. By combining periodic DFT calculations and kinetic studies , a direct pathway involving successive dissociation of N O bonds followed by two hydrogenation steps, Ph-NO2 → Ph-NO → Ph-N → Ph-NH → Ph-NH2 , has been found as most favorable on Ni catalysts. The rate determining step of the global process is the hydrogen transfer to adsorbed Ph-N intermediate. The catalyst surface becomes partly oxidized during reaction, which favors the vertical adsorption of the nitroaromatic compounds and enhances selectivity, while total surface oxidation leads to catalyst deactivation . It is proposed that both catalytic activity and selectivity of Ni and, possibly, other non-noble metals can be tuned by controlling the degree of oxidation of the metal surface.