Combined Spectroscopic and Computational Study of Nitrobenzene Activation on Non-Noble Metals-Based Mono- and...

In this paper, substituted anilines are industrially obtained by direct hydrogenation of nitroaromatic compounds with molecular H₂ using metals as catalysts. Previous theoretical studies proposed that the mechanism of the reaction depends on the nature of the metal used as a catalyst, and that rationally designed bimetallic materials might show improved catalytic performance. Herein, we present IR spectroscopic studies of nitrobenzene interactions with monometallic Ni/SiO₂, Cu/SiO₂ and Pd/SiO_2, and with bimetallic CuNi/SiO₂ and CuPd/SiO₂ catalysts, both in the absence and presence of H₂, combined with density functional theory (DFT) calculations on selected bimetallic NiCu(111) and PdCu(111) models. The results obtained experimentally confirm that the reaction mechanism on non-noble metals such as Ni proceeds through N-O bond dissociation, generating nitrosobenzene intermediates, while, on noble metals, such as Pd, H-attack is necessary to activate the NO bond. Moreover, a bimetallic CuPd/SiO₂ catalyst with a Pd enriched surface is prepared that exhibits an enhanced H₂ dissociation ability and a particular reactivity at the boundary between the two metals.