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

In this paper, substituted anilines are industrially obtained by direct hydrogenation of nitroaromatic compounds with molecular H(2) 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/SiO(2), Cu/SiO(2) and Pd/SiO(2,) and with bimetallic CuNi/SiO(2) and CuPd/SiO(2) catalysts, both in the absence and presence of H(2), 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/SiO(2) catalyst with a Pd enriched surface is prepared that exhibits an enhanced H(2) dissociation ability and a particular reactivity at the boundary between the two metals.