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

Reisel Millán,Patricia Concepción,Cristina Cerdá Moreno,Mercedes Boronat,María Dolores Soriano

doi:10.3390/nano11082037

Abstract

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/SiO2, 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.

Highlights

IntroductionFigure 6), displaces adsorbed nitrobenzene in such a way that the two O atoms of the nitro group are directly bonded to two Cu atoms, but the molecule is partly bent due to some interaction between the aromatic ring and the surface Pd atoms
Based on previous theoretical studies proposing that nitrobenzene hydrogenation on noble and non-noble metals follows different pathways, in this work, mono- and bimetallic catalysts based on Ni, Cu and Pd have been synthesized, characterized and their interaction with nitrobenzene and H2 has been investigated by Infrared spectroscopy (IR) spectroscopy and density functional theory (DFT) calculations
It has been confirmed by IR spectroscopy that nitrobenzene is directly converted into nitrosobenzene on large Ni particles supported on SiO2, and that the addition or coadsorption of H2 results in the formation of aniline, following the mechanism proposed theoretically in ref

Summary

Introduction

Figure 6), displaces adsorbed nitrobenzene in such a way that the two O atoms of the nitro group are directly bonded to two Cu atoms, but the molecule is partly bent due to some interaction between the aromatic ring and the surface Pd atoms. Pd atoms in Pd6 Cu(111), Pd8 Cu(111) and Pd10 Cu(111) models, occupying positions in the uppermost layers of the model, enhances the interaction through the aromatic ring and two uppermost layers of the model, enhances the interaction through the aromatic ring results in de-coordination of of thethe nitro with adsorption adsorption and results in de-coordination nitrogroup groupfrom fromthe the catalyst catalyst surface, surface, with geometries quite similar to that found on pure surface.

Methods

Results

Conclusion