Nanostructured Ni-MoCx: An efficient non-noble metal catalyst for the chemoselective hydrogenation of nitroaromatics

Abstract

Catalysts for chemoselective hydrogenation are of vital importance for the synthesis of various important chemicals and intermediates. Herein we developed a simple method for preparing a highly efficient Ni-MoCx nanocomposite catalyst via temperature-programmed carburization of a polyoxometalate precursor. X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) analyses indicate that the resulting mesoporous nanocomposite catalyst is made up of well-dispersed metallic nickel particles embedded in a MoCx matrix. This catalyst exhibits high activity and selectivity (> 99%) in the hydrogenation of various substituted nitroaromatics to corresponding anilines. The high efficiency is attributed to the intimate contact of the constituents favoring electron transfer and hydrogen adsorption. Dihydrogen is physisorbed on the carbide support and dissociates on the nickel particles, as evidenced by Mo K-edge X-ray absorption near-edge structure (XANES) spectra, density functional theory (DFT), and hydrogen-deuterium exchange. The remarkable catalytic performance of the catalyst could be traced back to the synergistic interaction between the Ni particles and the carbide support. In-situ infrared spectroscopy and DFT simulations indicated that the adsorption/activation of the nitro group is favored compared to that of other substituents at the aromatic ring. In recyclability tests, the Ni-MoCx nanocomposite showed no significant loss of catalytic performance in seven consecutive runs, indicating its robust nature.