Selective gas phase hydrogenation of nitroarenes over Mo2C-supported Au–Pd

Abstract

We report the first synthesis of Mo₂C-supported Au and Au–Pd catalysts (nominal Au/Pd = 10 and 30) obtained from colloidal nanoparticles stabilised by polyvinyl alcohol (PVA). Equivalent Au/Al₂O₃ and Au–Pd/Al₂O₃ were prepared and served as benchmarks. Residual PVA was removed by thermal treatment in N₂, which was monitored by thermogravimetric analysis. The catalysts were characterised in terms of temperature-programmed reduction (TPR), BET surface area, H₂ chemisorption, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) measurements. The reduced catalysts exhibited an equivalent metal particle size range (1–8 nm) and mean size (4–5 nm). The carbide samples showed greater H₂ chemisorption capacity than the Al₂O₃ systems where inclusion of Pd enhanced H₂ uptake. XPS measurements suggest electron transfer from Al₂O₃ to Au while the Au binding energy for the carbide samples is close to that of the metallic Au reference. The catalysts were tested in the gas phase hydrogenation of nitrobenzene, p-chloronitrobenzene and p-nitrobenzonitrile and delivered 100% selectivity to the target amine in each case. Inclusion of Pd served to increase selective hydrogenation rates where Au–Pd/Mo₂C outperformed Au–Pd/Al₂O₃, a response that is attributed to increased surface hydrogen.