MIL-101(Cr) Supported Pt and Au-Pt Composites As Active Catalysts for the Selective Hydrogenation of Nitrobenzene under Mild Reaction Conditions

In this study, we report the successful synthesis of monometallic Pt(2 wt.%)/MIL-101(Cr) and bimetallic Au(1 wt.%)-Pt(1 wt.%)/MIL-101(Cr) catalysts with low dimension MeNPs by the double-solvent (DS) method. The catalysts were characterized by powder X-ray diffraction (PXRD), N2 sorption analysis (BET), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and transmission electron microscopy (TEM). The characterization results demonstrated the presence of well-dispersed Pt and Au-Pt nanoparticles (2.9 and 2.7 nm, respectively), located mainly inside the pores of MIL-101(Cr). The stronger interaction of Au-Pt NPs with the support compared to Pt NPs was demonstrated by H2-TPR and XPS, which proved the existence of charge exchange between Pt NPs and Cr from MIL-101 in the case of Au(1 wt%)-Pt(1 wt%)/MIL-101(Cr), but not in the case of Pt(2 wt%)/MIL-101(Cr). The composite materials were tested in the catalytic selective hydrogenation of nitrobenzene to aniline in liquid phase under mild conditions (low temperature, low hydrogen pressure), and in the presence of a biomass-derived non-toxic solvent (ethanol). The bimetallic Au(1 wt%)-Pt(1 wt%)/MIL-101(Cr) catalyst showed superior catalytic activity as compared to the monometallic Pt(2 wt%)/MIL-101(Cr) catalyst. This is due to the synergetic effect between the two metals as demonstrated by the projected density of states studies.