Pt nanoparticles entrapped in mesoporous metal–organic frameworks MIL-101 as an efficient catalyst for liquid-phase hydrogenation of benzaldehydes and nitrobenzenes

• Hydrogenation of benzaldehyde, nitrobenzene and derivatives with Pt catalysts.
• Pt/MIL-101 was more efficient than Pt/Al2O3@SBA-15 in water for these reactions.
• The TOF obtained with Pt/Al2O3@SBA-15 was less than a half of that with Pt/MIL-101.
• High hydrophobicity of MIL-101 can enrich substrates around Pt/MIL-101 catalyst.

Metal organic-framework MIL-101 and inorganic mesoporous composites Al2O3@SBA-15 supported Pt catalysts, Pt/MIL-101 and Pt/Al2O3@SBA-15 catalysts, were prepared and characterized by means of X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), CO chemisorption and thermo-gravimetric (TG) analysis. Pt nanoparticles were highly dispersed on both supports. In liquid-phase hydrogenation of nitrobenzene, benzaldehyde and their derivatives, the Pt/MIL-101 catalyst was superior to the Pt/Al2O3@SBA-15 catalyst in water. For liquid-phase hydrogenation of nitrobenzene with the Pt/MIL-101 catalyst, owing to high solubility of nitrobenzene in ethanol, the reaction in ethanol went much faster than that in water, furnishing a turnover frequency (TOF) in ethanol up to 18,053 h−1, almost triple of that obtained in water under similar conditions. The highest TOF of 25,438 h−1 was obtained in ethanol for hydrogenation of 3-chloro-nitrobenzene with the Pt/MIL-101 catalyst. As for hydrogenation of benzaldehyde series, 2-fluoro-benzaldehyde and 3-fluoro-benzaldehyde gave the highest TOFs of 5146 h−1 and 3165 h−1 in water with the Pt/MIL-101 and Pt/Al2O3@SBA-15 catalysts, respectively. We deduce that surface property of MIL-101 with high hydrophobicity is helpful to enrich reactants around the Pt/MIL-101 catalyst in water, where nitrobenzene or benzaldehyde and its derivatives have a limited solubility, so that high catalytic performance was achieved with the Pt/MIL-101 catalyst in water. Of particular note is that the Pt/MIL-101 catalyst can be reused at least four times without loss in activity or selectivity.

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