Intrinsic activity of interfacial sites for Pt-Fe and Pt-Mo catalysts in the hydrogenation of carbonyl groups

Abstract

Bimetallic PtFe/SiO2 and PtMo/SiO2 catalysts were prepared using controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl and (cycloheptatriene)molybdenum tricarbonyl on a Pt/SiO2 parent material. These catalysts were studied for the hydrogenation of ketone and aldehyde groups. Selective deposition of Fe onto Pt nanoparticles via the CSR method was confirmed by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The oxidation states of the Pt and Fe species for PtFe catalysts were determined following treatment in H2 at 573 K using X-ray photoelectron spectroscopy, showing that the dominant Pt phase is metallic Pt, while Fe is present in the metallic and +2 oxidation states, and Mo is present as a mixture of metallic, +4, and +6 oxidation states. The turnover frequency (TOF) of a Pt site for acetone (ketone) hydrogenation at 353 K and atmospheric pressure is 0.9 min−1, whereas the TOF values of Pt-FexOy and Pt-MoOx sites are 93 and 76 min−1, respectively. For the hydrogenation of 2-hydroxytetrahydropyran (2-HY-THP, aldehyde) at 393 K and 30 bar pressure, the TOF of a Pt site is 7.8 min−1, while the TOF values of Pt-FexOy and Pt-MoOx sites are 480 and 830 min−1, respectively. The order of magnitude enhancement of the TOF on the Pt-FexOy and Pt-MoOx interfacial sites compared to that of the Pt site suggests that the Pt-metal oxide interface created on Pt catalysts by selective addition of Fe and Mo are active sites for both acetone and 2-HY-THP hydrogenation reactions. The presence of interfacial sites may enhance the catalytic activity over PtFe/SiO2 and PtMo/SiO2 catalysts by stabilization of adsorbed reactive intermediates through bonding with CO groups.