Insights into bifunctional active sites of Pt–MoO3/TiO2 catalysts enabling selective hydrogenation of an amino acid

Abstract

Selective hydrogenation of amino acids to amino alcohols is a valuable transformation in the synthesis of pharmaceuticals, fine chemicals, and chiral building blocks. However, achieving high activity and selectivity under mild conditions remains challenging due to the need for simultaneous hydrogen activation and substrate coordination. Here, we report a series of Pt–MoO₃ bifunctional catalysts for the hydrogenation of L-alanine (Ala) to alaninol (AlaOH), with a focus on tuning metal–oxide synergy. Structural and electronic characterization studies by high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy reveal strong Pt–MoO₃ interactions, characterized by partial electron transfer. Catalytic tests reveal a volcano-type dependence on the Pt/Mo ratio, with the 4-Pt–MoO₃ catalyst achieving the highest performance. The experiments of H₂ temperature programmed desorption and in situ diffuse reflectance infrared Fourier transform spectroscopy combined with theoretical calculations support a bifunctional mechanism, in which Pt serves as the primary site for H₂ activation, while MoO₃ facilitates adsorption and stabilization of polar alanine. Further tuning via thermal treatments shows that the moderate treatment at 500 °C optimally balances the redox state of MoO₃ without compromising Pt dispersion, leading to enhanced hydrogenation performance. This work not only advances understanding of metal–oxide interfacial catalysis but also provides a rational design strategy for efficient and selective hydrogenation of amino acids.