Synergistic catalysis in loaded PtRu alloy nanoparticles to boost base-free aerobic oxidation of 5-hydroxymethylfurfural

The synergistic catalysis of dual metal sites is vital for selective activation of complicated chemical bonds in biomass compounds. The base-free selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) using air as oxidant and water as solvent is a highly sustainable upgrading process for cellulosic carbohydrates. In this work, a series of Pt_xRu-MgAlO (x = 0.5, 1, 2 and 3, in mole) nanocatalysts with controlled particle sizes (ca. 2 nm) were synthesized by a PVP-assisted adsorption method. The Pt₂Ru-MgAlO catalyst showed 99% selectivity of FDCA with full conversion of HMF at only 100 °C under 0.2 MPa of air. In the meantime, an initial reaction rate of HMF of 2.8 mmol mol_M⁻¹ s⁻¹ and an intrinsic turnover frequency of 61.5 h⁻¹ were attained, respectively. Besides, this catalyst exhibited superior stability during five consecutive reuses without metal leaching. It was disclosed that the Pt-Ru interaction played critical roles in determining the intrinsic activity and the CO bond activation of the prepared Pt_xRu-MgAlO catalysts. Kinetic experiments combined with in situ chemisorption techniques clearly unraveled adsorption and activation processes of CO bond on Pt⁰-Ru⁰ sites. To the best of our knowledge, this work firstly reported a PtRu bimetallic catalyst for aerobic oxidation of HMF and provided insight into synergistic catalysis.