Efficient base-free oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over a Ru/CaY molecular sieve catalyst

Abstract

As a vital platform compound for renewable plastics, coatings, and pharmaceuticals, 2,5-furandicarboxylic acid (FDCA) has increasingly drawn interest for its green and efficient production. In this study, a cost-effective NaY molecular sieve with a high Si/Al ratio was used as the support to prepare CaY molecular sieve via ion exchange, followed by the loading of ruthenium nanoparticles using an impregnation–reduction method to obtain the Ru/CaY catalyst. Structure-activity relationship studies revealed that the high dispersion of Ru nanoparticles enhanced the accessibility of active sites on the catalyst surface. The introduction of Ca²⁺ increased the basicity of the support, synergistically promoting the oxidation of HMF, while the structural stability and high specific surface area of the molecular sieve framework provided a favorable environment for Ru dispersion. Under base-free conditions, optimized oxygen pressure (0.5 MPa), reaction temperature (120 °C), and reaction time (11 h), the 4 wt% Ru/CaY (1:1) catalyst achieved efficient catalytic oxidation of 5-hydroxymethylfurfural (HMF), achieving a 100% conversion rate and 91.4% FDCA yield. Furthermore, after five consecutive reaction cycles, maintaining an FDCA yield of 85.2%, and after regeneration treatment, the FDCA yield was restored to 90.2%, demonstrating excellent reusability. This study offers an efficient strategy for the base-free oxidation of HMF and establishes a solid foundation for the green, scalable synthesis of FDCA.