Exfoliated Layered Metal Oxide-Supported Ruthenium Catalysts for Base-Free Oxidation of 5-Hydroxymethylfurfural into a Renewable Bioplastic Precursor

2,5-Furandicarboxylic acid (FDCA) is a potential biopolymer precursor for polyethylene furanoate production. This study focused on synthesizing FDCA via catalytic oxidation of 5-hydroxymethylfurfural (HMF) over Ru-based catalysts supported on exfoliated MgAl-double oxides (LDO) for the first time in a homogeneous base-free system. Effects of the exfoliation solvent, preparation method, and Ru loading level on the physicochemical and catalytic properties of the resulting catalysts were investigated. The exfoliated LDO-supported Ru catalysts exhibited enhanced textural properties, RuOx dispersion, and basicity, resulting in better catalytic activity (at least 6 times higher FDCA yield) than conventional LDO-supported Ru catalysts in the conversion into FDCA. The Ru-based catalyst supported on an exfoliated LDO/carbon nanocomposite, Ru(3)/ESV-LDC, revealed the nearly complete HMF conversion (99.2%) at an FDCA selectivity of >98%. This was attributed to the synergistic effect derived from good RuOx dispersion, providing a high proportion of lattice oxygen for boosting surface oxygen mobility, and high basicity, in terms of both strength and number of basic sites. Moreover, Ru(3)/ESV-LDC exhibited good reusability without a significant loss of HMF conversion and FDCA yield, suggesting strong chemical robustness of RuOx species and a stable interaction between the active metal and support.