Highly active and stable Ru-(OH)-based catalysts supported on Ni-manganite for the base-free aerobic oxidation o 5 -hydroxymethyl furfural to 2,5-furandicarboxylic acid in a noble water organic solvent system

A novel approach to converting elevated levels of 5-hydroxymethyl furfural (HMF) into 2,5-furan dicarboxylic acid (FDCA) was investigated in this study. This method demonstrated the capability to yield FDCA at a rate of 92% from a solution containing 5% HMF in a solvent blend of acetone and water. The oxidation of HMF occurred in the absence of a uniform base due to the heightened solubility of FDCA in this specific solvent blend. Various catalysts composed of Ru -doped Ni- manganite was synthesized, characterized, and applied in the oxidation of HMF. Introduction of Ni enhanced the stability of Mn at increased oxidation states, resulting in the formation of the selective spinel phase NiMn₂O₄. Examination via CO-chemisorption indicated effective dispersion of Ru on the Ni₁Mn₅ support, particularly upon the formation of the spinel phase. The inclusion of Ru facilitated the reduction of both Ni and Mn, showcasing distinct low-temperature reduction profiles with the augmentation of Mn content Analysis via X-ray Photoelectron Spectroscopy (XPS) revealed cooperative electronic interactions between Ru and the support. Additionally, XPS and Extended X-ray Absorption Fine Structure (EXAFS) studies confirmed the formation of positively charged Ru species as Ru-0 and RuOH, exhibiting valences of +3 and +4, respectively. The Ru/Ni,Mn6 catalyst demonstrated exceptional. oxidative activity towards FDCA owing to a high abundance of oxygen atoms within its lattice, as well as the dispersion and interaction of Ru with the support material.