PVP stabilized Pd nanoparticles (Pd NP) were prepared in ethylene glycol at three different NaOH/Pd ratios and characterized by XRD, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The Pd NP were applied in the aerobic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) in an alkaline aqueous solution (T = 90 A degrees C, pO(2) = 1 bar). The highest yield of FDCA (90 %) was obtained in the presence of Pd NP with a mean diameter of 1.8 nm, prepared with a 4:1 molar ratio of NaOH:Pd. Thus prepared Pd NP could be stored in their alkaline synthesis solution under ambient conditions and showed consistently good catalytic performances after up to one month storage time, in contrast to Pd NP prepared with 2:1 and 1:1 ratio and stored in neutral or acidic environment.