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Graphical abstract Highlights • Ir supported on SiO 2 was investigated for 5-hydroxymethylfurfural (HMF) conversion. • Hydrogenation route from HMF to 2,5- bis -(hydroxymethyl)furan (BHMF) was preferred. • Ir dispersion combined with acid sites and H 2 SO 4 promoted 2,5-dimethylfuran formation. • High activity to value-added products was achieved over Ir supported on SiO 2. Abstract Catalytic performance of iridium supported on SiO 2 was investigated for 5-hydroxymethylfurfural (HMF) transformation. Ir/SiO 2 catalysts exhibiting different metal loading (1, 3, and 5 wt.%) were tested in the preliminary experiments in the hydrogenation of two probe molecules, e.g. ethyl pyruvate (EP) and ketopantolactone (KP) to evaluate the Ir dispersion on the catalyst activity in C O hydrogenation. In the transformation of HMF the influence of metal dispersion, iridium precursor and addition of H 2 SO 4 were studied revealing that 2,5- bis -(hydroxymethyl)furan (BHMF) was the main product with 83% selectivity at 70% conversion of HMF over chlorine free Ir/SiO 2 together with H 2 SO 4 at 333 K in THF under 10 bar H 2 pressure. On the other hand, one-pot synthesis of HMF to 2,5-dimethylfuran (DMF) was promoted in the presence of chlorine containing 1%Ir/SiO 2 (Cl) and H 2 SO 4. Both of these products are considered high value-added chemicals from biomass-derived 5-hydroxymethylfurfural. The exposed iridium atoms together with the total acid sites are an important catalytic descriptor for hydrogenation of HMF to BHMF. [ABSTRACT FROM AUTHOR]

The lively acidic properties in water of niobium phosphate (NBP) catalyst and NBP modified samples by acidic treatments in HCl solutions at 0.1, 1.0, and 10 M concentration (NBP01, NBP1, and NBP10, respectively) have been exploited for the direct conversion reaction of cellobiose to hydroxymethylfurfural (HMF) at temperature of 80–130 °C. Acidity of the samples was determined by liquid-solid titrations working in a modified HPLC line with basic solutions of phenylethylamine (PEA), used as a base probe. As solvents, an apolar-aprotic one, cyclohexane, was used for determining the intrinsic acidity and water for the effective acidity. In addition, pyridine/water co-adsorption FT-IR experiments complemented the acidity study, and the results obtained confirmed the presence of both water-tolerant Lewis acid sites (LAS) and some residual Brønsted acid sites (BAS) on all the NBP samples. On NBP, the LAS to BAS ratio was 1.69, measured in cyclohexane, and only slightly decreased to 1.30, when measured in water. Catalytic activity was studied in a liquid-solid reaction line with fixed bed flow reactor working in complete recirculation. The reaction of HMF formation from cellobiose consists of three distinct catalytic actions: hydrolysis of the β-1,4-glycosidic bonds of cellobiose, isomerization of the formed glucose monomers to fructose, and cyclo-dehydration of fructose to HMF. Comparative catalytic results obtained with a sulfonic acid resin (Amberlite IR 120) showed that it was not able to form any HMF from cellobiose in the range of temperature studied, only cellobiose hydrolysis to glucose can be successfully achieved on the protonic acid resin. [ABSTRACT FROM AUTHOR]

• Multifunctional nanocomposites with non-precious metals and magnetic core. • Catalysts combine Nb-MCM-41 and Mn, Co and Fe oxides as a shell. • Selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. • The new developed catalysts do not require the presence of a base. • Catalysts combine unique oxidation properties with practical separation advantages. The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has been investigated on multi-functional magnetic nano-composite catalysts (10M@xNb@MNP, where M = CoO x , MnO x or FeO x , "10" - 10wt% and x = Si/Nb ratio of 50 and 22) combining Nb-MCM-41 and Mn, Co and Fe oxides as a shell of a magnetic nanoparticles core. These catalysts were exhaustively characterized by several techniques such as XRD, adsorption-desorption of liquid nitrogen at 77K, CO 2 - and NH 3 -TPD, DRIFT, XPS, SEM-EDX, ICP-OES and ToF-SIMS. The new composite catalysts produced FDCA with a selectivity of 96.5 % for a X HMF = 96.9 % (10Co@22Nb@MNP). A synergetic effect between MO x and Nb species in the activation of t -BuOOH and oxidation of HMF has been identified. The new developed catalysts do not require the presence of a base in the homogeneous phase and combine unique oxidation properties with practical separation advantages. [ABSTRACT FROM AUTHOR]