Study on the synthesis of nanoporous hydrated zirconia applied to hydrothermal conversion of biomass-derived sugars

The synthesis of nanoporous hydrated zirconia catalysts was studied for application in the hydrothermal conversion of monosaccharides and biomass sources. The synthesis was carried out by sol-gel method using zirconium n-propoxide and Pluronic P123 as precursor and template, respectively. Different synthesis solvents, water (W), ethanol (E) and isopropanol (I), as well as different template removal methods, including thermal treatments and solvent refluxing extraction, were investigated. Physicochemical properties were determined by N-2 sorption, TEM, XRD, FTIR and potentiometric titration. Catalysts synthesized in alcoholic solvents by refluxing extraction exhibited high surface areas (320-360 m(2)/g) and pore volumes (0.20-0.43 cm(3)/g), which comprised large micropores and mesopores, and obtained the most outstanding acidic properties. A strong influence of the synthesis solvent on the amount and strength of acid sites was found, following the order I > E > W. This behavior was explained by different ratios between the basic terminal and acidic bridging Zr-OH bonds formed on hydrated zirconia. In tune with superior acidic and textural properties, promising mass yields towards lactic acid from a glucose, xylose and arabinose mixture (34.8 %), glyceraldehyde (83.36 %), starch (17.1 %) and wheat bran (18.3 %), were attained with the catalyst synthesized in isopropanol.