Bifunctional Metal-Chitosan Composites as Catalysts for the Upgrade of Biomass Derived Molecules

Christine Khoury, Chemical Engineering , Technion, Haifa, Israel
Christine Warwar Damouny, Chemical Engineering , Technion, Haifa, Israel
Nassem Hayek, Chemical Engineering , Technion, Haifa, Israel
Oz Gazit, Chemical Engineering , Technion, Haifa, Israel

Chitosan (Cs) is a naturally abundant polysaccharide. It is insoluble in most organic solvents and water and is inherently functionalized with pendent hydroxyl and amino groups. These beneficial properties make him a prime candidate as a sustainable solid support. Hence, Cs has been used to support enzyme or metal based catalysts along with a range of adsorption applications. A prerequisite to obtain highly active Cs material is the prevention of its structure collapse, by the strong thermodynamic tendency to form inter- and intra- molecular hydrogen bonds.
In this work, we demonstrate a simple yet novel method for the preparation of high surface area of Cs based materials (currently up to 190 m2/g), without sacrificing important amine side chains. We do this by supporting the Cs framework with inorganic sites that prevent structure collapse without the use of traditional supercritical CO2 drying and even under high vacuum (10-3 mbar) and at 110 oC for over 12 hours. The general procedure entails dissolution of Cs, to open the chain structure, followed by dispersion in an aprotic solvent. The dispersed swollen Cs is then infiltrated with a metal precursor such as SnCl4, TiCl4 or SiCl4, which react chemically with the available hydroxyls. It was improved that by using this method inorganically crosslinking or grafting is occurred depending on the chosen solvent media.
Materials are characterized using XRD, ICP, TGA and FTIR. We show that by changing the solvent media we ca easily switch between protonated and deprotonated amine form. This is exploited to control the selectivity and reactivity of aldol-type condensation reactions. Catalytic results of aldol condensation will be presented.