Strategies toward catalytic biopolymers: Incorporation of tungsten in alginate aerogels

Abstract We report the synthesis of W-doped biopolymer aerogels with potential applications to catalysis. The biopolymers were based on alginate, a cost-efficient natural material, and were prepared in environmentally friendly water/ethanol solutions. Gelation of alginate was induced by crosslinking with Ca 2+ . The resulting wet-gels were impregnated with an ethanolic solution of the ditungsten complex [W 2 ( μ -OEt) 2 (OEt) 2 (EtOH) 2 Cl 4 ] ({W = W} 8+ ) and were dried with supercritical fluid (SCF) CO 2 to yield W-doped alginate aerogels containing 10% w/w tungsten. Dry materials were characterized with FTIR, SEM/EDS, TGA, N 2 porosimetry and He pycnometry. The bulk densities were low ( −3 ), porosities were high (96% v/v), as well as the BET surface areas (380 m 2 /g). Pyrolysis of those aerogels at 800 °C under Ar yielded carbon along with a mixture of calcium tungstates, i.e., CaWO 4 and Ca 3 WO 6 (weight ratio: 70:30), while pyrolysis under O 2 yielded the same tungstates, but with a different weight ratio (10:90). This can be a new process for Ca 3 WO 6 , which, due to its ordered double perovskite structure, is ideal for doping with metal ions, at relatively low temperature (800 °C versus >1000 °C in the literature).