Isomerization of d-glucose to d-fructose over metallosilicate solid bases Original Research Article

The isomerization of glucose was studied in water at 100 °C in the presence of various metallosilicates as solid base catalysts, namely the titanosilicates ETS-10, ETS-4 and AM-4, a sodium yttrium silicate analogue of the mineral montregianite (AV-1), an alkali calcium silicate analogue of the mineral rhodesite (AV-2), and a calcium silicate analogue of the mineral tobermorite (TOB). Fructose yields in the range of 20–40% were obtained within 2-h reaction. These results are either similar to or better than those achievable with the commercial zeolite Na–X or aqueous NaOH. Depending on the nature of the catalyst, different factors account for deactivation, such as loss of crystallinity, sodium/potassium leaching and surface passivation. Two of the more promising materials, AV-1 and TOB, were quite stable under the reaction conditions, as evidenced by powder X-ray diffraction analyses for the fresh and used catalysts. The used TOB catalyst exhibited a steady performance when recycled and for AV-1 fructose yields increased in recycling runs. The activity of the solid bases, with the exception of AV-1, could be correlated with the basicity characterized by Knoevenagel condensation tests.