Synthesis, characterisation and catalytic applications of sol–gel derived silica–phosphotungstic acid composites Original Research Article

Phosphotungstic acid (HPWA)–silica composites were synthesised upto 80 wt.% HPWA loading both by conventional impregnation and sol–gel incorporation techniques. The samples were characterised by BET, XRD, NMR, FT-IR and TG. A comprehensive study on the effect of HPWA loading on the acidity has been performed using pyridine adsorption, NH3 TPD and a catalytic test reaction. The samples containing 50 wt.% HPWA showed the best overall performance. Although, the acidic properties of the impregnated catalysts were superior to their sol–gel counterparts, stability measurements (XRD, FT-IR and test reaction) performed before and after washing the samples with H2O/EtOH mixture have unambiguously proved that the sol–gel derived composites are more suitable for the purposes of heterogeneous catalysis.