The environmentally friendly synthesis of heteropolyacids

Abstract

Fosfotungstic and fosfomolybdic Wells-Dawson heteropolyacids, H6P2W18O62.xH2O and H6P2Mo18O62.xH2O, respectively, were synthesized through ion exchange with a higher yield (~90%) than the conventional organic route (~70%). Wells-Dawson heteropolyacids are obtained when the corresponding ammonium salt [(NH4)6P2W18O62.13H2O and (NH4)6P2Mo18O62.12H2O] is kept in contact with an acid resin [about (1:0.8) salt:resin weight ratio] up to 3 days. The use of an organic media instead of an aqueous media greatly favors the completeness of the exchange. Isopropanol chemisorption and temperature programmed surface reaction (TPSR) towards propylene allowed the determination of the number of active acid sites and the activation energy in order to compare the acid properties of HPAs with various catalytic materials. The HPAs possess a higher number of active acid sites than monolayer supported materials due to their microporous structure. Moreover, a stressed electronic influence of the oxide support (W-O-Support) and the central phosphorous atom (W-OP) on the acid strength was observed.