Preparation and catalytic properties of supported heteropolyacid salts

Heteropoly compounds are receiving increasing interest as environmentally compatible solid acid catalysts. Partial Cs⁺ exchange into 12-tungstophosphoric acid converts the water soluble, low surface area (< 5 m² g⁻¹) parent acid into submicron water-insoluble Brønsted acids with surface areas exceeding 100 m² g⁻¹. The insolubility of the Cs acid salt makes preparation of large particle supported catalysts by conventional impregnation procedures impractical, although applications in packed bed or slurry reactors require millimeter-sized pellets to avoid pressure drop or filtration problems. Here, we report on a new but simple technique that produces an eggwhite distribution of active Cs-acid salt of 12-tungstophosphoric acid within a large silica extrudate by carrying out a reaction deposition directly inside the extrudate. We examine these catalysts in aromatic alkylation reactions.