Heteropolyacid Catalysts for Hydroisomerization of n-Hexane: Effects of Alkali Salt Modification

12-Tungstophosphoric acid, H3PW12O40, and a series of its acid alkali salts associated with silica-supported platinum have been used as catalysts in the hydroisomerization of n-hexane and compared with platinum-supported, appropriately dealuminated mordenite. High selectivity toward isomerization was observed with both the heteropolyacid (HPA)-type catalysts and the mordenite at elevated conversions. The acid sites of the heteropolyacids/salts exhibited an efficiency higher than that of mordenite, in line with the higher acid strength of the former sites. Yet, despite their higher acid strength, heteropolyacids/salts showed a lower selectivity toward dimethylbutanes than mordenite. In addition, heteropolyacids, though more active than mordenite at low temperature, appeared to be only poor monofunctional isomerization catalysts.