Recovery and reuse of heteropolyacid catalyst in liquid reaction medium through reversible encapsulation in Cu3(BTC)2 metal-organic framework

The solvent dependent solubility of HKUST-1 metal-organic framework (MOF) with encapsulated Keggin 12-tungstophosphoric acid (HPW@Cu-3(BTC)(2)) was exploited to liberate homogeneous heteropolyacid catalyst in a reaction medium and to recover the catalyst by encapsulation in the MOF upon addition of hexane. The application of the new Keggin type heteropolyacid catalyst recovery concept was demonstrated in the esterification of acetic acid with 1-propanol and salicylic acid with ethanol.