12-Tungstophosphoric Acid Supported on Hydrous Zirconia for Ring-open Polymerization of Tetrahydrofuran

Ring-open polymerization of tetrahydrofuran was investigated with hydrous zirconia-supported 12-tungstophosphoric acid (TPA) as catalysts. We prepared the catalysts with TPA loading (mass fraction) of 5 similar to 65 wt% by suspending hydrous zirconia in an ethanol solution of TPA, refluxing the suspension, removing the solvent by evaporation, and then calcinating the powder at 120 similar to 500 degrees C. The catalysts were characterized by ICP-AES, N(2) adsorption, XRD, FTIR spectroscopy, pyridine adsorption, and NH(3)-TPD analysis. The experiments showed that, at the moderate TPA loading (35 similar to 45 wt%) and proper calcination temperature (120 similar to 300 degrees C), TPA on support mainly existed as highly dispersed, somewhat distorted but intact Keggin species, endowing the catalysts with proper acidity and acceptable catalytic performances. A higher TPA loading gave rise to the emergence of bulk-like TPA species, whereas a lower one or a relatively higher calcination temperature resulted in the destruction of TPA Keggin units. In these circumstances, the catalyst performances declined greatly due to either the serious leaching of TPA into the product or the comparative low acidity of the catalysts. A preliminary reusability study on catalysts with 45 wt% TPA indicated that calcination at 300 degrees C could greatly enhance the stability of the catalyst.