Calcium Salts of Tungstophoric Acid Supported on Silica as Novel Catalysts for Tetrahydrofuran Polymerization

The 12-tungstophoric acid (HPW) and its calcium salts Cax/2H3-xPW12O4 with the calcium content in the range 0 < x < 3 supported on silica were synthesized, and their catalytic properties were also studied in the polymerization of tetrahydrofuran under mild conditions. These catalysts were characterized by isothermal nitrogen adsorption/desorption, infrared spectroscopy, n-butylamine electrometric titration, and thermal analysis. The calcium salts presented strong acidity and high catalytic performance. When x = 2.0, the supported calcium salt CaHPW12O40/SiO2 calcined at 300 A degrees C gave the highest catalytic activity. However, a poor catalytic activity was only obtained over the Ca1.5PW12O40/SiO2 catalyst substituting all protons of phosphotungstic acid, which was due to its weakest acidity. The CaHPW12O40/SiO2 sample showed better reusability than normal HPW/SiO2 catalyst, and reacted as a recyclable and effective catalyst for tetrahydrofuran polymerization.