Preparation of ZrO₂–SiO₂ mixed oxide by combination of sol–gel and alcohol-aqueous heating method and its application in tetrahydrofuran polymerization

Without using any acid or base catalyst, complexing agent or zirconium alkoxides, ZrO₂–SiO₂ mixed oxide with the ZrO₂ content of 50 mol% was prepared by combination of sol–gel and alcohol-aqueous heating method using zirconyl nitrate and tetraethoxysilane as starting materials. The structural and surface acidic properties were characterized by FT-IR, XRD, NH₃-TPD and pyridine adsorption FTIR. Compared with another mixed oxide with the same ZrO₂ content prepared by mechanical grinding, the obtained ZrO₂–SiO₂ mixed oxide was homogeneously mixed in molecular level. The existed Zr–O–Si hetero-linkages strongly retarded the ZrO₂ particle growth. The obtained mixed oxide maintained amorphous phase until it was calcined at 1,173 K for 3 h when crystallization of tetragonal zirconia took place. NH₃-TPD and pyridine adsorption FTIR showed that both Brønsted and Lewis acidity were largely developed in the mixed oxide and most of the acidic sites belonged to the medium acidity. Because of the existence of abundant medium acidity, the mixed oxide showed catalytic activity for tetrahydrofuran polymerization. Furthermore, the produced poly tetramethylene ether glycol had moderate average molecular weight around 2,000. Neither the pure oxides nor the mixed oxide prepared by the mechanical grinding presented catalytic activity for this reaction.