Synthesis and study of superacid ZrO2-SiO2-Al2O3 mixed oxide

Strongly acidic ZrO2-SiO2-Al2O3 mixed oxide with different Zr:Si:Al ratios have been synthesized by sol-gel method. It was found that superacid (H-0 = -14.52) sites are formed at 12 <= Zr4+ <= 39, 48 <= Si4+ <= 72, 3 <= Al3+ <= 31 at.%. According to the infrared spectra of adsorbed pyridine and acetonitrile-D-3, acidic B-and strong L-sites are present on ZrO2-SiO2-Al2O3 surface. Observed high-energy shift of Zr 3d(5/2) peak in the X-ray photoelectron spectrum and low-field shift of Si-29 nuclear magnetic resonance signal of superacid Zr35Si53Al12 oxide indicate that the electron density transfers from zirconium to silicon atom. The generation of superacidity in ZrO2-SiO2-Al2O3 matrix could be explained by formation of coordinatively unsaturated Zr4+ ions which are strong L-sites. It was shown that superacid ZrO2-SiO2-Al2O3 efficiently catalyzes polymerization of tetrahydrofuran in the presence of acetic anhydride at 40 degrees C with 68% yield of polytetramethyleneoxide acetate.