Acid Property of Sulfur-Promoted Zirconium Oxide on Silica as Solid Superacid

An SO3-promoted ZrO2/SiO2 was found to be a solid superacid that had the acid strength of higher than H0=−13.16, regardless of the amount of ZrO2 loaded. The sample of 3.5 mmol g−1 of ZrO2 loaded on SiO2, which was the highest amount of loading tested here, showed the highest acid strength of H0≤−14.52. A tetragonal form of ZrO2 was found to grow extensively when the amount of ZrO2 loaded became larger. Thus, it was concluded that the higher acid strength of thus prepared catalyst could be obtained after the crystal growth of supported oxide.