Effect of Size and Extent of Sulfation of Bulk and Silica-Supported ZrO2 on Catalytic Activity in Gas- and Liquid-Phase Reactions

Article abstract of DOI:10.1021/jp030436b

Sulfated zirconia was prepared according to three different procedures, i.e., conventional impregnation with sulfuric acid and calcinations of two zirconia, reaction of zirconium tetrachloride with sulfuric acid giving bulk anhydrous zirconium sulfate, and deposition-precipitation of highly dispersed zirconia on silica and subsequent reaction with either H₂S or O₂, or SO₂ and O₂, or SO₃. For the thermal pretreatment of sulfated zirconia, it was important that the constituents of sulfuric acid show a considerable vapor pressure at significantly lower temperatures than the temperatures at which zirconium sulfate decomposes. The rate of transport of water out of a catalyst batch being thermally pretreated is decisive for the final activity of the catalyst. The catalysts were employed in the gas-phase trans-alkylation of benzene and diethylbenzene to ethylbenzene at 473 and 673 K and in the solvent-free, liquid-phase hydroxyacyloxy-addition of acetic acid to camphene to isobornyl acetate at 338 K. The volatility of the components of the active species also affected the activity in gas-phase reactions. The catalytic activity of sulfated zirconia catalysts originated from supported sulfuric acid containing water. The deficiencies of water-diluted sulfuric acid, volatility and solubility in liquid, had to be considered in the technical utilization of sulfated zirconia catalysts.