Synthesis and Characterization of Sulfated Titania Solid Acid Catalysts

Sulfated titania catalysts were prepared by precipitation of titanic acid from titanium tetrachloride using aqueous ammonia, followed by impregnation with sulfuric acid. The sulfate concentrations in the catalysts were in the range 5−15 wt %. These sulfated catalysts were calcined at temperatures in the range 450−650 °C. The characteristics of these sulfated titania catalysts were examined using BET, SEM, powder XRD, ICP−AES elemental analysis, FT-IR, TPD of NH3, TPD of pyridine, and 1H MAS solid state NMR measurements. The activities of these catalysts were evaluated using n-butane isomerization studies to produce isobutane in a fixed-bed microreactor operated at 1 atm, 100−250 °C, and a space velocity (WHSV) of 5−15 h-1. The n-butane conversion and isobutane selectivity were at a maximum with a sulfate concentration of 12.5 wt % and a reaction temperature of 150 °C. Results showed a linear relationship between the acidity of the catalysts and their isomerization activity. The isomerization activity of sulfated titania catalysts were compared with those of other solid acid catalysts such as sulfated zirconia and Pt−HZSM-5 catalysts. This study indicated that isobutane selectivity as well as the acidity increased in the order sulfated zirconia ≫ sulfated titania > Pt−HZSM-5.