Influence of sulfation and structure of zirconia on catalytic isomerization of n-hexane

Two series of sulfated zirconia have been prepared by immersing amorphous or crystalline zirconia in an H2SO4 solution (0.25-2.5 M). They were compared with a commercial sulfated zirconium hydroxide. Activation temperature was varied between 300 and 725 degrees C. Sulfate density varied so that the mean surface area of an individual sulfate ranged from 0.14 to 0.54 nm(2). Three limiting sulfate states are evidenced and characterized by TPR-MS. Catalysts are tested for isomerization of n-hexane at 150 degrees C and 3 MPa. Factors influencing the activity are discussed. The data show that a highly active and selective catalyst for producing hexane isomers requires tetragonal zirconia with a sulfate occupancy of about 0.40 nm(2). Preparation parameters must therefore be adapted to match these constraints.