Isomerization of n-hexane over sulfated zirconia: Influence of hydrogen and platinum

Isomerization of n-hexane (1-5 bar) is studied over sulfated zirconia at 42 3 K and 50 bar, under 5-45 bar hydrogen. The sulfated zirconia is crystalli zed at 923 K, then loaded with 0.025-0.8 wt% platinum. The isomerization ra te first increases with hydrogen pressure, reaches a maximum, and finally d ecreases slowly. At a given platinum content, the position of the maximum i ncreases with hexane pressure. The shape of the activity curves versus hydr ogen partial pressure depends strongly on the platinum content. All the act ivity data are kinetically modeled by an acid mechanism in which the Lewis acid-base sites create carbenium ions. Activated hydrogen on platinum spill s over to form the hydride species responsible for the desorption of the is ocarbenium ions. The three parameters of the rate equation reflect the numb er of sites, the acid strength, and the efficiency of platinum. In the seri es of catalysts examined, the acidity is constant while the platinum effici ency increases with loading and reaches an upper limit at 0.15% platinum lo ading. (C) zool Academic Press.