Hydroisomerization of benzene-containing gasoline fractions on a Pt/SO ²⁻₄ -ZrO₂-Al₂O₃ catalyst: II. Effect of chemical composition on acidic and hydrogenating and the occurrence of model isomerization reactions

Abstract

The acidic and hydrogenating of Pt/SO ²⁻₄ -ZrO₂-Al₂O₃ samples containing from 18.8 to 67.8 wt % Al₂O₃ as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of n-heptane decreased with the concentration of Al₂O₃; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al₂O₃. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached on the above catalyst sample. This can be explained by lower concentrations of Lewis and Brønsted acid sites in the Pt/SO ²⁻₄ -ZrO₂-Al₂O₃ system, as compared with those in Pt/SO ²⁻₄ -ZrO₂. The experimental results allowed us to make a preliminary conclusion that the Pt/SO ²⁻₄ -ZrO₂-Al₂O₃ catalyst whose support contains 67.8 wt % Al₂O₃ is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically favorable process temperature range of 250–300°C.