New catalyst of SO42-/Al2O3-ZrO2 for n-butane isomerization

The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H-2 and at high temperature in the presence of H2 was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250 degrees C and in the presence of H-2 significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al2O3 keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect of Al is different from that of the transition metals. Microcalorimetric measurements of NH3 adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement in the number of acid sites effective for the isomerization reaction.