Hydroisomerization of n-butane over sulfated zirconia catalysts promoted by alumina and platinum

The isomerization of n-butane over Pt-promoted/Al2O3-promoted sulfated zirconia (Pt/SZA) catalyst in comparison with SZA was studied in the presence of H-2 at 250degreesC. Catalysts prepared using IN H2SO4 are slightly more active than those prepared using 2N H2SO4. The optimum calcination temperature for Pt/SZA was found to be 650degreesC, same as for SZA catalyst. The presence of platinum improves the catalytic stability and isomerization selectivity of SZA catalyst, particularly at low H-2/n-butane ratio. Comparing the maximum activity displayed by both catalysts, Pt/SZA is more active than SZA for n-butane isomerization, especially at the steady state. Pre-treating the Pt/SZA catalyst in H-2 at 350 degreesC before the reaction results in a significant loss in activity. The mechanical mixture of Pt/Al2O3 and SZA exhibits much higher activity than Pt/SZA catalyst, probably due to a change of reaction mechanism from monofunctional over the latter catalyst to bifunctional over the former. The initiation step of n-butane isomerization over SZA catalyst is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.