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

摘要

The isomerization of n-butane over Pt-promoted/Al_2O_3-promoted sulfated zirconia (Pt/SZA) catalyst in comparison with SZA was studied in the presence of H_2 at 250 deg C. Catalysts prepared using 1N H_2SO_4 are slightly more active than those prepared using 2NH_2SO_4. The optimum calcination temperature for Pt/SZA was found to be 650 deg C, same as for SZA catalyst. The presence of platinum improves the catalytic stability and isomerizatio selectivity of SZA catalyst, particularly at low H_2-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 deg C before the reaction results in a significant loss in activity. The mechanical mixture of Pt/Al_2O_3 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.