Investigation of factors influencing catalytic activity for n-butane isomerization in the presence of hydrogen on Al-promoted sulfated zirconia

Two series of Al-promoted sulfated zirconia with 3 mol% Al2O3 content were prepared. In one case, zirconium-aluminum hydroxide has been aged at room temperature; in the other case, zirconium-aluminum hydroxide has been synthesized at 373 K under hydrothermal condition. For the two series of samples, the influence of the synthesis parameters such as ageing time, the amount of ammonia added, and zirconium concentration on catalytic activity for n-butane isomerization in the presence of hydrogen were investigated. Moreover, Al-promoted sulfated zirconia with a high surface area (174 m2/g) can be obtained by properly adjusting synthesis parameters under hydrothermal condition at 373 K. The catalytic data showed that this material had similar catalytic activity to a conventional Al-promoted sulfated zirconia with a low surface area (98 m2/g). The characterization of the samples revealed that the catalytic activity was directly correlated with sulfur content rather than surface area, sulfate density and the total number of Brønsted acid sites. The synthesis of the precursors of hydroxides before sulfation is a crucial step for catalytic activity of the samples in n-butane isomerization.