Al- and Ga-promoted WO₃/ZrO₂ strong solid acid catalysts and their catalytic activities in n-butane isomerization

A series of Al- and Ga-promoted tungstated zirconia strong solid acid catalysts were prepared. The effect of Al₂O₃ and Ga ₂O₃ on the structural, acidic and redox features of WO₃/ZrO₂ (WZ) has been characterized by means of X-ray powder diffraction (XRD), N₂ adsorption (BET), UV-visible diffuse reflectance spectra (UV-vis), infrared spectra (IR), NH₃ temperature-programmed desorption (NH₃-TPD) and H₂ temperature-programmed reduction (H₂-TPR). With respect to tungstated zirconia, the promoted catalysts stabilized the zirconia tetragonal phase, prevented crystalline WO₃ growth. Al or Ga addition to WZ had less effect on the strength of the acid sites, but effected reduction temperature of WZ. The isomerization of n-butane was investigated at 300°C over tungstated zirconia and promoted catalysts. The promoted catalysts improved the isomerization conversion and stability in the presence of hydrogen. The best Al and Ga loading in these catalysts is around 0.5 and 1.0%, respectively, and the optimal calcination temperature is ∼850°C. The experiment results showed that Ga was a more efficient promoter than Al. Pt addition to promoted catalysts showed great improvement on the performance of selectivity and stability.