RE₂O₃-promoted Pt-SO₄^2-/ ZrO₂-Al₂O₃ catalyst in n-hexane hydroisomerization

Lanthanum, cerium and ytterbium nitrates used as RE oxide precursors, RE₂O₃-promoted PSZA catalysts for n-hexane hyroisomerization were prepared and RE₂O₃ promotion effects on catalytic activity and catalytic stability were investigated by N₂-adsorption, XRD, TG, FTIR, XPS and H₂-TPR. It was elucidated that the introduction of RE₂O₃ into Pt-SO ₄^2-/ZrO₂-Al₂O₃ (PSZA) increased both the surface area and the number of active sites, resulting in a higher n-hexane isomerization activity. At the same time the catalyst stability has also been markedly increased by alleviating the sulfur loss and by stabilizing ZrO₂ tetragonal crystalline structure. In addition, XPS for the spent catalysts showed during n-hexane hydroisomerization reaction a relative small amount of S⁶⁺ species was reduced to S⁴⁺, and the amount of the most active sulfate entities decided the overall amount of n-hexane transformed, their reduction being, perhaps, retarded by the RE ₂O₃ addition to PSZA. The promotion effects of RE oxides addition decreased in the order: La₂O₃ > Yb ₂O₃ > Ce₂O₃.