Effects of Metal Loading on the Superacidity and Catalytic Properties of SO₄^2-/ZrO₂

The effects of different pretreatment and reaction atmospheres and metal loading on the catalytic properties of SO₄^2-/ZrO₂ for pentane isomerization reaction were studied. The initial activity of SO₄^2-/ZrO₂ in N₂ is quite high, but the catalyst deactivates quickly. In H₂ atmosphere the activity of SO₄^2-/ZrO₂ catalyst is markedly lowered. Supporting Pt on SO₄^2-/ZrO₂ improves the activity, selectivity and stability of the catalyst significantly, but Ni loading deteriorates the catalyst. IR spectroscopic studies of the catalysts revealed that the SO₄^2- on the surface of ZrO₂ may be partially reduced by H₂, and in result the amount of superacidic sites is diminished. Pt loading inhibits the reduction of SO₄^2- by H₂, so more superacidic sites are retained on the surface of the catalyst. In the same time some new strong Lewis and Bronsted acid sites are formed on Pt/ SO₄^2-/ ZrO₂. On the contrary the amount of superacidic sites on Ni/SO₄^2-/ZrO₂ is even less than that of SO₄^2-/ ZrO₂. The behavior of the various catalysts for pentane isomerization reaction is elucidated satisfactorily by correlating the IR spectroscopic results with the reaction data.