Yasutaka Nagai, Hirofumi Shinjoh, Koji Yokota

A highly selective oxidation performance, which has a higher oxidation activity for hydrocarbons than that for SO₂, is required for diesel oxidation catalysts. We examined the oxidation reaction of n-C₆H₁₄ and SO₂ over two types of Pt/ZrO₂ catalysts with low (8 m² / g) and high (75 m²/g) surface areas of the ZrO₂ supports (referred to as ZrO₂-8 and ZrO₂-75, respectively). The Pt/ZrO₂-75 exhibited a desirably higher selectivity for the complete oxidation of n-C₆H₁₄ than that of SO₂, as compared with the Pt/ZrO₂-8. In order to clarify the cause of this selective oxidation, we investigated the Arrhenius parameter for these oxidation reactions and characterized these catalysts using XPS, XRD, TEM, IR and CO₂-TPD methods. The amount of Pt⁰ (metal) in the Pt/ZrO₂-75 was significantly lower than that in Pt/ZrO₂-8, because the high basicity of the ZrO₂-75 support stabilized the high oxidation state of Pt such as Pt²⁺ and Pt⁴⁺. It was concluded that the difference in the number of Pt⁰ sites as catalytic active sites causes the apparent selectivity to change due to the much slower reaction rate for the SO₂ oxidation than that for the n-C₆H₁₄ oxidation.