Effects of metal modification on the performance of Pt/β-zeolite catalysts in the oxidation of HC, CO and SO₂ in diesel exhaust

Pt/β-zeolite catalysts were modified with Ce, Cr, Mo and Cu by impregnation method and characterized by nitrogen sorption, XRD, H₂-TPR, NH₃-TPD and XPS; the effects of metal modification on the textural properties, skeletal structure, surface acidity as well as the catalytic performance in the oxidation of SO₂, HC and CO in the simulated diesel exhaust gas were investigated. The results indicate that metal modification has little influence on the textural properties and skeletal structure of the Pt/β-zeolite catalyst, whereas the addition of Cu, Cr and Mo can change the acid strength and has a stronger inhibition effect on the oxidation of SO₂. Especially, the Cu-modified Pt/β-zeolite catalyst exhibits the best ability to inhibit the oxidation of SO₂; the SO₂ conversions over Cu modified catalyst under 350 and 450 ℃ are decreased by 70.4% and 70.2%, respectively, in comparison with those over the unmodified Pt/β-zeolite catalyst. However, because of the interaction between metal and Pt species, Pt species becomes more difficult to reduce over the metal modified Pt/β-zeolite catalysts, which may lead to a decrease of their catalytic activity in the oxidation of HC and CO.