Abstract
The additive effect on the low temperature propane combustion over the supported platinum catalyst was investigated by using Pt/Al 2O 3 with a series of additives. The catalytic activity of platinum catalyst drastically varied with the kind of additives, and increased with the increase in the electronegativity of additives. The additive with large electronegativity enhanced the catalytic activity compared with the original Pt/Al 2O 3 and vice versa. The additive effect on the oxidation state of platinum was investigated by Pt L II- and L III-edge XANES. In the oxidizing atmosphere, the oxidation state of platinum varied with the electronegativity of additives to a more or less oxidized state compared with original Pt/Al 2O 3: the oxidation of platinum was more depressed by the additives with larger electronegativity, indicating that the oxidation-resistance of platinum is more enhanced with the increase in the electronegativity of additives. Although the electron deficiency of platinum increases with the increase in electronegativity of the additives in the reducing atmosphere, the additive effect in the oxidizing atmosphere is entirely different from that in the reducing one. The relation between the catalytic activity of platinum and its oxidation state indicates that the variation in the catalytic activity comes from the variation in the oxidation state, and that the additives affect the catalytic activity through the control of oxidation state of platinum. This additive effect is similar to the support effect on platinum catalyst for propane combustion found in the previous studies; platinum on more acidic support materials has higher oxidation-resistance, and the catalytic activity of supported platinum can be improved through the control of the oxidation state of platinum by support materials. These results clearly reveal that the electrophilic/electrophobic properties of the support materials and additives is one of the key factors for the control of the activity of platinum catalyst used under the oxidizing atmosphere.
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