| Abstract |
Two series of supports and catalysts were prepared exchanging beta zeolite with alkali or alkali-earth cations. The influence of the exchanged cation (M = Na, K, Rb, Cs, Mg, Pa) on the catalytic behaviour of Pt/M beta catalyst in n-heptane reactions was studied. Platinum was introduced into the supports by ionic exchange. The supports and Pt catalysts were chemical and structurally characterized by different techniques (AA, ICP, XRD, ammonia TPD, cyclohexane adsorption, H-2-TPR, etc.). The acidity and adsorption capacity decrease as the cation size increases. In the case of alkali cations, the catalytic activity of the support is negligible. However, greater acidity and stronger acid sites present on alkali-earth supports provide a high catalytic activity. The deactivation rate and the amount of coke determined by TG are related. The nature of the coke was discussed on the basis of DSC results obtained during the coke burning. Coke deposited on alkali and alkali-earth M beta zeolite during the n-heptane transformation becomes progressively more stable as the support acidity and the time on stream increase. The localization of Pt particles and their proximity to the acid sites influence the coke composition and its removal. The regeneration of Pt/K beta was performed and the results showed that the catalyst fully recovers its catalytic behaviour. (C) 1998 Academic Press. |
