Determination of irreversible coke deposition of platinum active site of propane dehydrogenation catalyst

Abstract

To study the synergisticeffect and Nature of coke deposition in propane dehydrogenationreaction oF prepared catalysts. The catalysts were Pt/Al(,2)O(,3)Pt-Sn/Al(,2)O(,3), Pt-Sn-Li/Al(,2)O(,3) and Pt-Sn-Na/Al(,2)O(,3). The increase of Pt loading enhances catalyst performanceand increases total coke deposits on the catalyst. Presence oftin increases catalyst performance, and total coke deposits onthe catalyst but a larger vacant site of Pt on metal active siteremains free; this is explained by a drain-off effect. Presenceof alkali increases catalyst performance, reduces coke depositson the catalyst and metal active site; this is caused by hydrogenspill over. At higher hydrogen-to-hydrocarbon ratios, the catalystperformance is decreased and coke on the metal site is decreasedalso. As time on sream reached the steady state, the cokesdeposited on metal sites are constant. The possible functions of promoters are proposed; they aretextural. structural and alloy functions. The model of reversiblecoke and irreversible coke formation is composed of series offragmentation, dehydrogenation reaction and migration of cokeprecursor, reversible coke and irreversible coke. Finally, themodel for regeneration which suggests that reversible coke on ametal active site is removed all by diluted oxygen at 250 degreeC and irreversible coke on a metal active site is removed all bydiluted oxygen at 500 degree C is proposed.