On the activity and stability of platinum/alumina catalyst during multiple deactivation and regeneration

Abstract

AbstractCatalyst surface characterizations have been carried out to investigate the role of dispersion on catalyst activity and to probe the occurrence of oscillations in coking levels with cycle number generally observed during multiple deactivation and regeneration schemes. The titrations were done, cycle by cycle, at 430°C after oxidation and at the same temperature (430°C) after reduction at 500°C. Results show the usually observed trend ‐ that the dispersions after oxidation are higher than those after reduction. The average decline in dispersion from oxidation to reduction was calculated to be 39.25%. It was observed that the cycles with high toxic coke removal were characterised by high deactivation times. The deactivation times were still high even for cycles subsequent to those with low dispersion. At high dispersions the catalyst had short deactivation times, that is the small crystallites deactivate faster than large ones. The nature of reducebale coke and the efficiency of its removal is a much more determinant factor of catalyst activity than the level of metal disperision. Thus prolonged toxic coke reduction at the high temperature of 500°C, though resulting in an apparent lowering of dispersion, does not affect the quality of the catalyst. The dispersion before reduction could be retained on oxidation. Hence reduction at 500°C did not introduce sintering.