Analysis of coke deposition and study of the variables of regeneration and rejuvenation of naphtha reforming trimetallic catalysts

The deactivation, by coke deposition and sintering, and the regeneration of the metal function of PtReSn/Al2O3–Cl and PtReGe/Al2O3–Cl catalysts were studied. The variables affecting the rejuvenation of the metal function (oxychlorination at 480 °C with 300, 530 and 900 ppm, stabilization at 520 °C) and the coke burning-off (400–500 °C, 0.5, 2, 6 or 12 h) were assessed. The analysis of the carbon deposits and of the final state of the metal and acid functions were performed by means of temperature programmed oxidation, temperature programmed reduction and temperature programmed pyridine desorption (TPO, TPR and TPD-Py) respectively. The degrees of deactivation and activity recovery of the metal function were measured by means of the cyclohexane dehydrogenation and cyclopentane hydrogenolysis reactions. The deactivation or activity recovery of the acid function assessed with the n-pentane isomerization reaction. It was found that the PtReSn catalysts were more stable than the PtReGe ones. This was due to the lower amount of coke deposited on the surface of PtReSn. It was found that when the catalysts were oxidized with an oxygen stream more than 6 h were needed to eliminate the coke at 400 °C while at 500 °C the coke was eliminated in 30 min. Regeneration produced a segregation of the metal phase on both kinds of catalysts. Metal particle sintering at 650 °C modified the metal function severely and Pt was segregated from the other components. All the rejuvenation treatments (Cl, air and high temperature) were unable to restore the original state of the metal function.