Coke formation on dehydrogenation catalysts

Abstract

The objective of this research was to study the deactivation in propane dehydrogenation reaction of prepared catalysts and to characterize the coke deposited on these catalysts. The prepared catalysts were (0.3 wt.%)Pt/Al2O3, (0.3 wt.%)Pt-(0.3 wt.%)Sn/Al2O3, (0.3 wt.%)Pt-(0.3 wt.%)Re/Al2O3, (0.3 wt.%)Pt-(0.3 wt.%)Sn-(0.6 wt.%)Li/Al2O3,and 0.3 wt.%)Pt-(0.3 wt.%)Re-(0.6 wt.%)Li/Al2O3. Comparison to the base Pt/A2O3 catalyst, the Pt-Sn/Al2O3 and Pt-Sn-Li/Al2O3 have higher initial propane conversion. On the contrary, Pt-Re/Al2O3 and Pt-Re-Li/Al2O3 have lower initial propane conversion than the Pt/A2O3 catalyst. An addition of tin to the base Pt/Al2O3 catalyst enhances the propylene selectivity. And addition of rhenium to Pt/Al2O3 promoted the methane, ethane, and ethylene selectivities of catalysts. Comparison of irreversible coke responsible for long term deactivation of metal active sites, was done among the set of Pt/Al2O3, Pt-Sn/Al2O3, and Pt-Sn-Li/Al2O3 catalysts. The amounts deposits could be arranged in the decreasing order as : Pt-Sn/Al2O3 > Pt/Al2O3 >Pt-Sn-Li /Al2O3. The amounts or irreversible coke deposited on the metal active sites of the catalyst was higher for the catalyst that had the higher amounts of total irreversible coke. The addition of lithium decreased the formation of the irreversible coke.