Coke combustion kinetics of spent Pt-Sn/Al2O3 catalysts in propane dehydrogenation

The kinetics of coke combustion was investigated by using a thermogravimetric analyzer (TGA) of coked catalysts which was used for propane dehydrogenation to determine the activation energy. Apart from the Pt/Al2O3 catalyst, four different Pt-Sn/Al2O3 catalysts were prepared by varying the Pt/Sn ratio from 3: 0.5 to 3: 3 by weight. The catalytic activity was measured by propane dehydrogenation at 620 °C. The reactant mixture consisting of C3H8 (30 ml/min) and H2 (30 ml/min) was fed into the reactor for 5 h. A thermogravimetric analyzer in the presence of air was used to determine the amount of coke deposited and calculate the kinetic parameters for coke combustion. Three non-isothermal models (Friedman, Flynn-Wall-Ozawa (FWO), and Kissinger-Akahira-Sunose) were used to determine the activation energy and the best model to fit the experimental data. The FWO model provided the best fit for 3Pt/Al2O3 and 3Pt-0.5Sn/Al2O3. The three models were equivalent for fitting the data for 3Pt-1Sn/Al2O3, 3Pt-2Sn/Al2O3, and 3Pt-3Sn/Al2O3. The activation energy increased with increasing Sn addition in the 3Pt/Al2O3 catalyst. Differences in the locations and the qualitative features of the cokes were suggested to interpret the results.