Pt-Sn alloy phases and coke mobility over Pt-Sn/Al2O3 and Pt-Sn/ZnAl2O4 catalysts for propane dehydrogenation

Propane dehydrogenation on Pt-Sn/Al2O3 and Pt-Sn/ZnAl2O4 was performed, and the Pt-Sn/ZnAl2O4 catalyst showed a stronger tolerance for catalytic deactivation than the Pt-Sn/Al2O3 catalyst. In this study, we propose that the high catalytic stability of Pt-Sn/ZnAl2O4 originates from the relatively faster coke mobility from the metal surface to the support, which was proven by XPS measurement. XRD and HRTEM associated with EDX demonstrated that Pt-Sn alloy phases over the catalysts were transformed during the reaction and that the bimetallic phase transition was different according to the supports. Both PtSn and Pt3Sn alloys were formed on the reduced Pt-Sn/Al2O3, while only the PtSn alloy was observed on the reduced Pt-Sn/ZnAl2O4. The Pt3Sn phase was dominant over the spent Pt-Sn/Al2O3, whereas the PtSn phase remained unchanged over the spent Pt-Sn/ZnAl2O4 after reactions for 160 and 240 min. The different bimetallic alloy formations and phase transitions in the Pt-Sn catalysts cause different coke mobilities. (C) 2011 Elsevier B.V. All rights reserved.