Location and structure of coke generated over Pt–Sn/Al2O3 in propane dehydrogenation

Pt and Pt–Sn/alumina catalysts were prepared by either an incipient wetness impregnation or co-impregnation method, and their deactivation behavior, coke structure and coke location in propane dehydrogenation were investigated by XRD, XPS, TPO and reaction tests. The XRD and XPS measurements confirmed that coke structure over all spent catalysts was pregraphite-like carbon, which presents at 2θ = 25° in XRD patterns and binding energy = 283.9 eV in XPS spectra. In the TPO results, along with Sn contents, oxidation peak of coke was shifted to a higher temperature, which can be interpreted that coke formed during the reaction was mainly located on the support in the case of Pt–Sn/alumina because coke generated on metal surfaces was readily transferred to the support in the presence of Sn. This would be responsible for high tolerance of Pt–Sn/Al2O3 to catalyst deactivation.