New insight into the enhanced catalytic performance of ZnPt/HZSM-5 catalysts for direct dehydrogenation of propane to propylene

Catalysts comprising zinc and platinum supported on high-silica HZSM-5 (HZ) were prepared for catalyzing the direct dehydrogenation of propane to propylene (PDH). The catalysts were characterized by a series of techniques, including XRD, N-2 sorption, TEM, H-2-TPR, NH3-TPD, XPS and TGA. The optimal 10Zn0.1Pt/HZ catalyst (consisting of 1000 ppm Pt and 10 wt% Zn) shows a high propylene yield (about 46%) and extraordinary dehydrogenation stability over 65 h at 525 degrees C without any regeneration procedure or H-2 as auxiliary gas. It is revealed that this catalyst has two kinds of active centers which work corporately: (i) Lewis acidic sites created by framework Zn species and (ii) small-sized PtZn particles. In addition, the stable state of the active species and strong carbon resistance of 10Zn0.1Pt/HZ related to the interaction effect between Pt and Zn are confirmed, accounting for the admirable reaction stability of PDH. This catalyst contains much more Zn and less Pt than previously reported PtZn-based dehydrogenation catalysts, breaking the traditional understanding about Pt-Zn catalysts and opening a wide avenue for the design of stable dehydrogenation catalysts.