Non-oxidative propane dehydrogenation over Pt–Zn-containing zeolites Original Research Article

Starting from the zeolites Na-ZSM-5 (MFI), Na-ZSM-11 (MEL), Na-Beta (*BEA), Na-mordenite (MOR), K-L (LTL) and Na-Y (FAU), Pt–Zn-containing catalysts with a zinc content between 0.6 and 13.4 wt.% and a platinum content of 0.5 wt.% were prepared. Zinc was introduced by impregnation or aqueous ion exchange, platinum by subsequent impregnation with H2PtCl6. The catalysts were characterized by chemical analysis (AES/ICP), X-ray diffraction (XRD), FT IR spectroscopy of adsorbed pyridine, nitrogen adsorption and temperature-programmed reduction (TPR). After the aqueous ion exchange of the zeolites with nSi/nAl-ratios ≥ 26, the zinc content in the catalysts was higher than that expected from their ion exchange capacity. This over-exchange with zinc was explained by the formation of oxidic zinc species. The Pt–Zn-containing zeolites were tested in the non-oxidative dehydrogenation of propane at 555 °C. Aromatization occurred over the 10-membered-ring zeolites Na-ZSM-5 and Na-ZSM-11, whereas propane dehydrogenation was the major reaction over the 12-membered-ring zeolites Na-Beta, Na-mordenite, K-L and Na-Y. The different procedures used for the incorporation of zinc did not significantly affect the catalytic behavior of the large-pore zeolites with lower nSi/nAl-ratios (≤ 3.4). The highest and most stable conversion levels were obtained on zeolites Beta and mordenite with nSi/nAl-ratios ≥ 8.7 and zinc contents close to 2.5 wt.%. Over the zeolite 0.5Pt/2.6Zn-Beta, a stable conversion close to the thermodynamic equilibrium for the dehydrogenation of propane to propene (XPr ≈ 29%, T = 555 °C and p = 0.1 MPa) was observed for at least 63 h time-on-stream. The propene selectivity over this zeolite was > 90%.