Dehydrogenation of propane over Ga and Cr modified, "fresh" and steamed, MFI-type zeolites

In this work we synthesized MFI type zeolites with chromium and gallium. Hydrothermal synthesis was applied using, either aluminum with gallium or chromium sources in 1:1 mole ratios, or impregnation of H-ZSM-5 with the desired metal. The "as synthesized" samples were characterized by XRD, Chemical analysis, SEM-EDS, SSA, ammonia-TPD and subjected to severe steaming, in order to suppress their acidity and consequently decrease the oligomerization capability of the formed catalysts. The catalytic activity of the zeolite samples in propane dehydrogenation was investigated using a fixed-bed continuous-flow glass reactor. The catalytic test results revealed that propylene yield and selectivity over the steamed catalysts increased remarkably (e.g. propylene yield ∼11% with selectivity of ∼45%, for H-[Ga/Al]ZSM-5), as a consequence of the suppression of their acidity and therefore of the dramatic decrease of their oligomerization capability. The above results suggest that Cr- and Ga-modified steamed zeolites are promising catalysts for the dehydrogenation of propane to propylene.