Ethane dehydrogenation over Zn-ZSM-5 zeolites synthesized via vapor deposition

Catalytic dehydrogenation of ethane to produce ethylene is an appealing pathway for the utilization and valorisation of light alkanes in shale gas. In this context, zinc deposited in zeolites are promising candidates for the selective dehydrogenation of ethane. In the present work, Zn-ZSM-5 catalysts were prepared via incipient wetness impregnation (IWI), aqueous ion exchange (IE), and chemical vapor deposition (VD) methods. Characterizations via XRD, XPS, UV-Vis, H2-TPR, FTIR, and Py-FTIR reveal that different preparation methods influenced the speciation of zinc. IE and VD methods allowed to prepare zinc cations exchanged with Brønsted acid sites (BAS), while zinc oxides were found to be dominant in IWI sample at a high Zn content of 10 wt%. VD approach enabled zinc cation loading up to 9.2 wt%, facilitating the formation of bridged zinc cations [Zn-O-Zn]2+. These differences in speciation, in turn, reflect on the catalytic activity, in which Zn-Z5-VD catalyst exhibited the highest ethylene selectivity of 82 mol% and ethylene space time yield (STY) of 4.0 mmol gcat-1 h-1 at 500oC and gas hourly space velocity (GHSV) of 4000 ml­­C2H6 gcat-1 h-1. This remarkable performance was attributed to the formation of [Zn-O-Zn]2+ species behaving as strong Lewis acid sites (LAS) that were very active for dehydrogenation via strong adsorption of ethane, as determined by in situ DRIFTS.