Stable Production of Gasoline-Ranged Hydrocarbons from Dimethyl Ether over Iron-Modified ZSM-22 Zeolite

In this work, we developed metal-modified ZSM-22 zeolites for the application of converting dimethyl ether (DME) to gasoline-ranged hydrocarbons. ZSM-22 zeolite samples were modified by microwave-assisted ion exchange with nitrates of iron, nickel, copper, cobalt, and calcium. In the meantime, the acidity of the ZSM-22 zeolite was noticeably changed on the basis of the type of metal. The H-ZSM-22 zeolite showed a high selectivity to light olefins (72%). The iron-modified ZSM-22 zeolite showed a stable catalytic activity (more than 3 h) and a high olefin selectivity (54%). A strong hydrogenation behavior was observed over the nickel-modified sample, in which DME was converted to ethane, while copper, cobalt, and calcium showed a very low DME conversion combined with high selectivity to aromatics and hexane, which can be attributed to the pore blockage. Interestingly, the copper-modified sample showed a high initial selectivity to ethylene. The calcium-modified catalyst showed the lowest textural properties with very low acidity, as observed by the temperature-programmed desorption of ammonia analysis. This study will open a plethora of further research and application of the ZSM-22 zeolite and other medium-pore zeolites as catalysts for the DME to gasoline process.