On the remarkable resistance to coke formation of nanometer-sized and hierarchical MFI zeolites during ethanol to hydrocarbons transformation

• Hierarchization impacts coking and decoking of MFI catalysts in the transformation of Ethanol to hydrocarbons.
• Nanometer-sized are superior to hierarchical micron-sized MFI zeolites to prevent coke.
• The superior performances of nanometer-sized zeolites are related to shorter diffusion path lengths
• Caustic leaching produces more efficient catalysts than fluoride leaching.

The impact of the textural properties of H-ZSM-5 zeolites in the conversion of ethanol to hydrocarbons at 623 K and under 3.0 MPa pressure is investigated. We highlight that the lifetime of the catalysts is not correlated to the coking rate but to the number of pore mouths. The addition of macropores (fluoride leaching) or mesopores (alkaline leaching) to micron-sized zeolites is a simple approach to increase the number of pore mouths and reduce the diffusion path length of molecules in the micropores. However, the most efficient way is to reduce the zeolite crystal size to nanometers. The longest catalyst lifetime (>>100 h) is obtained with a hierarchical nanometer-sized zeolite even though most of its acid sites are poisoned. The important impact of the nature of coke on the catalysts regeneration is also highlighted.

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