Durability improvements of H-ZSM-5 zeolite for ethanol conversion after treatment with chelating agents

• Durability of ZSM-5 in ETH process can be increased by washing with chelating agents.
• Not the sample's bulk properties but its texture elements are the crux of the matter.
• Extra-framework species in outer layers of the zeolite are crucial to its durability.

An H-ZSM-5 zeolite (Si/Al = 12) was treated with solutions of tartaric acid, citric acid and EDTA. The impact of this treatment on the durability in the conversion of ethanol was investigated and correlated with the extraction of small amounts of aluminium. M06-L/6-31G(d) was applied as level of theory for the quantum chemical part of this work. These investigations showed that all EFSPE can be regarded as solvable and hence also as removable. By solid state characterisations (NMR, IR, XRD) no changes in the bulk properties were observed, although catalytic testings of the treated samples showed significant durability improvements. This ostensible contradiction can be explained by a changed ethene supply to the hydrocarbon pool after the removal of EFSPE acting as active sites which catalyse only dehydration reactions.

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