Conversion of methanol to hydrocarbons over conventional and mesoporous H-ZSM-5 and H-Ga-MFI: Major differences in deactivation behavior

Methanol has been converted to hydrocarbons over conventional and mesoporous H-ZSM-5 and H-Ga-MFI. The gallium based zeotypes are analogous to H-ZSM-5, but the Brønsted acidity is introduced by framework incorporation of gallium rather than aluminum, which leads to lower intrinsic acid strength. In the methanol-to-hydrocarbons (MTH) process, H-ZSM-5 is subjected to coke formation leading to catalyst deactivation. Here we show that when the gallium containing zeotypes are employed in the MTH process, only insignificant amounts of coke are present in the deactivated catalysts, indicating distinct differences in deactivation mechanisms of the two different catalysts. This is investigated further through FT-IR measurements as well as catalytic experiments employing regenerated and steamed catalysts. From this it is concluded that the H-Ga-MFI is subjected to irreversible deactivation by steaming (hydrolysis) of the GaO bonds in the zeolite structure rather than coke deposition.

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► Methanol is converted over conventional and mesoporous H-ZSM-5 and H-Ga-MFI.
► The rate of coke formation during conversion of methanol is very low for H-Ga-MFI.
► The H-ZSM-5 based zeolites deactivate through coke deposition.
► The gallium based zeotypes deactivate through steaming rather than coke deposition.