Unraveling the Homologation Reaction Sequence of the Zeolite‐Catalyzed Ethanol‐to‐Hydrocarbons Process

Although industrialized, the mechanism for catalytic
upgrading of bioethanol over solid-acid catalysts (that is, the
ethanol-to-hydrocarbons (ETH) reaction) has not yet been
fully resolved. Moreover, mechanistic understanding of the
ETH reaction relies heavily on its well-known “sister-reaction”
the methanol-to-hydrocarbons (MTH) process. However, the
MTH process possesses a C1
-entity reactant and cannot,
therefore, shed any light on the homologation reaction
sequence. The reaction and deactivation mechanism of the
zeolite H-ZSM-5-catalyzed ETH process was elucidated using
a combination of complementary solid-state NMR and operando UV/Vis diffuse reflectance spectroscopy, coupled with online mass spectrometry. This approach establishes the existence
of a homologation reaction sequence through analysis of the
pattern of the identified reactive and deactivated species.
Furthermore, and in contrast to the MTH process, the
deficiency of any olefinic-hydrocarbon pool species (that is,
the olefin cycle) during the ETH process is also noted.