The discovery of the dual aromatic- and olefin-based
catalytic
cycles in methanol-to-hydrocarbons (MTH) catalysis on acid zeolites
has given a new context for rationalizing structure–function
relationships for this complex chemistry. This perspective examines
six major chemistries involved in the hydrocarbon pool mechanism for
MTHolefin methylation, olefin cracking, hydrogen transfer,
cyclization, aromatic methylation, and aromatic dealkylationwith
a focus on what is known about the rate and mechanism of these chemistries.
The current mechanistic understanding of MTH limits structure–function
relationships to the effect of the zeolite framework on the identity
of the hydrocarbon pool and the resulting product selectivity. We
emphasize the need for assessing the consequences of zeolite structure
in MTH in terms of experimentally measured rates and activation barriers
for individual reaction steps and in terms of speciation preferences
within the dual olefin- and aromatic-catalytic cycles to alter their
relative propagation. In the absence of individual reaction rates,
we propose using ethene/isobutane selectivity as a measure to describe
the relative rates of propagation for the aromatic- and olefin-based
cycles.
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