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Reaction Kinetics Analysis of Ethanol Dehydrogenation Catalyzed by MgO–SiO2
journal contribution
posted on 2020-05-21, 16:03 authored by Hussein
T. Abdulrazzaq, Amir Rahmani Chokanlu, Brian G. Frederick, Thomas J. SchwartzThe
Mg-catalyzed dehydrogenation of ethanol to yield acetaldehyde
is an important step in the Lebedev reaction. In this work, we prepared
a model MgO–SiO2 catalyst by impregnation of MgO
onto an SBA-15 support and used this material to study the reaction
kinetics of ethanol dehydrogenation to acetaldehyde. The rates of
acetaldehyde and ethylene production were measured for ethanol partial
pressures ranging from 0.92 to 5.25 kPa. Both rates are fractional
order at 723 K, decreasing to nearly zero-order at 648 K. Consistent
with the literature for MgO–SiO2 Lebedev catalysts,
both basic sites and Lewis acidic sites were observed on this catalyst.
The rates of both acetaldehyde and ethylene were inhibited by pyridine
but not by 2,6-ditertbutylpyridine, suggesting that both reactions
involve not only basic but also Lewis acidic sites. To elucidate the
origin of this cooperativity, a microkinetic model was constructed
using a recently published mechanism for the Lebedev reaction catalyzed
by MgO. The model was fit to our data using four fitting parameters.
The fitting suggests that adsorbed ethanol and hydrogen atoms have
a weaker bond with mixed-oxide MgO–SiO2 catalysts
than with bulk MgO catalysts, which we attribute experimentally to
an increase in the number of moderate-strength Mg2+–O2– site pairs formed at the expense of strongly basic
MgO sites.