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Structure- and Temperature-Dependence of Pt-Catalyzed Ammonia Oxidation Rates and Selectivities
journal contribution
posted on 2019-01-31, 00:00 authored by Hanyu Ma, William F. SchneiderAmmonia oxidation
is operated at different temperatures over Pt
catalysts of different structures to recover different products. In
this work, we elucidate the dependency of ammonia oxidation rates
and selectivities on both Pt structure and temperature. We perform
density functional theory (DFT) computations to compare the reaction
and activation energies of elementary reactions on Pt(211) and Pt(111).
We develop a microkinetic model parametrized with the DFT results.
We show that barriers to product formation are lower on stepped Pt
than on terrace, leading to a much higher step rate at low temperature
to selectively oxidize ammonia to nitrogen. At high temperature, however,
both step and terrace perform comparably in rate to selectively produce
nitric oxide. While N2 is always the thermodynamic product,
relative N and O coverages interact to make NO the kinetic product
at high temperature. The predicted rate and selectivity are consistent
with experiments. We further show rate-controlling steps on the two
Pt surfaces are different at low temperature but are the same at high
temperature. The degrees of selectivity control for elementary reactions
are comparable for the two surfaces. Finally, we demonstrate the flows
of elementary reactions in the reaction network are also structure-
and temperature-dependent.
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show rate-controlling stepsselectivity controlactivation energiesN 2step ratePt-Catalyzed Ammonia Oxidation Ratesammonia oxidation ratesPt structurereaction networkmicrokinetic model parametrizedoxidize ammoniaPt catalystsnitric oxideDFT resultsSelectivities Ammonia oxidationO coveragesproduct formationPt surfaces
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