20.500.12556/RUNG-5539-f4e021ed-9ad7-0807-3b82-d9b20515af64
Effect of Na, Cs and Ca on propylene epoxidation selectivity over CuOx/SiO2 catalysts studied by catalytic tests, in-situ XAS and DFT
This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified
CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination
of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO
clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic
reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between
propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene
reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of
propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the
exothermicity of O2 dissociation. The Na induced Cu-O bond modification decreases the
activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step
in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst.
At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the
abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation
barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping
decreases to 0.16 eV.
Alkali modification
propylene epoxidation
reaction mechanism
copper oxide
activation barrier.
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false
Slovenski jezik
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2020-06-05 13:23:06
2020-06-05 16:19:34
2023-06-09 03:39:08
0000-00-00 00:00:00
2020
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2020
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Zaloznikova
NiDoloceno
NiDoloceno
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18333187
https://doi.org/10.1016/j.apsusc.2020.146854
URN:SI:UNG:REP:N6ZFJTN0
Univerza v Novi Gorici
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