Propylene epoxidation reaction was investigated on catalytic surfaces of chlorinated
copper(I) oxide and ruthenium(IV) oxide using periodic density functional theory
(DFT). Cu2O(001) and (110) surface of RuO2 was selected to generate chlorinated
surfaces to be used in the study. Besides epoxidation, other reactions that compete
with epoxidation were also studied such as formations of allyl-radical, acrolein,
acetone on chlorinated Cu2O(001) and formations of propionaldehyde, allyl-radical
and acetone on chlorinated RuO2(110) surface. Path of each reaction was
determined by CI-NEB method and transition state analyses. Generally accepted
stable surface intermediate mechanism was utilized in reactions to final products.
The surface intermediate favorable on the surfaces in this study was determined to
be the intermediate that is not preferable on metallic surfaces under low oxygen.
On chlorinated Cu2O(001) surface, formation of propylene oxide, acetone and
acrolein have higher probability than gas phase allyl-radical since the desorption
energy of allyl-radical was calculated to be 70kcal/mol which is a relatively high
value. In fact it is desirable since gas phase allyl-radical is known to be the
precursor of combustion products. On chlorinated RuO2(110) surface, desorption Propylene epoxidation reaction was investigated on catalytic surfaces of chlorinated
copper(I) oxide and ruthenium(IV) oxide using periodic density functional theory
(DFT). Cu2O(001) and (110) surface of RuO2 was selected to generate chlorinated
surfaces to be used in the study. Besides epoxidation, other reactions that compete
with epoxidation were also studied such as formations of allyl-radical, acrolein,
acetone on chlorinated Cu2O(001) and formations of propionaldehyde, allyl-radical
and acetone on chlorinated RuO2(110) surface. Path of each reaction was
determined by CI-NEB method and transition state analyses. Generally accepted
stable surface intermediate mechanism was utilized in reactions to final products.
The surface intermediate favorable on the surfaces in this study was determined to
be the intermediate that is not preferable on metallic surfaces under low oxygen.
On chlorinated Cu2O(001) surface, formation of propylene oxide, acetone and
acrolein have higher probability than gas phase allyl-radical since the desorption
energy of allyl-radical was calculated to be 70kcal/mol which is a relatively high
value. In fact it is desirable since gas phase allyl-radical is known to be the
precursor of combustion products. On chlorinated RuO2(110) surface, desorption
observed to be possible on chlorinated RuO2(110) surface but not possible on
chlorinated Cu2O(001). When activation barriers and desorption energies of all
possible reactions are compared on chlorinated RuO2(110) surface / gas phase
propylene oxide generated directly seems as the preferable product with allylradical
although it was computed to have high desorption energy.
Comparison of activation barriers obtained in this study on chlorinated Cu2O(001)
with the barriers of nonchlorinated surface revealed chlorine slightly increases the
activation barrier of unwanted allylic hydrogen stripping and hence slightly
decreases the probability of occurance. When chlorine is placed closer to reaction
site, activation barrier of allylic hydrogen stripping reaction increases further. The
effect of chlorine might be electronic since the charge of oxygen at reaction site
slightly becomes less negative when the place of chlorine gets closer to the reaction
site on the surface. Similar comparison between chlorinated and nonchlorinated
RuO2(110) surfaces revealed that chlorine addition does not improve the surface
toward propylene oxide formation, rather it is detrimental as chlorine addition
caused a decrease in unwanted allylic hydrogen stripping reaction.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12613918/index.pdf |
| Date | 01 November 2011 |
| Creators | Kurnaz, Emine |
| Contributors | Onal, Isik |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for METU campus |
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