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Published on: July 18, 2017
Ag-Cu catalysts for ethylene epoxidation: selectivity and activity descriptors
Ngoc Linh Nguyen1, Stefano de Gironcoli, Simone Piccinin
1Scuola Internazionale Superiore di Studi Avanzati (SISSA), via Bonomea 265, I-34136 Trieste, Italy.
The Journal of Chemical Physics
|May 17, 2013
Summary
Silver-copper alloy catalysts improve ethylene epoxidation selectivity by forming thin oxide layers. These layers enhance ethylene oxide production by tuning metal-carbon and metal-oxygen bond strengths.
Area of Science:
- Catalysis
- Materials Science
- Surface Chemistry
Background:
- Silver-copper (Ag-Cu) alloy catalysts offer higher selectivity for ethylene epoxidation than pure silver (Ag).
- Under oxidizing conditions, copper (Cu) forms thin oxide layers on Ag surfaces, influencing catalytic performance.
Purpose of the Study:
- To investigate the reaction mechanism on Ag-Cu oxide layer structures using first-principles atomistic simulations.
- To identify the reasons behind the enhanced selectivity of Ag-Cu alloy catalysts in ethylene epoxidation.
Main Methods:
- Density functional theory (DFT) based first-principles atomistic simulations.
- Extension and refitting of the Kokalj selectivity descriptor to include thin oxide layer catalysts.
Main Results:
- The selectivity of Ag-Cu catalysts is primarily governed by the relative strengths of metal-carbon versus metal-oxygen bonds.
- Reaction barrier heights are mainly dependent on the binding energy of the oxametallacycle intermediate.
Conclusions:
- Thin oxide layers on Ag-Cu alloys are key to improved ethylene oxide selectivity.
- The modified selectivity descriptor accurately predicts catalytic performance based on binding energies and bond strengths.
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