Computational Strategies for Identification of Bimetallic Ethylene Epoxidation Catalysts
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A combination of quantum mechanical techniques and microkinetic modeling has been employed to explore improved catalysts than Ag for the ethylene epoxidation process. A combination of 10 bimetallic catalysts and pure Ag was investigated. Rather than carrying out a large number of computationally expensive Nudged Elastic Band calculations on periodic slabs, a cluster approach was employed by assuming the same transition state on different bimetallic catalysts as that on pure Ag. This approach results in tremendous computational savings, while maintaining reasonable accuracy. On the basis of the density functional theory (DFT) calculations for the oxametallacycle (OME) branching reactions, only AgCu, AgPd, and AgPt are predicted to be better catalysts than pure Ag for EO selectivity. Microkinetic modeling was used to incorporate the DFT results into amore comprehensive model and AgCu was found to be the only bimetallic catalyst that results in significantly higher EO selectivity than pure Ag. According to the microkinetic analysis, AgPd and AgPt do not lead to improved selectivity because of the high stability of the OME on these catalysts. Overall, this study confirms that AgCu is the only promising bimetallic catalyst out of the 10 combinations considered. 2008 Elsevier B.V. All rights reserved.
