The pioneering work by N�rskov and co-workers on the application of density functional theory (DFT), linear scaling relations and the resulting volcano curve in heterogeneous catalysis has made it possible to predict a pool of promising monofunctional material candidates for various catalytic processes computationally  [1]. In the literature, however, several examples of high performance catalysts with multiple site-specific functionalities at steady-state have been reported  [2�4]. The most common systems consist of two distinct sites that catalyze different reaction steps independently and are often referred to as �bifunctional catalysts�. Using DFT and microkinetic modeling, we aim to understand the mechanisms that are responsible for bifunctional activity and provide a computational framework for screening of bifunctional catalysts. Our results indicate that there are theoretical limits for the achievable activity improvement, which depend on the slope of the underlying scaling relation. For steep volcano curves activity improvements through bifunctional mechanisms are feasible when the diffusion barrier between active sites is within 0.2 to 0.5 eV. However, bifunctional catalysts do not necessarily outperform monofunctional systems. More specifically, for CO oxidation we found that the overall activity is not significantly altered when bifunctional catalysts are considered, but equally active bifunctional catalysts may be tailored from less active and cheaper components.[1]       J. K. N�rskov, T. Bligaard, J. Rossmeisl, and C. H. Christensen, Nature Chemistry 1 , 37�46 (2009).[2]       M. Kotobuki, A. Watanabe, H. Uchida, H. Yamashita, and M. Watanabe, Journal of Catalysis 236 , 262�269 (2005).[3]       M. Neurock, Industrial & Engineering Chemistry Research 49 , 10183�10199 (2010).[4]       G. Kyriakou, M. B. Boucher, A. D. Jewell, E. A. Lewis, T. J. Lawton, A. E. Baber, H. L. Tierney, M. Flytzani-Stephanopoulos, and E. C. H. Sykes, Science 335 , 1209�1212 (2012).

Computational evaluation of steady-state bifunctional catalysis

247th National Meeting (2014)

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