(520b) Metal Core/Surface Oxide Shell Catalysts for C-O Bond Activation

Authors: 
Mironenko, A. V., University of Delaware
Goulas, K., University of Delaware
Gorte, R. J., University of Pennsylvania
Murray, C. B., University of Pennsylvania
Vlachos, D., University of Delaware
C-O bond scission is a key step for a variety of industrial processes ranging from Fischer-Tropsch synthesis to valorization of biomass. Bimetallic catalysts involving a base metal and a noble metal were found to be particularly effective for C-O bond activation in a variety of O-containing molecules (diols and triols, furans, pyrans, etc.). For example, recently it was shown that monodisperse nanocrystals (NC) with the Pt3Co2 stoichiometry are capable of converting 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) in the liquid phase with up to the 99% yield at moderate temperatures and pressures (180oC, 33 bar H2)1.

Herein, we use a combination of the state-of-the-art density functional theory, ab initio molecular dynamics coupled with simulated annealing, and microkinetic modeling to elucidate the structure and properties of the NC catalytic site. In addition, we develop a geometric model that allows comparison of first principlesâ?? structure predictions with in situ EXAFS/XANES measurements and ex situ XRD data. A bimetallic alloy core/surface oxide shell structure with Co segregated to the surface is found to be consistent with the experimental data. We identify the strong interaction between the CoxOy surface oxide and the underneath metal to be crucial for the kinetic stability of the oxide in a highly reducing environment. Finally, we elucidate the â??reverse Mars van Krevelenâ? mechanism of hydrogenolysis.

References:

1. Luo, Yun, Mironenko, Goulas, et al. Mechanisms for High Selectivity in Hydrodeoxygenation of 5-Hydroxymethylfurfural over PtCo Nanocrystals. Under Review.