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

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 (180^oC, 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 Co_xO_y 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.