(617cm) Predicting Surface Intermixing in Alloy Nanocatalysts from First Principles Calculations

Luke T. Roling and Manos Mavrikakis

Department of Chemical & Biological Engineering,
University of Wisconsin-Madison, Madison, WI

Controlled catalyst design and
synthesis are enhanced by a detailed fundamental understanding of phenomena
occurring at the catalyst surface. One such class of phenomena that has long
attracted attention is metal adatom diffusion across metal substrates, and the
impact these phenomena have on catalyst growth.^1-2 We recently
described the synthesis and electrochemical activity of hollow Pt-Pd nanocages with exceptional performance for the oxygen
reduction reaction.³ Detailed DFT calculations predicted that the
formation of these nanostructures, which occurred through etching Pd from a Pd-Pt core-shell
structure, requires intermixing of Pt and Pd during
the core-shell synthesis. This intermixing was accommodated by the ease of
substitution of Pt into the underlying Pd substrate
relative to the diffusion of Pt across the surface.

In this presentation, we extend
these calculations to bimetallic combinations of ten transition metals to
predict similar intermixing phenomena in the synthesis of other
catalytically-relevant alloy nanocatalysts. In
particular, we present results for metal adatom surface diffusion and
substitution for all combinations of eight fcc and two hcp metals, considering both close-packed and open crystal facets.
We also present results at two different surface coverages of metal adatoms.
Our results can guide future simulation and inorganic synthesis efforts toward
the atomic-scale design of nanocatalysts with
controlled structures and compositions.

1. P. J. Feibelman, Physical Review Letters 1990,
65, 729.

2. T. Ala-Nissila, R. Ferrando, S. Ying, Advances
in Physics 2002, 51, 949.

3. L. Zhang, L. T. Roling, X. Wang, M. Vara, M. Chi, J. Liu, S. Choi, J. Park,
J. A. Herron, Z. Xie, M. Mavrikakis, Y. Xia, Science 2015, 349, 412.