(469b) Coordination-Based Descriptors for Rational Design of Metal Nanocatalysts

Wang, S., Virginia Polytechnic Institute and State University
Xin, H., Virginia Polytechnic Institute and State University
One major challenge for designing metal nanocatalysts is to know a priori appropriate surface structure for a given catalytic reaction. Understanding the effects of particle morphology and composition on the interaction of surface atoms with adsorbates is of pivotal importance for identifying optimal active sites and engineering nanoparticles with maximized fraction of such sites. Many efforts have been made aiming to predict the binding energy of an adsorbate at metal surfaces using the electronic and/or geometric factors of the adsorption site (termed descriptor).1 While these models have been successfully used as reactivity descriptors for either extended-metal surfaces or simple metal nanoparticles, their extension to complex particle systems with varying strains and/or metal ligands remains elusive due to a formidable computational cost or the lack of an explicit consideration of interatomic interactions.

In this work, we used the previously developed reactivity descriptor, i.e., the orbital-wise coordination number (CNa), for understanding catalytic effects of size/shape/composition of metal nanocatalysts2. The CNa, quantified by interatomic coupling matrix elements between the site of interest and its all neighbors within a certain cutoff radius, provides a robust description of CO, O2, and O adsorption energies on Au metal nanoparticles of varying size and shape attributed to its explicit consideration of broken-bond strains. Furthermore, the CNa shows promise as a general descriptor for predicting adsorption properties of core-shell alloyed structures of Au nanoparticles with d10 metal ligands (e.g., Cu and Ag). We further tailored the metal ligands interacting with surface Pt atoms in a core-shell type alloy structure for a rapid screening of metal nanoparticle sites that have optimized activity toward O2 reduction. The approach can be readily extended to understand and predict reactivity trends of large and more complex metal catalysts with defects, impurities, transition-metal additions, supports, etc, and thus provides a general basis for rational design of metal nanocatalysts3

1. Hammer, B. & Nørskov, J. K. Electronic factors determining the reactivity of metal surfaces. Surf. Sci. 343, 211–220 (1995).

2. Ma, X. & Xin, H. Orbitalwise Coordination Number for Predicting Adsorption Properties of Metal Nanocatalysts. Phys. Rev. Lett. 118, 36101 (2017).

3. Wang, S. & Xin, H. Size Effects of Au Nanocatalysts: The Role of Local Coordination of Surface Atoms. Submitted (2017).