Engineering Chemical and Catalytic Activity of Metal Surface Sites by Controlling Strain and Ligand Effects in Nonmodel Nanoparticle Catalysts

Abstract

Binding energy of reactants on heterogeneous catalyst surface sites is a well-established catalytic activity descriptor for many chemical reactions. However, systematically manipulating the binding energies by engineering the catalytic surface sites has proven challenging. Herein, we propose a nanoparticle catalyst structure that contains an alloy core composed of miscible metal atoms, surrounded by layers of a different material, and covered by a layer of catalytically active metal. The alloy core controls the lattice strain of the nanoparticle and therefore the distance between the surface atoms, while the subsurface layer atoms induce a ligand effect on the surface atoms. We show that this class of materials allows us to systematically control the adsorbate binding energies with high precision. We illustrate our findings by developing nonmodel nanoparticle catalysts that employ an AuCu alloy with controlled composition as the core, Au as the surrounding layers, and Pt as the active surface metal. Electrochemical CO stripping measurements suggest that the CO binding energy on the surface Pt sites can be systematically tuned by varying the composition of the alloy core. Our analysis suggests that the change in the CO binding energy of Pt is the result of the combined ligand effect from the Au layers and strain effect from the AuCu core. The presented catalyst structure allows for precise modulation of the strain and ligand effect for tuning the local chemical environment of any catalytic materials, which may aid the development of next-generation catalysts.