Screening strain sensitive transition metals using oxygen adsorption

Abstract

Nanocatalysts, due to their small size and/or lattice mismatch among hetero components, undergo strain. During a reaction, adsorbates as well as strain may cause the catalyst's surface to reorganize, which can lead to great changes in the reaction energetics and structures of reaction intermediates. Surface restructure is more prominent for certain metals than others. To better utilize strain to affect reaction, we need first to properly characterize transition metals according to their surface property change caused by adsorbates and strain. Using density functional theory (DFT) calculations, the synergistic effect of a representative adsorbate O* and strain (biaxial, ±5%) on the close-packed surfaces of 27 transition metals are systematically investigated. The metals can be roughly characterized as strain-sensitive or strain-insensitive using three descriptors: two variations of the O formation energy both in the absolute (ΔE_form) and relative sense (ΔE_form%), and the maximum vertical displacement of metal atoms (Z_i). For strain-sensitive metals, the criteria are ΔE_form > 0.60 eV, ΔE_form% > 20% and Z_i > 0.50 Å within the considered strain variation range. According to the isolated O* model, Zn and Cd are found to be strain-sensitive, while Zn, Cd, Pt, and Au are screened out as strain-sensitive metals when using the double-O* model with two neighboring O* adatoms, suggesting the categorization is strongly O coverage dependent. In principle, for these strain-sensitive transition metals, strain can be effectively utilized to control the energetics, selectivity, and mechanism of reactions involving O* adatoms.