Influence of Strain on Acid–Basic Properties of Oxide Surfaces

Jannik P Roth,Gianfranco Pacchioni

doi:10.1021/acs.jpcc.0c05913

Jannik P Roth, Gianfranco Pacchioni

Open Access

https://doi.org/10.1021/acs.jpcc.0c05913

Copy DOI

Abstract

The surface of oxide nanostructures (nanoparticles, nanowires, and epitaxial thin films) can be significantly strained compared to the regular crystallographic surfaces. In this work, using density functional theory methods, we studied the dependence of properties of MgO(100), CaO(100), SrO(100), BaO(100), anatase TiO2(101), and tetragonal ZrO2(101) surfaces (band gap, work function) on external tensile and compressive strain from +4 to −4%. To probe the acid sites, the adsorption of CO as a probe molecule was investigated. In most cases, tensile strain favors the adsorption of CO, while compressive strain weakens it. To also probe the anionic basic sites, we used H2O as a probe molecule. On most surfaces, two competing adsorption modes (molecular and dissociative) are present. Applying strain has a different effect on the adsorption modes. On t-ZrO2, we can invert the stability order of molecular and dissociative adsorption by applying 1.4% biaxial tensile strain. We described the dependency of different properties on strain with a simple empirical model with only three fitting parameters. This allows for a precise interpolation of our data and gives the opportunity to predict surface properties of strained surfaces.

Highlights

Modifying surface properties is a potential way to improve performances of existing catalysts or to design new catalysts
For the alkaline-earth oxides with cubic structure, we considered the most stable (100) surface; because titania and zirconia have various polymorphs, we considered the (101) face of anatase TiO2 (a-TiO2) and the (101) face of tetragonal ZrO2 (t-ZrO2)
Lattice constants taken from bulk optimization or from bulk experimental data are often used in modeling oxide surfaces

Summary

Introduction

Modifying surface properties is a potential way to improve performances of existing catalysts or to design new catalysts. Among the properties of interest in surface chemistry, are the acidity and basicity of surface sites, as these determine the interaction with adsorbed molecules. The modification of these properties can be done via doping, interfacing, and nanostructuring. This can result in electronic modifications (e.g., by varying the position of donor or acceptor levels on a given site) or by structural modifications (e.g., by varying the coordination of a specific site). Elastic strain plays an important role in changing the surface properties and influencing the reactivity. It remains challenging to precisely measure the amount of strain and changes in the surface properties experimentally

Methods

Results

Conclusion