Carboxylic acid induced near-surface restructuring of a magnetite surface

Björn Arndt,Vedran Vonk,Marcus Creutzburg,Kai Sellschopp,Gregor B V Feldbauer,Elin Grånäs,Stefan Müller,Andreas Stierle,Konstantin Krausert,Heshmat Noei

doi:10.1038/s42004-019-0197-1

Abstract

A fundamental knowledge of the interaction of carboxylic acids, such as formic acid, with magnetite surfaces is of prime importance for heterogeneous catalysis and the synthesis of novel materials. Despite this, little is known about the atomic scale adsorption mechanisms. Here we show by in-situ surface X-ray diffraction that the oxygen rich subsurface cation vacancy reconstruction of the clean magnetite (001) surface is lifted by dissociative formic acid adsorption, reestablishing a surface with bulk stoichiometry. Using density functional theory, the bulk terminated, fully formic acid covered surface is calculated to be more stable than the corresponding clean, reconstructed surface. A comparison of calculated and experimental infrared bands supports the bidentate adsorption geometry and a specific adsorption site. Our results pave the way for a fundamental understanding of the bonding mechanism at carboxylic acid/oxide interfaces.

Highlights

A fundamental knowledge of the interaction of carboxylic acids, such as formic acid, with magnetite surfaces is of prime importance for heterogeneous catalysis and the synthesis of novel materials
A reference surface X-ray diffraction (SXRD) data set of the clean, subsurface cation vacancy (SCV) reconstructed surface was recorded under ultra high vacuum (UHV) conditions at room temperature, see Fig. 1
We have determined the atomic structure of the formic acid/ magnetite (001) interface by a combination of surface X-ray diffraction and density functional theory

Summary

Introduction

A fundamental knowledge of the interaction of carboxylic acids, such as formic acid, with magnetite surfaces is of prime importance for heterogeneous catalysis and the synthesis of novel materials. A fundamental knowledge of the atomic structure of oxide/carboxlic acid interfaces is required for a deeper understanding of the adsorption energetics and thermodynamics, as well as possible intermediate steps involved in reactions and adsorption induced changes in the interfacial geometric and electronic structure. These serve as a basis for the theoretical prediction of reactions paths, as well as the mechanical properties of hierarchical materials. We present a combined surface X-ray diffraction (SXRD) and density functional theory (DFT) study of the atomic structure of the magnetite (001)/formic acid interface This combination of methods is especially suited to address adsorption induced structural changes in the near surface region.

Methods

Results

Conclusion