Abstract
Accurately modelling the structure of a catalyst is a fundamental prerequisite for correctly predicting reaction pathways, but a lack of clear experimental benchmarks makes it difficult to determine the optimal theoretical approach. Here, we utilize the normal incidence X-ray standing wave (NIXSW) technique to precisely determine the three dimensional geometry of Ag1 and Cu1 adatoms on Fe3O4(001). Both adatoms occupy bulk-continuation cation sites, but with a markedly different height above the surface (0.43 ± 0.03 Å (Cu1) and 0.96 ± 0.03 Å (Ag1)). HSE-based calculations accurately predict the experimental geometry, but the more common PBE + U and PBEsol + U approaches perform poorly.
Highlights
Matthias Meier,a,b Zdeněk Jakub,b Jan Balajka,b Jan Hulva,b Roland Bliem,b Pardeep K
These adatoms were chosen for their nobility, in order to avoid undesired adsorption of the residual gases found in ultra-high vacuum, and are used as a comparatively simple benchmark with which to test the performance of theoretical calculations
We demonstrate via direct normal incidence X-ray standing wave (NIXSW) imaging, that Cu and Ag adatoms occupy a bulk-continuation cation site on the Fe3O4(001) surface
Summary
Matthias Meier,a,b Zdeněk Jakub,b Jan Balajka,b Jan Hulva,b Roland Bliem,b Pardeep K. We discovered that the (001) surface of a magnetite single crystal can stabilize ordered arrays of metal adatoms (e.g. Au,[44] Pd, and Pt46).[47] These adatoms were found to be homogenously distributed up to a comparatively high coverage and with high thermal stability, and is a promising model system to provide insight into single atom catalysts supported on FeOx nanocrystallites It is this remarkable density, stability, and homogeneity of adatom arrays that offers the opportunity to perform a precise structural determination, and test the ability of DFT-based calculations to accurately model these dispersed lone adatoms. We report a normal incidence X-ray standing waves (NIXSW48) study of two members of this family: Ag1 and Cu1 adatoms on Fe3O4(001) These adatoms were chosen for their nobility, in order to avoid undesired adsorption of the residual gases found in ultra-high vacuum, and are used as a comparatively simple benchmark with which to test the performance of theoretical calculations. Communication agreement can be achieved by constraining the lattice parameter to the experimental value, the failure to meet this experimental benchmark raises concern over this widely used functional in the field of adatoms on metal oxide surfaces
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