Probing the geometry of copper and silver adatoms on magnetite: quantitative experiment versus theory

Abstract

Benchmarking DFT calculations against precise normal incidence X-ray standing wave measurements.

Local Structure and Coordination Define Adsorption in a Model Ir1/Fe3O4 Single‐Atom Catalyst

“…Isolated Ir 1 adatoms appear as bright protrusions between the rows, as has been observed previously for a variety of other metals on this surface . The adsorption site is essentially where the next tetrahedrally coordinated Fe cation would reside in the spinel structure, suggesting a two‐fold coordination to the substrate. This is in line with our DFT calculations (optB88‐DF, U eff =3.61 eV), which find a strong binding energy (−5.2 eV with respect to a single Ir atom in the gas phase) and small positive Bader charge of 0.5 e for an Ir adatom in this position.…”

Adsorbate-induced structural evolution changes the mechanism of CO oxidation on a Rh/Fe3O4(001) model catalyst

“…been shown previously to support dense arrays of single metal atoms, preventing the adatom mobility and cluster formation even at elevated temperatures. 15,24,[26][27][28] This is due to the existence of highly stable adsorption sites with a nearest-neighbour distance of 0.84 nm, in which the adatoms are 2-fold coordinated to the surface oxygen atoms, essentially occupying a bulk continuation tetrahedral site (schematic representation shown in the uppermost inset of Fig. 2a).…”

Direct measurement of Ni incorporation into Fe3O4(001)

“…In our prior work, 18 the adatom adsorption site of Cu and Ag was determined, quantitatively, utilising the normal incidence X-ray standing wave (NIXSW) technique. Specifically, Cu and Ag adatoms were found to bridge two surface oxygen atoms in a site comparable to that of bulk tetrahedral iron, but at significantly different adsorption heights.…”

“…More importantly, STM cannot image sub-surface topography and, as such, it is only the effect on the electronic structure at the surface of the potentially incorporated adatoms that is measured. Furthermore, our prior work 18 has cast doubt on the accuracy of DFT+U calculations for modelling adatoms on the magnetite surface. As both the catalytic activity of metal nanoclusters on Fe 3 O 4 supports, and the SCV structure that patterns the dispersion of these lone adatoms on the (001) surface of Fe 3 O 4 , are intrinsically linked to the cation vacancies, the step-wise incorporation of Ni atoms into these vacancies could provide a unique opportunity to probe the cation defect chemistry of magnetite.…”