Abstract
In this work, the adsorption height of Ag adatoms on the Fe3O4(001) surface after exposure to CO was determined using normal incidence x-ray standing waves. The Ag adatoms bound to CO (Ag1 CO) are found to be pulled out of the surface to an adsorption height of 1.15 Å ± 0.08 Å, compared to the previously measured height of 0.96 Å ± 0.03 Å for bare Ag adatoms and clusters. Utilizing DFT+vdW+U calculations with the substrate unit cell dimension fixed to the experimental value, the predicted adsorption height for Ag1 CO was 1.16 Å, in remarkably good agreement with the experimental results.
Highlights
A recent drive in the field of heterogeneous catalysis is the complete dispersion of the catalytically active metal into isolated centers, so called single atom catalysts (SACs)
AgChiOgh, with a binding energy shift of 0.6 eV with respect to Agbare, comparable to the 0.7 eV shift found for CO exposure to Ir,21 was assigned to Ag adatoms coordinated to CO molecules (AgC1 O in the following)
We demonstrate that the CO molecule pulls the silver adatom out of the Fe3O4(001) surface by 0.19 Å ± 0.08 Å, compared to the value measured for a mixture of uncoordinated Agb1are adatoms and Ag nanoclusters, to an adsorption height of 1.15 Å ± 0.08 Å above a projected bulk like Feoct termination
Summary
A recent drive in the field of heterogeneous catalysis is the complete dispersion of the catalytically active metal into isolated centers, so called single atom catalysts (SACs). SACs have been used to tackle the poisoning of heterogeneous catalysts [e.g., the use of an atomically dispersed Pt single atom alloy (SAA)].8. Development of such SACs is highly reliant on accurate density functional theory (DFT) calculations for predicting reaction mechanisms to understand measured catalytic activity and for improving the screening of new catalytic materials.. Development of such SACs is highly reliant on accurate density functional theory (DFT) calculations for predicting reaction mechanisms to understand measured catalytic activity and for improving the screening of new catalytic materials.2,9–13 These DFT calculations can only be validated by comparison to quantitative experiments. The geometric structure of an adsorbate is an important bellwether of the accuracy of such calculations, as it is intrinsically linked to both the electronic structure of the system and the potential reaction mechanisms and pathways that are sterically available
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