Modeling single-atom reactivity
Noble metals often perform best for demanding reactions such as oxygen reduction, an effect often explained by the position of their d-band. One way to minimize the cost of noble metals is to disperse them as single atoms. To model the reactivity of supported single atoms, Hulva et al. evaporated different transition metals such as nickel, silver, and iridium on an Fe3O4(001) support. Single atoms adsorbed in the same twofold site between underlying rows of surface iron atoms. In studies of CO adsorption as a proxy for reactivity, the d-band was strongly affected by the charge transfer to the support and CO-induced structural changes. These effects can weaken the adsorption energy compared with the expected values based on electronic structure alone.
Science, this issue p. 375
Understanding how the local environment of a “single-atom” catalyst affects stability and reactivity remains a challenge. We present an in-depth study of copper1, silver1, gold1, nickel1, palladium1, platinum1, rhodium1, and iridium1 species on Fe3O4(001), a model support in which all metals occupy the same twofold-coordinated adsorption site upon deposition at room temperature. Surface science techniques revealed that CO adsorption strength at single metal sites differs from the respective metal surfaces and supported clusters. Charge transfer into the support modifies the d-states of the metal atom and the strength of the metal–CO bond. These effects could strengthen the bond (as for Ag1–CO) or weaken it (as for Ni1–CO), but CO-induced structural distortions reduce adsorption energies from those expected on the basis of electronic structure alone. The extent of the relaxations depends on the local geometry and could be predicted by analogy to coordination chemistry.