Unraveling CO adsorption on model single-atom catalysts

Abstract

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.

Engineering Single Atom Catalysts to Tune Properties for Electrochemical Reduction and Evolution Reactions

“…The coupled effects of local structural distortions and adsorption energy tuning have been broadly demonstrated in metals with nearly filled d ‐shells. [ 51 ] However, the strong CO binding on Ir surfaces, shown in Figure 2c, was apparently determined by electrostatic bonding consistent with studied Ni based systems. While initially two‐fold coordinate, Ir 1 bonds to subsurface O after binding to single CO molecules, forming a pseudo‐square‐planar Ir geometry.…”

“…Correlative d ‐band models, which were originally constructed to link CO‐metal orbital overlap and coupling to corresponding CO adsorption energy contributions on extended metal surfaces, are frequently implemented to investigate oxide‐supported metal NP catalyst reactivity. [ 51,52 ] However, such models characterize Co‐metal bonding over hybridized orbitals with integer, ionic formal charges. [ 68–71 ] Such characterization does not treat SACs effectively, as isolated metal atoms are bonded to supports and frequently have non‐zero partial charges.…”

“…In contrast, the stable four‐fold coordination observed by group 10 metals, such as Pd and Pt, in their bulk oxides energetically improves their ability to adapt five‐fold coordination environments. [ 51 ] However, incorporation of four‐fold coordinated SACs still fails when metal aggregation is sufficiently induced through processes such as sintering. Nevertheless, Ni and group 9 metals that can assume octahedral oxide coordination environments have higher oxygen affinities, which can avoid such aggregation to facilitate incorporation into lattices.…”

“…[ 49,50 ] Practically, SACs featuring no agglomeration would fully utilize metal atom surface area in reactions, which is particularly useful for catalysis involving noble metals such as Pd, Ir, Au, and Pt. [ 47,48,50 ] Idealized isolation of these single metal atoms would additionally produce excellent model systems, [ 51–54 ] which could be studied to better understand the sophisticated atomic‐scale mechanisms undergirding heterogeneous catalysis.…”

Unraveling the role of oxygen vacancy in the electrooxidation of 5-hydroxymethyfurfural on Co3O4

“…12,13,14 The adsorption/desorption behavior is regarded as a critical step in the catalytic process. 15,16,17 OH ad is the crucial intermediate for the oxygen evolution reaction (OER) and alcohol molecules catalytic cycle, which has been widely recognized the reaction mechanism. 18,19,20 In ethanol oxidation, the H* derived from the dehydrogenation of hydroxyl groups is combined with OH ad in the alkaline solution.…”