Reversible structural transformation of FeOx nanostructures on Pt under cycling redox conditions and its effect on oxidation catalysis

Abstract

a Understanding dynamic changes of catalytically active nanostructures under reaction conditions is a pivotal challenge in catalysis research, which has been extensively addressed in metal nanoparticles but is less explored in supported oxide nanocatalysts. Here, structural changes of iron oxide (FeO x ) nanostructures supported on Pt in a gaseous environment were examined by scanning tunneling microscopy, ambient pressure X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy using both model systems and real catalysts. O-Fe (FeO) bilayer nanostructures can be stabilized on Pt surfaces in reductive environments such as vacuum conditions and H 2 -rich reaction gas, which are highly active for low temperature CO oxidation. In contrast, exposure to H 2 -free oxidative gases produces a less active O-Fe-O (FeO 2 ) trilayer structure. Reversible transformation between the FeO bilayer and FeO 2 trilayer structures can be achieved under alternating reduction and oxidation conditions, leading to oscillation in the catalytic oxidation performance.

Metal/oxide interfacial effects on the selective oxidation of primary alcohols

“…3), Fe 2p 3/2 peak from O-FeO/Pt(111) (709.3 eV) is only slightly more positive than that of Fe-FeO/Pt(111) (708.6 eV), indicating the Fe 2+ state of FeO nanostructures, regardless of their step termination. Fe 3+ on Pt(111) should give a Fe 2p 3/2 peak at above 710 eV, as shown in the previous study22. Supplementary Figure 4 shows the surface of O-FeO/Pt(111) after an exposure of ∼0.4 L (1 L=1.0 × 10 -6   Torr s) benzyl alcohol at room temperature.…”

Enhanced CO Oxidation on the Oxide/Metal Interface: From Ultra‐High Vacuum to Near‐Atmospheric Pressures

“…The reaction rate was measured by monitoring the CO/Pt related signal in ultraviolet photoelectron spectra upon dosing of 5×10 −8 mbar O 2 to the CO presaturated surface at room temperature. Although Bao’s group confirmed the formation of FeO 2 trilayer islands upon oxidation of the “as grown” films at sub‐monolayer coverages, they claim that these O‐rich islands are inert 11. The latter statement is at variance with our results, which clearly showed enhanced reactivity of the closed FeO 2 films.…”

“…8a Following these studies, the highest reactivity on FeO(1 1 1)/Pt(1 1 1) must be obtained on the FeO 1− x islands, which are oxygen deficient at the rim and expose the unsaturated Fe cations. As a proof, in this9c and following‐up publications,9a, 11 the authors provided a linear relationship obtained between the CO oxidation activity and the perimeter length only measured on the 0.25 ML FeO(1 1 1)/Pt(1 1 1) sample that underwent gradual oxide sintering upon stepwise annealing. The reaction rate was measured by monitoring the CO/Pt related signal in ultraviolet photoelectron spectra upon dosing of 5×10 −8 mbar O 2 to the CO presaturated surface at room temperature.…”

“…The discrepancy could, in principle, be linked to the differences in oxide preparation 12. Indeed, Bao and co‐workers found that UHV annealing at 573 K is sufficient to reduce FeO 2 back to FeO,11 whereas the reduction only occurs at temperatures as high as 850 K in our films 8a. On the other hand, the apparent controversy may be related to the reaction conditions and methods by which the reactivity was measured.…”

Construction of ultrafine and stable PtFe nano-alloy with ultra-low Pt loading for complete removal of CO in PROX at room temperature

“…6, the desorption signal for Pt 0.71 Fe 0.23 /Al 2 O 3 after PROX reaction arises at about 225 • C, which is the same as the fresh sample. This means the oxidation of Fe species during RPOX reaction won't affect the adsorption strength of CO. As reported previously [63], Fe 2+ are the active site for the activation of oxygen, while it is hard for Fe 3+ to activate O 2 . Thus, it can be concluded that the oxidation of Fe 2+ to Fe 3+ decreases the ability of O 2 activation, and thus leads to the loss of activity during PROX reaction.…”