Adsorbate-induced structural evolution changes the mechanism of CO oxidation on a Rh/Fe<sub>3</sub>O<sub>4</sub>(001) model catalyst

Jakub, Zdeněk; Hulva, Jan; Ryan, Paul T. P.; Duncan, David A.; Payne, David J.; Bliem, Roland; Ulreich, Manuel; Hofegger, Patrick; Kraushofer, Florian; Meier, Matthias; Schmid, Michael; Diebold, Ulrike; Parkinson, Gareth S.

doi:10.1039/c9nr10087c

Cited by 28 publications

(61 citation statements)

References 39 publications

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“…Our results show that, in contrast to Fe 3 O 4 (001), [ 33 ] neither the stoichiometric (1 × 1) surface nor the reduced (2 × 1) reconstruction of α‐Fe 2 O 3 (

1 \bar{1} 02

) stabilizes Rh adatoms at RT. However, on the (1 × 1) termination at least, single atoms can incorporate into the hematite lattice via a thermally activated process.…”

Section: Discussionmentioning

confidence: 66%

“…Note, however, that we could not recover the Rh to the surface by reducing the (1 × 1)‐terminated surface by UHV annealing, because Rh is also accommodated in the subsurface on the (2 × 1)‐terminated surface. We have shown previously that Rh atoms are stabilized on Fe 3 O 4 (001), [ 33 ] so perhaps an even stronger reduction of the surface could recover surface Rh species.…”

Section: Discussionmentioning

confidence: 99%

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Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe₂O₃(11¯02)

Kraushofer

Resch

Eder

et al. 2021

Adv Materials Inter

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Iron oxides (FeOx) are among the most common support materials utilized in single atom catalysis. The support is nominally Fe2O3, but strongly reductive treatments are usually applied to activate the as‐synthesized catalyst prior to use. Here, Rh adsorption and incorporation on the (11true¯02) surface of hematite (α‐Fe2O3) are studied, which switches from a stoichiometric (1 × 1) termination to a reduced (2 × 1) reconstruction in reducing conditions. Rh atoms form clusters at room temperature on both surface terminations, but Rh atoms incorporate into the support lattice as isolated atoms upon annealing above 400 °C. Under mildly oxidizing conditions, the incorporation process is so strongly favored that even large Rh clusters containing hundreds of atoms dissolve into the surface. Based on a combination of low‐energy ion scattering (LEIS), X‐ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) data, as well as density functional theory (DFT), it is concluded that the Rh atoms are stabilized in the immediate subsurface, rather than the surface layer.

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“…Our results show that, in contrast to Fe 3 O 4 (001), [ 33 ] neither the stoichiometric (1 × 1) surface nor the reduced (2 × 1) reconstruction of α‐Fe 2 O 3 (

1 \bar{1} 02

) stabilizes Rh adatoms at RT. However, on the (1 × 1) termination at least, single atoms can incorporate into the hematite lattice via a thermally activated process.…”

Section: Discussionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 99%

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe₂O₃(11¯02)

Kraushofer

Resch

Eder

et al. 2021

Adv Materials Inter

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“…This was previously observed for Rh and Ir adatoms on Fe 3 O 4 (001). 23 , 24 Because the two OH ligands are located in the same sites as water adsorbed at room temperature on the pristine α-Fe 2 O 3 (11̅02) surface, 18 no rearrangement is required to accommodate ad-Rh species as they are deposited. The facile diffusion of adatoms after deposition may be explained by Rh diffusing underneath the water ad-layer, as Rh can be handed over to neighboring OH groups.…”

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confidence: 99%

Single Rh Adatoms Stabilized on α-Fe₂O₃(11̅02) by Coadsorbed Water

et al. 2021

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Oxide-supported single-atom catalysts are commonly modeled as a metal atom substituting surface cation sites in a low-index surface. Adatoms with dangling bonds will inevitably coordinate molecules from the gas phase, and adsorbates such as water can affect both stability and catalytic activity. Herein, we use scanning tunneling microscopy (STM), noncontact atomic force microscopy (ncAFM), and X-ray photoelectron spectroscopy (XPS) to show that high densities of single Rh adatoms are stabilized on α-Fe 2 O 3 (11̅02) in the presence of 2 × 10 –8 mbar of water at room temperature, in marked contrast to the rapid sintering observed under UHV conditions. Annealing to 50 °C in UHV desorbs all water from the substrate leaving only the OH groups coordinated to Rh, and high-resolution ncAFM images provide a direct view into the internal structure. We provide direct evidence of the importance of OH ligands in the stability of single atoms and argue that their presence should be assumed when modeling single-atom catalysis systems.

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“…Prior CO oxidation studies report temperature-sensitivity of preferred mechanisms with both supported nanoparticle and atomically dispersed catalysts. 82,83 Figure 12 shows the shift in preference from TER CO pathway at low temperatures to LH (when O 2 adsorption is favored) at temperatures above 750 K. This is because kinetically relevant TDI and TDTS states vary with temperature. 3 At temperatures higher than 700 K, the TDI and TDTS of TER change to adsorbed CO and desorption of the first CO 2 , respectively.…”

Section: Discussionmentioning

confidence: 98%

Analysis of Preferred Mechanisms of CO Oxidation with Atomically Dispersed Pt1/TiO2 Using the Energetic Span Model

Bac

Sharada

2021

Preprint

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This work examines mechanisms of low-temperature CO oxidation over a single binding site of atomically dispersed Pt on rutile TiO2 (110) using density functional theory and the energetic span model (ESM). Of the 12 distinct pathways spanning Eley- Rideal (ER), termolecular ER (TER), Langmuir-Hinshelwood (LH), Mars-Van Krevelen (MvK) mechanisms as well as their combinations, TER with CO-assisted CO2 desorption yields the highest turnover frequency (TOF). However, this pathway is ruled out because Pt is dynamically unstable in an intermediate state in the TER cycle, determined in a prior ab initio molecular dynamics study by our group. We instead find, depending on reaction conditions, that either H1 is rendered inactive upon CO adsorption or the ER mechanism is preferred if O2 dissociatively adsorbs. ER exhibits the second highest TOF and the TOF-determining state is in qualitative agreement with experiment. TOFs for all MvK pathways are several orders of magnitude lower than ER and LH. By comparing TOFs for Pt1/TiO2 with prior mechanistic studies of various oxide-supported atomically dispersed catalysts in the literature, we identify the most active metal and support materials for low-temperature CO oxidation.

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

Abstract: The Rh1/Fe3O4(001) “single-atom” catalyst evolves differently upon exposure to O2 and CO, which results in distinct mechanisms of CO2 production.

Cited by 28 publications

References 39 publications

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe₂O₃(11¯02)

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe₂O₃(11¯02)

Single Rh Adatoms Stabilized on α-Fe₂O₃(11̅02) by Coadsorbed Water

Analysis of Preferred Mechanisms of CO Oxidation with Atomically Dispersed Pt1/TiO2 Using the Energetic Span Model

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

Abstract: The Rh1/Fe3O4(001) “single-atom” catalyst evolves differently upon exposure to O2 and CO, which results in distinct mechanisms of CO2 production.

Cited by 28 publications

References 39 publications

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe2O3(11¯02)

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe2O3(11¯02)

Single Rh Adatoms Stabilized on α-Fe2O3(11̅02) by Coadsorbed Water

Analysis of Preferred Mechanisms of CO Oxidation with Atomically Dispersed Pt1/TiO2 Using the Energetic Span Model

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

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe₂O₃(11¯02)

Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe₂O₃(11¯02)

Single Rh Adatoms Stabilized on α-Fe₂O₃(11̅02) by Coadsorbed Water