Reduction behavior of oxidized Pd(100) and Pd75Ag25(100) surfaces using CO

Fernandes, V. R.; Gustafson, Johan; Svenum, Ingeborg-Helene; Farstad, Mari Helene; Walle, L. E.; Blomberg, Sara; Lundgren, Edvin; Borg, A.

doi:10.1016/j.susc.2013.10.018

Cited by 18 publications

(25 citation statements)

References 87 publications

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“…In the phase coexistence region, it is conceivable that the interplay between surface oxide formation, decomposition, and CO adsorption makes available surface phases that are reactive toward CO oxidation. For instance, the oxygen atom in the surface oxide could be reduced by adsorbed CO at the reduced surface as shown both experimentally 51 and theoretically. 49,50 Consequently, surface oxide at the perimeter region is destabilized at the coexisting interface and then reduced to metastable oxygen-containing phases, such as the 0.25 or 0.5 ML phases.…”

Section: Methodsmentioning

confidence: 87%

CO Oxidation on the Pd(111) Surface

Duan

Henkelman

2014

ACS Catal.

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Under technologically relevant oxygen-rich conditions, the reaction mechanism of CO oxidation over transition metals can be complicated by the formation of oxides. Questions of whether the active surface for CO oxidation is a pristine metal, a surface oxide, or a bulk oxide is still under active debate. In this study, density functional theory calculations are used to model CO oxidation on the Pd(111) surface. Our results show that a thin layer of Pd 5 O 4 surface oxide is stable under catalytically relevant gas-phase conditions. Three-fold oxygen atoms in the surface are found to react with gas-phase CO molecules following an Eley−Rideal reaction mechanism. Such CO oxidation reduces the surface oxide, but the oxide can be replenished by O 2 dissociation. Kinetic analysis shows that experimentally observed reaction conditions, that are uninhibited by CO and limited only by mass transfer, correspond to a surface oxide phase with CO oxidation occurring though the Eley−Rideal mechanism. Under steadystate operating conditions, the continuous formation and decomposition of the surface oxide is expected and is key to the high CO oxidation rate on Pd(111).

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Section: Methodsmentioning

confidence: 87%

CO Oxidation on the Pd(111) Surface

Duan

Henkelman

2014

ACS Catal.

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“…Until today, only in‐situ high pressure SXRD has been performed to study the kinetics of the bulk PdO formation. The bulk PdO formed on Pd(111) and Pd(100) have been reported to be kinetically hindered below 250 °C and 400 °C by, respectively, Lundgren and Kasper et al, The reduction behavior of oxidized Pd on Pd(111) and Pd(100), was studied using in‐situ XPS by decreasing the oxygen pressure, increasing temperature, and/or using CO gas.…”

Section: Introductionmentioning

confidence: 99%

In‐Situ TEM on Epitaxial and Non‐Epitaxial Oxidation of Pd and Reduction of PdO at P = 0.2–0.7 bar and T = 20–650 °C

2016

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The oxidation of Pd particles and subsequent reduction of PdO were studied in 0.2-0.7 bar O 2 and H 2 gas at 20-650°C by in-situ transmission electron microscopy. The 15 nm thick Pd particles were 50-300 nm wide, and (111) oriented on the SiN support. Two oxidation mechanisms were observed: 1) the slow formation of epitaxial PdO at the Pd particle edges with orientations OR (1): PdO[201]//Pd[111] and PdO(020)// Pd{022}, 5.8°from OR(2): PdO[110]//Pd[100] and PdO[001]// Pd[001]. 2) the fast formation of randomly oriented PdO nucle-[a]

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“…On the other hand, Fernandes et al showed that the reduction rate increased at higher temperature. 128 The O5 surface oxide reacted with CO, forming coexisting regions of surface oxide and metallic, CO-covered islands. Due to the low sticking probability of CO on the surface oxide, CO oxidation was limited to the boundary between these phases.…”

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confidence: 99%

“…The decomposition rate showed similar behavior as reported in ref. 128, with a slow initial rate followed by fast reduction. Starting from a reduced surface, the oxide vibrational signatures were not observed to develop under reaction conditions (w = 0.5, 60 hPa, and 525 K), not even after the surface switched to the state of higher activity.…”

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confidence: 99%

Surface science under reaction conditions: CO oxidation on Pt and Pd model catalysts

2017

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Platinum and palladium are frequently used as catalytic materials, for example for the oxidation of CO. This is one of the most widely studied reactions in the field of surface science. Although seemingly uncomplicated, it remains an active and interesting topic, which is partially explained by the push to conduct experiments on model systems under relevant reaction conditions. Recent developments in the surface-science methodology have allowed obtaining chemical and structural information on the active phase of model catalysts. Tools of the trade include near-ambient-pressure X-ray photoelectron spectroscopy, high-pressure scanning tunneling microscopy, high-pressure surface X-ray diffraction, and high-pressure vibrational spectroscopy. Interpretation is often aided by density functional theory in combination with thermodynamic and kinetic modeling. In this review, results for the catalytic oxidation of CO obtained by these techniques are compared. On several of the Pt and Pd surfaces, new structures develop in excess O 2 . For Pt, this requires a much larger excess of O 2 than for Pd. Most of these structures also develop in pure O 2 and are identified as (surface) oxides. A large body of evidence supports the conjecture that these oxides are more reactive than the corresponding O-covered metallic surfaces under similar conditions, although still debated in the literature. An outlook on this developing field, including directions that move away from CO oxidation towards more complex chemistry, concludes this review.

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Reduction behavior of oxidized Pd(100) and Pd75Ag25(100) surfaces using CO

Cited by 18 publications

References 87 publications

CO Oxidation on the Pd(111) Surface

CO Oxidation on the Pd(111) Surface

In‐Situ TEM on Epitaxial and Non‐Epitaxial Oxidation of Pd and Reduction of PdO at P = 0.2–0.7 bar and T = 20–650 °C

Surface science under reaction conditions: CO oxidation on Pt and Pd model catalysts

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