The oxidation state and catalytic activity of supported rhodium

Oh, Seung Kyo

doi:10.1016/0021-9517(83)90274-9

Cited by 75 publications

(23 citation statements)

References 5 publications

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“…1 Also, a supported Rh/Al 2 O 3 catalyst was found to be less active in the oxidized than in the reduced state in the CO/NO conversion reaction. 2 The interaction of oxygen and noble metal surfaces has been investigated extensively during latter years. For example, in the case of a Rh(111) single crystal oxidized in 1 Torr of O 2 at <800 K, an epitaxial RhO phase was observed based on low-energy electron diffraction (LEED) and AES measurements.…”

Section: Introductionmentioning

confidence: 99%

High‐temperature‐aging‐promoted Rh oxides on supported automotive exhaust catalysts

Suhonen¹,

Hietikko²,

Polvinen³

et al. 2002

Surface & Interface Analysis

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Thermal decomposition of noble metal oxide phases formed during aging in air on industrially manufactured g-Al 2 O 3 -supported Rh catalysts was investigated. Some of the catalyst washcoats were modified by various stabilizers, promoters and oxygen storage components, such as La 2 O 3 , CeO 2 and Ce-Zr mixed oxide. In order to investigate the effect of aging, stabilizers and manufacturing method on the thermal stability of the noble metal oxide phases formed, a stepwise thermal decomposition in high vacuum (pressure <10 −7 Torr) was performed. X-ray photoelectron spectroscopy (XPS) was used to observe the changes in chemical state after each annealing cycle. Our results show marked differences in the rate of reduction between different Rh catalysts. Disposition of the Rh oxides towards reduction was also investigated by exposing the catalysts to 400 mbar of H 2 at 300 • C for 30 min. After 3 h of aging in air at 1000• C an irreducible rhodium oxide, which was identified to be either Rh 2 O 3 diffused into alumina or RhO 2 in intimate contact with the alumina surface, was formed regardless of the Ce-Zr mixed-oxide additive and manufacturing method of the catalyst.

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Section: Introductionmentioning

confidence: 99%

High‐temperature‐aging‐promoted Rh oxides on supported automotive exhaust catalysts

Suhonen¹,

Hietikko²,

Polvinen³

et al. 2002

Surface & Interface Analysis

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show abstract

“…Lacking microscopic in-situ data to really resolve this issue a possibly beneficial role has e.g. been suspected for PdO at Pd 7 , whereas Rhodium oxides have predominantly been viewed as poisoning the catalytic reaction 2,3,4 .…”

Section: Introductionmentioning

confidence: 99%

“…refs. 2,3,4,5,6,7,8), with oxide formation at the surface of the metal particles potentially having either beneficial or detrimental effects on the overall activity. Lacking microscopic in-situ data to really resolve this issue a possibly beneficial role has e.g.…”

Section: Introductionmentioning

confidence: 99%

Oxide formation at the surface of late 4d transition metals: insights from first-principles atomistic thermodynamics

2004

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Using density-functional theory we assess the stability of bulk and surface oxides of the late 4d transition metals in a "constrained equilibrium" with a gas phase formed of O2 and CO. While the stability range of the most stable bulk oxide extends for ruthenium well into gas phase conditions representative of technological CO oxidation catalysis, this is progressively less so for the 4d metals to its right in the periodic system. Surface oxides could nevertheless still be stable under such conditions. These thermodynamic considerations are discussed in the light of recent experiments, emphasizing the role of (surface) oxides as the active phase of model catalysts formed from these metals.

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“…In particular, for applications such as the CO oxidation on transition metal based catalysts, oxide formation at the catalyst's surface in the reactive environment was primarily viewed as leading to an inactive surface oxide poisoning the catalytic reaction, as e.g. in the case of Rh surfaces, [1][2][3] while recent experiments showed that the high catalytic activity of the Ru(0001) surface with respect to the CO oxidation relates in fact to the existence of RuO 2 (110) oxide patches that form under oxidizing conditions. [4][5][6] Thus, apparently, unreactive surface oxides are more likely to form on Rh than on Ru surfaces.…”

Section: Introductionmentioning

confidence: 99%

Stability of subsurface oxygen at Rh(111)

2002

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Using density-functional theory (DFT) we investigate the incorporation of oxygen directly below the Rh(111) surface. We show that oxygen incorporation will only commence after nearly completion of a dense O adlayer (θtot ≈ 1.0 monolayer) with O in the fcc on-surface sites. The experimentally suggested octahedral sub-surface site occupancy, inducing a site-switch of the onsurface species from fcc to hcp sites, is indeed found to be a rather low energy structure. Our results indicate that at even higher coverages oxygen incorporation is followed by oxygen agglomeration in two-dimensional sub-surface islands directly below the first metal layer. Inside these islands, the metastable hcp/octahedral (on-surface/sub-surface) site combination will undergo a barrierless displacement, introducing a stacking fault of the first metal layer with respect to the underlying substrate and leading to a stable fcc/tetrahedral site occupation. We suggest that these elementary steps, namely, oxygen incorporation, aggregation into sub-surface islands and destabilization of the metal surface may be more general and precede the formation of a surface oxide at close-packed late transition metal surfaces.

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The oxidation state and catalytic activity of supported rhodium

Cited by 75 publications

References 5 publications

High‐temperature‐aging‐promoted Rh oxides on supported automotive exhaust catalysts

High‐temperature‐aging‐promoted Rh oxides on supported automotive exhaust catalysts

Oxide formation at the surface of late 4d transition metals: insights from first-principles atomistic thermodynamics

Stability of subsurface oxygen at Rh(111)

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