Oxidation State of Ce in CeO2-Promoted Rh/Al2O3Catalysts during Methane Steam Reforming: H2O Activation and Alumina Stabilization

Duarte, Renata Bessa; Safonova, Оlga V.; Krumeich, Frank; Makosch, Martin; Bokhoven, Jeroen A. van

doi:10.1021/cs400207c

Cited by 47 publications

(49 citation statements)

References 60 publications

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“…5 In oxygendeficient oxides, cations in two oxidation states (3+ and 4+) are both present. 10 In heterogeneous catalysis, nanoparticles with a high surface area density are of great importance. 6 The oxygen storage capacity is essential for many applications of ceria based materials.…”

Section: Introductionmentioning

confidence: 99%

Quantitative depth profiling of Ce³⁺ in Pt/CeO₂ by in situ high-energy XPS in a hydrogen atmosphere

Kato

Ammann

Huthwelker

et al. 2015

Phys. Chem. Chem. Phys.

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The redox property of ceria is a key factor in the catalytic activity of ceria-based catalysts. The oxidation state of well-defined ceria nanocubes in gas environments was analysed in situ by a novel combination of near-ambient pressure X-ray Photoelectron Spectroscopy (XPS) and high-energy XPS at a synchrotron X-ray source. In situ high-energy XPS is a promising new tool to determine the electronic structure of matter under defined conditions. The aim was to quantitatively determine the degree of cerium reduction in a nano-structured ceria-supported platinum catalyst as a function of the gas environment. To obtain a non-destructive depth profile at near-ambient pressure, in situ high-energy XPS analysis was performed by varying the kinetic energy of photoelectrons from 1 to 5 keV, and, thus, the probing depth. In ceria nanocubes doped with platinum, oxygen vacancies formed only in the uppermost layers of ceria in an atmosphere of 1 mbar hydrogen and 403 K. For pristine ceria nanocubes, no change in the cerium oxidation state in various hydrogen or oxygen atmospheres was observed as a function of probing depth. In the absence of platinum, hydrogen does not dissociate and, thus, does not lead to reduction of ceria.

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Section: Introductionmentioning

confidence: 99%

Quantitative depth profiling of Ce³⁺ in Pt/CeO₂ by in situ high-energy XPS in a hydrogen atmosphere

Kato

Ammann

Huthwelker

et al. 2015

Phys. Chem. Chem. Phys.

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“… 60,61. In the former, the characteristic white line (indicated as C) corresponds to the 2p 2/3 → (4f 1 )5d electronic transition.…”

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confidence: 99%

Flame-Made WO₃/CeO_x-TiO₂ Catalysts for Selective Catalytic Reduction of NO_x by NH₃

et al. 2015

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Materials based on combination of tungsten-cerium-titanium are potentially durable catalysts for selective catalytic NO x reduction using NH 3 (NH 3 -SCR). Flame spray synthesis is used here to produce WO 3 /CeO x -TiO 2 nanoparticles, which are characterized with respect to their phase composition, morphology and acidic properties and are evaluated for deNO x by NH 3 -SCR. HR-TEM and XRD revealed that flame-made WO 3 /CeO x -TiO 2 consists of mainly rutile TiO 2 , brannerite CeTi 2 O 6 , cubic CeO 2 and a minor fraction of anatase TiO 2 . These phases coexist with a large portion of amorphous mixed Ce-Ti phase. The lack of crystallinity and the presence of brannerite together with the evident high fraction of Ce 3+ are taken as evidence that cerium is also present as a dopant in TiO 2 and is well dispersed on the surface of the nano-particles. Clusters of amorphous WO 3 homogeneously cover all particles as observed by STEM. Such morphology and phase composition guarantee short range Ce-O-Ti and Ce-O-W interactions and thus the high surface concentration of Ce 3+ . The presence of the WO 3 layer and the close Ce-O-W interaction further increase the Ce 3+ content compared to binary Ce-Ti materials as shown by XPS and XANES. The acidity of the materials and the nature of the acid sites were determined by NH 3 temperature programmed desorption (NH 3 -TPD) and DRIFT spectroscopy, respectively. TiO 2 possesses mainly strong Lewis acidity; addition of cerium, especially the presence of surface Ce 3+ in close contact with titanium and tungsten, inducesBrønsted acid sites that are considerably increased by the amorphous WO 3 clusters. As a result of this peculiar element arrangement and phase composition, 10 wt% WO 3 /10 mol% CeO x -90 mol% TiO 2 exhibits the highest deNO x efficiency, which matches that of a V 2 O 5 -WO 3 /TiO 2 catalyst. Preliminary activity data indicate that the flame-made catalyst demonstrates much higher performance after thermal and hydrothermal aging at 700°C than the V-based analogue despite the presence of the rutile phase. Ce 3+ remains the dominating surface cerium species after both aging treatments thus confirming its crucial role in NH 3 -SCR by Ce-W-Ti based catalysts.

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“…Besides as catalyst, ceria (CeO 2 ) prevents alumina from sintering and stabilizes supported nano-sized precious metals such as rhodium, palladium and platinum, which are very important for the enhancement of TWCs activity. 15 Rh/γ-Al 2 O 3 -CeO 2 system had been also investigated as catalyst for the methane steam reforming 16 and the oxidation of methyl tert-butyl ether. 11 In particular, γ-Al 2 O 3 is often used as a support of ceria and noble metals since compared to the other aluminum oxides it features higher catalytic activity due to its structural characteristics and its acid-base properties.…”

Section: Introductionmentioning

confidence: 99%

“…[6][7][8] Alumina is a basic component of TWCs and it is widely used in heterogeneous catalysis 9,10 as a support in the refining and petrochemical industries. 17 Shi 18 For Rh/CeO 2 /Al 2 O 3 catalytic system Duarte et al 16 recently reported that, when a reduced sample containing a significant fraction of Ce 3+ ions is exposed to oxygen only part of the Ce 3+ species are converted to Ce 4+ , while a substantial amount of cerium ions remains in oxidation state +3. 12,13,14 CeO 2 /γ-Al 2 O 3 catalysts are also efficient for the dehydrogenation of ethane to ethylene.…”

Section: Introductionmentioning

confidence: 99%

“…11 In particular, γ-Al 2 O 3 is often used as a support of ceria and noble metals since compared to the other aluminum oxides it features higher catalytic activity due to its structural characteristics and its acid-base properties. 16 Moreover, under reaction conditions, a significant fraction of cerium was reduced. 15 Rh/γ-Al 2 O 3 -CeO 2 system had been also investigated as catalyst for the methane steam reforming 16 and the oxidation of methyl tert-butyl ether.…”

Section: Introductionmentioning

confidence: 99%

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Relative stability and reducibility of CeO₂ and Rh/CeO₂ species on the surface and in the cavities of γ-Al₂O₃: a periodic DFT study

Koleva

Aleksandrov

Vayssilov

et al. 2015

Phys. Chem. Chem. Phys.

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We report the structure and stability of ceria units deposited on the surface of γ-Al2O3 or incorporated in its cavities, as determined by periodic density functional calculations. Ceria species are modeled as CeO2 or Ce2O4 moieties or as a small nanoparticle, Ce13O26, on the (100) and (001) surfaces of a γ-Al2O3 slab. Among the studied structures the incorporation of Ce(4+) ions in cavities of γ-Al2O3 is favored with respect to the ions on the surface only in subsurface cavities of the (100) surface. The calculations also suggested that formation of a surface layer of ceria on the (100) alumina surface is preferable compared to three-dimensional moieties. The deposition of a small ceria nanoparticle on (100) and (001) surfaces of γ-Al2O3 reduces the energy for oxygen vacancy formation to an essentially spontaneous process on the (100) surface, which may be the reason for the experimentally detected large fraction of Ce(3+) ions in the CeO2/γ-Al2O3 systems. The deposition of a single rhodium atom or RhO unit in some of the structures with a CeO2 unit and Ce13O26 showed that spontaneous electron transfer from rhodium to cerium ion occurs, which results in reduction of Ce(4+) to Ce(3+) and the oxidation of rhodium. Only in the presence of deposited rhodium atoms, the incorporated cerium ions can be reduced to Ce(3+).

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Oxidation State of Ce in CeO₂-Promoted Rh/Al₂O₃Catalysts during Methane Steam Reforming: H₂O Activation and Alumina Stabilization

Cited by 47 publications

References 60 publications

Quantitative depth profiling of Ce³⁺ in Pt/CeO₂ by in situ high-energy XPS in a hydrogen atmosphere

Quantitative depth profiling of Ce³⁺ in Pt/CeO₂ by in situ high-energy XPS in a hydrogen atmosphere

Flame-Made WO₃/CeO_x-TiO₂ Catalysts for Selective Catalytic Reduction of NO_x by NH₃

Relative stability and reducibility of CeO₂ and Rh/CeO₂ species on the surface and in the cavities of γ-Al₂O₃: a periodic DFT study

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Oxidation State of Ce in CeO2-Promoted Rh/Al2O3Catalysts during Methane Steam Reforming: H2O Activation and Alumina Stabilization

Cited by 47 publications

References 60 publications

Quantitative depth profiling of Ce3+ in Pt/CeO2 by in situ high-energy XPS in a hydrogen atmosphere

Quantitative depth profiling of Ce3+ in Pt/CeO2 by in situ high-energy XPS in a hydrogen atmosphere

Flame-Made WO3/CeOx-TiO2 Catalysts for Selective Catalytic Reduction of NOx by NH3

Relative stability and reducibility of CeO2 and Rh/CeO2 species on the surface and in the cavities of γ-Al2O3: a periodic DFT study

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Oxidation State of Ce in CeO₂-Promoted Rh/Al₂O₃Catalysts during Methane Steam Reforming: H₂O Activation and Alumina Stabilization

Quantitative depth profiling of Ce³⁺ in Pt/CeO₂ by in situ high-energy XPS in a hydrogen atmosphere

Quantitative depth profiling of Ce³⁺ in Pt/CeO₂ by in situ high-energy XPS in a hydrogen atmosphere

Flame-Made WO₃/CeO_x-TiO₂ Catalysts for Selective Catalytic Reduction of NO_x by NH₃

Relative stability and reducibility of CeO₂ and Rh/CeO₂ species on the surface and in the cavities of γ-Al₂O₃: a periodic DFT study