Growth of Ce on Rh(111)

Napetschnig, E.; Schmid, Michael; Варга, П.

doi:10.1016/j.susc.2004.03.006

Cited by 22 publications

(21 citation statements)

References 28 publications

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“…As previously reported [23][24][25]29] this indicates that a Ce-Rh alloy formation takes place already at room temperature. When the sample was exposed to increased doses of O 2 , the shift of the Rh 3d core level gradually decreased, and after an exposure of 50 L no shifts were observed for the Rh 3d core level compared to the clean Rh(110) substrate.…”

Section: Oxidation At Low O 2 Exposuresupporting

confidence: 85%

“…This indicates that CeO 2 is dominating in the topmost layers, while RhO x mainly forms a layer in between the CeO 2 layers at the top and the Rh (110) substrate. Still some intermixing can not be excluded and is to some degree excepted since it is observed earlier that Ce partly intermix with the Rh(110) substrate both at room temperature [23][24][25] and after annealing at 500°C [29]. Based on the present results the overlayer is expected to follow a gradient model where the concentration of RhO x increases with the depth of the overlayer.…”

Section: Oxidation At High O 2 Exposurementioning

confidence: 55%

“…The inelastic electron mean free path was estimated from the universal curve of the inelastic mean free path to be 10 Å for the Rh 3d levels. Since Ce and Rh exhibit some interaction already at room temperature [23][24][25], this estimate is rough and is mainly used to compare different thicknesses of Ce. Oxidation at doses up to 200 L was done in the main chamber with an oxygen pressure at 2.5 · 10 − 6 or 5.0 · 10 − 6 Pa, while oxidation at higher oxygen exposure than 200 L was performed in a reactor chamber connected to the main chamber.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Oxidation of thin Ce layers on Rh(110)

Juel¹,

Martinsen²,

Raaen³

2008

Thin Solid Films

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Section: Oxidation At Low O 2 Exposuresupporting

confidence: 85%

Section: Oxidation At High O 2 Exposurementioning

confidence: 55%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Oxidation of thin Ce layers on Rh(110)

Juel¹,

Martinsen²,

Raaen³

2008

Thin Solid Films

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“…In certain cases, neutralization effects can be too strong. This enhanced neutralization was experienced for Ce/Rh(111) 93 and to a certain extent on Ce/Cu(111), when Ne + was used. 58 In our extended LEIS experiments on the Rh/ceria system a Rh signal was not detected.…”

Section: Low-energy Ion Scattering (Leis) Experimentsmentioning

confidence: 94%

Probing the interaction of Rh, Co and bimetallic Rh–Co nanoparticles with the CeO₂ support: catalytic materials for alternative energy generation

Varga

Pusztai

Óvári³

et al. 2015

Phys. Chem. Chem. Phys.

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The interaction of CeO 2 -supported Rh, Co and bimetallic Rh-Co nanoparticles, which are active catalysts in hydrogen production via steam reforming of ethanol, a process related to renewable energy generation, was studied by X-ray diffraction (XRD), high resolution electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Furthermore, diffuse reflectance infrared spectroscopy (DRIFTS) of adsorbed CO as a probe molecule was used to characterize the morphology of metal particles. At small loadings (0.1%), Rh is in a much dispersed state on ceria, while at higher contents (1-5%), Rh forms 2-8 nm particles. Between 473-673 K pronounced oxygen transfer from ceria to Rh is observed and at 773 K significant agglomeration of Rh occurs. On reduced ceria, XPS indicates a possible electron transfer from Rh to ceria. The formation of smaller ceria crystallites upon loading with Co was concluded from XRD and HRTEM; for 10% Co, the CeO 2 particle size decreased from 27.6 to 10.7 nm. A strong dissolution of Co into ceria and a certain extent of encapsulation by ceria were deduced by XRD, XPS and LEIS. In the bimetallic system, the presence of Rh enhances the reduction of cobalt and ceria.During thermal treatments, reoxidation of Co occurs, and Rh agglomeration as well as oxygen migration from ceria to Rh are hindered in the presence of cobalt.

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“…For the clean (atomic oxygen treated surfaces) the independently quantified surface fractions add, within the experimental accuracy, up to about 100%. In exceptional situations where low-workfunction surfaces are investigated, such as by Napetschnig et al [35], matrix effects do occur and this is reflected in the sum of the apparent surface coverages being much lower than 100%. Even then, an accurate quantification of LEIS is still possible.…”

Section: Outermost Surface Characterization By Leismentioning

confidence: 99%

Surface active sites present in the orthorhombic M1 phases: low energy ion scattering study of methanol and allyl alcohol chemisorption over Mo–V–Te–Nb–O and Mo–V–O catalysts

et al. 2006

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The outermost surface compositions and chemical nature of active surface sites present on the orthorhombic (M1) Mo-V-O and Mo-V-Te-Nb-O phases were determined employing methanol and allyl alcohol chemisorption and surface reaction in combination with low energy ion scattering (LEIS). These orthorhombic phases exhibited vastly different behavior in propane (amm)oxidation reactions and, therefore, represented highly promising model systems for the study of the surface active sites. The LEIS data for the Mo-V-Te-Nb-O catalyst indicated surface depletion for V ()23%) and Mo ()27%), and enrichments for Nb (+55%) and Te (+165%) with respect to its bulk composition. Only minor changes in the topmost surface composition were observed for this catalyst under the conditions of the LEIS experiments at 400°C, which is a typical temperature employed in these propane transformation reactions. These findings strongly suggested that the bulk orthorhombic Mo-V-Te-Nb-O structure is terminated by a unique active and selective surface layer in propane (amm)oxidation. Moreover, direct evidence was obtained that the topmost surface VO x sites in the orthorhombic Mo-V-Te-Nb-O catalyst were preferentially covered by chemisorbed allyloxy species, whereas methanol was a significantly less discriminating probe molecule. The surface TeO x and NbO x sites on the Mo-V-Te-Nb-O catalyst were unable to chemisorb these probe molecules to the same extent as the VO x and MoO x sites. These findings suggested that vastly different catalytic behavior exhibited by the Mo-V-O and Mo-V-Te-Nb-O phases is related to different surface locations of V 5+ ions in the orthorhombic Mo-V-O and Mo-V-Te-Nb-O catalysts. Although the proposed isolated V 5+ pentagonal bipyramidal sites in the orthorhombic Mo-V-O phase may be capable of converting propane to propylene with modest selectivity, the selective 8-electron transformation of propane to acrylic acid and acrylonitrile may require the presence of several surface VO x redox sites lining the entrances to the hexagonal and heptagonal channels of the orthorhombic Mo-V-Te-Nb-O phase. Finally, the present study strongly indicated that chemical probe chemisorption combined with low energy ion scattering (LEIS) is a novel and highly promising surface characterization technique for the investigation of the active surface sites present in the bulk mixed metal oxides.

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Growth of Ce on Rh(111)

Cited by 22 publications

References 28 publications

Oxidation of thin Ce layers on Rh(110)

Oxidation of thin Ce layers on Rh(110)

Probing the interaction of Rh, Co and bimetallic Rh–Co nanoparticles with the CeO₂ support: catalytic materials for alternative energy generation

Surface active sites present in the orthorhombic M1 phases: low energy ion scattering study of methanol and allyl alcohol chemisorption over Mo–V–Te–Nb–O and Mo–V–O catalysts

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Growth of Ce on Rh(111)

Cited by 22 publications

References 28 publications

Oxidation of thin Ce layers on Rh(110)

Oxidation of thin Ce layers on Rh(110)

Probing the interaction of Rh, Co and bimetallic Rh–Co nanoparticles with the CeO2 support: catalytic materials for alternative energy generation

Surface active sites present in the orthorhombic M1 phases: low energy ion scattering study of methanol and allyl alcohol chemisorption over Mo–V–Te–Nb–O and Mo–V–O catalysts

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Probing the interaction of Rh, Co and bimetallic Rh–Co nanoparticles with the CeO₂ support: catalytic materials for alternative energy generation