Copper-ceria interaction: A combined photoemission and DFT study

Szabová, Lucie; Škála, Tomáš; Matolı́nová, Iva; Fabris, Stefano; Camellone, Matteo Farnesi; Matolín, Vladimı́r

doi:10.1016/j.apsusc.2012.04.098

Cited by 38 publications

(62 citation statements)

References 32 publications

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“…This interpretation is consistent with the results of Matolin et al 18 shown in Figure 6, whereby Cu reduced stoichiometric CeO 2 (111), but initially oxidized the heavily reduced CeO 1.73 (111) surface. Because Cu adsorbs mainly at step edges at very low coverage on CeO 1.73 (111), Cu is mainly binding to oxygen vacancies, where DFT predicts that it will gain electron density from ceria.…”

Section: Articlesupporting

confidence: 92%

Energetics of Cu Adsorption and Adhesion onto Reduced CeO₂(111) Surfaces by Calorimetry

et al. 2015

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The morphology and interfacial energetics of vapor-deposited Cu on slightly reduced CeO 2 (111) surfaces at 300 K have been studied using single crystal adsorption calorimetry (SCAC), He + low-energy ion scattering spectroscopy (ISS), Xray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). Copper grows as three-dimensional nanoparticles with a density of ∼10 13 particles/cm 2 on CeO 2−x (111) (x = 0.05, 0.1, and 0.2). The initial heat of adsorption of Cu decreased with the extent of reduction, showing that stoichiometric ceria adsorbs Cu more strongly than oxygen vacancies. On CeO 1.95 (111), the heat dropped quickly with coverage in the first 0.1 ML, attributed to nucleation of Cu clusters on stoichiometric steps, followed by the Cu particles spreading onto less favorable sites (step vacancies and terraces). Above ∼0.1 ML (>0.8 nm in diameter), the Cu adsorption energies showed no variation with extent of ceria reduction: the heat of adsorption increased slowly with coverage (particle size) due to the formation of more Cu−Cu bonds per adatom as the size grows, finally approaching the heat of sublimation of bulk Cu by 3.5 ML (2.5 nm). The adhesion energy of Cu(solid) to CeO 1.95 (111) was found to be 3.52 J/m 2 for 2.2 nm diameter particles, decreasing slightly with the extent of reduction. The Ce 3d XPS line shape showed an increase in the Ce 3+ /Ce 4+ ratio with Cu coverage, corresponding to donation of at most ∼0.17 and 0.06 electrons per Cu atom to CeO 1.95 (111) and CeO 1.8 (111), respectively. INTRODUCTIONHeterogeneous catalysts are generally composed of late transition metal nanoparticles dispersed over high surface area oxide supports. The interaction of the supported metal and underlying oxide can greatly influence catalytic properties such as long-term sinter resistance, activity, and selectivity. To improve our understanding of how the choice of metal and support can influence catalytic properties, detailed studies of model systems, where metal atoms are vapor deposited onto single crystal oxide supports, are often employed. With these model systems, the structure of the support surface, the size of the metal particles, and surface cleanliness can be better controlled. 1−5 Studies of this type provide the basic understanding necessary for the intelligent design of new, more efficient, and greener catalysts. Here we apply that approach to study model Cu/CeO 2 catalysts consisting of Cu nanoparticles grown by vapor deposition on CeO 2 (111) surfaces with controlled extents of reduction.We study the energies of the Cu atoms in this system using single crystal adsorption calorimetry (SCAC). This method directly measures the adsorption energy of the incoming metal atoms as they bind to the oxide surface, and to metal nanoparticles on that surface as they grow in size. 6−11 The Cu nanoparticle morphology is characterized using ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS). Adsorption energies measured using SCAC along with detailed adsorbate structura...

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Section: Articlesupporting

confidence: 92%

Energetics of Cu Adsorption and Adhesion onto Reduced CeO₂(111) Surfaces by Calorimetry

et al. 2015

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“…Using the PBE + 4.5 functional, the calculated charge transfer is greater than PBE +5; however, PW91 gives a similar extent of charge transfer independent of U value. Our XPS results 29 and RPES results from Matolin et al 24 indicate only a small amount of electron density is transferred from Cu to CeO 2 (111), less than 0.17 electrons per Cu atom at 1.2 ML Cu coverage 29 . It thus seems that all these DFT functionals are overestimating the extent of charge transfer, although the charge transfer per Cu atom is not known from experiments at the very low coverage and temperature required to maintain isolated Cu adatoms.…”

Section: Discussionmentioning

confidence: 65%

Energy of Supported Metal Catalysts: From Single Atoms to Large Metal Nanoparticles

2015

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Many catalysts consist of late transition metal nanoparticles dispersed across oxide supports. The chemical potential of the metal atoms in these particles correlate with their catalytic activity and long-term thermal stability. This chemical potential versus particle size, across the full size range between the single isolated atom and bulk-like limits, is reported here for the first time for any metal on any oxide. The chemical potential of Cu atoms on CeO 2 (111) surfaces, determined by single crystal adsorption calorimetry (SCAC) of gaseous Cu atoms onto slightly-reduced CeO 2 (111) at 100 and 300 K, is shown to decrease dramatically with increasing Cu cluster size. The Cu chemical potential is ~110 kJ/mol higher for isolated Cu adatoms on stoichometric terrace sites than for Cu in nanoparticles exceeding 2.5 nm diameter, where it reaches the bulk Cu(solid) limit. In Cu dimers, Cu's chemical potential is ~57 kJ/mol lower at step edges than on stoichiometric terrace sites. Since Cu avoids oxygen vacancies, these monomer and dimer results are not strongly influenced by the 2.5% oxygen vacancies present on this CeO 2 surface, and are thus considered representative of stoichiometric CeO 2 (111) surfaces.

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“…This behavior suggests that Rh deposition induces reduction of cerium oxide on sample (A) and re-oxidation of cerium oxide on sample (B). Reduction of ceria by deposited metal has been reported earlier for Pt/CeO 2 [6], Pd/CeO 2 [20,21], Au/CeO 2 [22], and Cu/CeO 2 [24] systems. The extent of ceria reduction induced by these metals is comparable to that observed on Rh/CeO x (A) sample.…”

Section: Results and Discussion 31 Electronic Metal Support Interacmentioning

confidence: 85%

“…This assumption complies with the DFT calculations of Yang et al [41], who predicted formation of the gap states (mixed Rh 4d with O 2p) capable of accommodation of the electrons left upon removal of oxygen from cerium oxide. Therefore, the observed re-oxidation of reduced cerium oxide might be caused by a charge transfer from the support to the Rh particles similar to Au/TiO 2 (110) [18,19] and Cu/CeO 2 [24] systems. The difference between two samples (A) and (B) is also apparent from the development of Rh 3d 5/2 core levels ( Figure S1).…”

Section: Results and Discussion 31 Electronic Metal Support Interacmentioning

confidence: 93%

“…In contrast, charge transfer from the support to the metal particles leads to re-oxidation of titanium oxide and negative net charge on Au particles supported on reduced TiO 2-x (110). The charge transfer from the metal particles to the support has been also identified in several systems containing metal particles supported on well-ordered stoichiometric CeO 2 (111) films: Pt/CeO 2 [6,16], Pd/CeO 2 [20,21], Au/CeO 2 [22], Ag/CeO 2 [23], and Cu/CeO 2 [24]. However, fewer studies exist on the effects of metal deposition on reduced CeO 2-x surfaces [24].…”

Section: Introductionmentioning

confidence: 95%

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Impact of Rh–CeO interaction on CO oxidation mechanisms

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Copper-ceria interaction: A combined photoemission and DFT study

Cited by 38 publications

References 32 publications

Energetics of Cu Adsorption and Adhesion onto Reduced CeO₂(111) Surfaces by Calorimetry

Energetics of Cu Adsorption and Adhesion onto Reduced CeO₂(111) Surfaces by Calorimetry

Energy of Supported Metal Catalysts: From Single Atoms to Large Metal Nanoparticles

Impact of Rh–CeO interaction on CO oxidation mechanisms

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Copper-ceria interaction: A combined photoemission and DFT study

Cited by 38 publications

References 32 publications

Energetics of Cu Adsorption and Adhesion onto Reduced CeO2(111) Surfaces by Calorimetry

Energetics of Cu Adsorption and Adhesion onto Reduced CeO2(111) Surfaces by Calorimetry

Energy of Supported Metal Catalysts: From Single Atoms to Large Metal Nanoparticles

Impact of Rh–CeO interaction on CO oxidation mechanisms

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Energetics of Cu Adsorption and Adhesion onto Reduced CeO₂(111) Surfaces by Calorimetry

Energetics of Cu Adsorption and Adhesion onto Reduced CeO₂(111) Surfaces by Calorimetry