Surface investigation on CexZr1-xO2 compounds

Daturi, Marco; Binet, Claude; Lavalley, Jean‐Claude; Galtayries, Anouk; Sporken, R.

doi:10.1039/a905758g

Cited by 157 publications

(139 citation statements)

References 29 publications

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“…Indeed, several experimental studies have presented comparisons of the bulk and surface compositions in ceria-zirconia samples, but the results are somewhat contradictory. For example, Daturi et al (1999), using both X-ray photoelectron spectroscopy (XPS) and the band intensities of adsorbed methoxy species, found no evidence of surface segregation in ceria-zirconia samples in the full range of compositions, while Bozo et al (2001), using XPS and ion scattering spectroscopy, found that phase separation at high temperatures occurred with Zr enrichment at the surface. However, a number of other experimental studies have found Ce enrichment at the surface of the solid solution, in agreement with our theoretical prediction.…”

Section: (B) Cation Segregation At the (111) Surfacementioning

confidence: 99%

“…For example, the samples in the work by Daturi et al (1999) were treated with temperatures (873 K) that were not high enough to allow cation diffusion and redistribution, which possibly explains the absence of cation segregation in their samples. The observation of a Zr-rich surface by Bozo et al (2001) is more intriguing, and suggests that other factors, including kinetic ones, or opposite segregation behaviour of other surfaces in the solution, could be present, which requires further investigation.…”

Section: (B) Cation Segregation At the (111) Surfacementioning

confidence: 99%

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Phase separation and surface segregation in ceria–zirconia solid solutions

et al. 2011

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Using a combination of density functional theory calculations and statistical mechanics, we show that a wide range of intermediate compositions of ceria-zirconia solid solutions are thermodynamically metastable with respect to phase separation into Ce-rich and Zr-rich oxides. We estimate that the maximum equilibrium concentration of Zr in CeO 2 at 1373 K is approximately 2 per cent, and therefore, equilibrated samples with higher Zr content are expected to exhibit heterogeneity at the atomic scale. We also demonstrate that in the vicinity of the (111) surface, cation redistribution at high temperatures will occur with significant Ce enrichment of the surface, which we attribute to the more covalent character of Zr-O bonds compared with Ce-O bonds. Although the kinetic barriers for cation diffusion normally prevent the decomposition/segregation of ceria-zirconia solid solutions in typical catalytic applications, the separation behaviour described here can be expected to occur in modern three-way catalytic converters, where very high temperatures are reached.

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Section: (B) Cation Segregation At the (111) Surfacementioning

confidence: 99%

Section: (B) Cation Segregation At the (111) Surfacementioning

confidence: 99%

Phase separation and surface segregation in ceria–zirconia solid solutions

et al. 2011

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“…This amount is practically the same for both samples and can be due, probably, to a photoreduction process of ceria during XPS experiment [42,43,46,47]. Nevertheless, the reduction treatment at 473 K leads to different behavior in the catalysts.…”

Section: Icp-oesmentioning

confidence: 74%

Effect of the metal precursor on the properties of Pt/CeO2/C catalysts for the total oxidation of ethanol

et al. 2015

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. Toluene hydrogenation has been used to obtain an estimation of the platinum dispersion on the investigated catalysts. On the other hand, their catalytic behavior has been evaluated in the total oxidation of ethanol, selected as a VOCs probe molecule. A much higher catalytic activity and selectivity to CO2 was achieved with chlorinated catalysts. This behavior has been correlated with a high platinum dispersion and a strong metal-CeO2 interaction in these catalysts which promotes their redox properties. This is a previous version of the article published in Catalysis Today. 2015Today. , 249: 109-116. doi:10.1016Today. /j.cattod.2014 Highlights -Highly efficient catalysts for the complete oxidation of ethanol have been developed.-The use of CeO 2 as promoter is optimized by dispersing it over the activated carbon surface.-Impact of the platinum precursor (chlorinated or Cl-free) on the catalytic activity.-Pt/CeO 2 /C catalysts are more active than Pt/CeO 2 . K, ICP, XRD, H 2 -TPR and XPS). Toluene hydrogenation has been used to obtain an estimation of the platinum dispersion on the investigated catalysts. On the other hand, their catalytic behavior has been evaluated in the total oxidation of ethanol, selected as a VOCs probe molecule. A much higher catalytic activity and selectivity to CO 2 was achieved with chlorinated catalysts. This behavior has been correlated with a high platinum dispersion and a strong metal-CeO 2 interaction in these catalysts which promotes their redox properties.

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“…18,20,30,32,34 The other two contributions are due to CO adsorbed on the support. They correspond to molecular forms weakly interacting with the CZ surface cations, whose characteristic¯-CO stretching bands are observed above 2143 cm ¹1 , 52,53 and to carbonate-like species resulting from the strong interaction of CO with the surface anions of the support, respectively. The features characterizing the latter species appear at much lower wavenumbers, typically below 1700 cm ¹1 .…”

Section: ç 2 Quantitative Estimate Of Metal Andmentioning

confidence: 99%

“…The features characterizing the latter species appear at much lower wavenumbers, typically below 1700 cm ¹1 . 52,53 It is, therefore, critically important to develop an experimental approach allowing us to separate the three contributions above.…”

Section: ç 2 Quantitative Estimate Of Metal Andmentioning

confidence: 99%

Recent Progress in Chemical Characterization of Supported Gold Catalysts: CO Adsorption on Au/Ceria–Zirconia

et al. 2011

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An approach correlating quantitative CO adsorption data with the nanostructural properties of Au/CeO 2 ZrO 2 catalysts is discussed. It has been used to show that the CO adsorption occurs on Au sites with coordination number¯7, that Au dispersion has a dramatic influence on the amount of CO strongly chemisorbed on the support, and that a fully reversible SMSI effect may be induced by successive mild reduction and reoxidation treatments. Ç 1. IntroductionThe discovery in 1987 by Haruta et al.1 that gold highly dispersed on appropriate oxide supports shows much higher CO oxidation activity than the analogous systems constituted by noble metals of Groups 810 represents a major breakthrough point in the history of the catalysis by gold.2 Following this, in principle, unexpected finding, 3 a dramatic increase in the number of published papers on gold catalysts has been observed. 4 Despite the big research effort devoted to this topic, many important questions about the ultimate origin of the exceptional behavior of gold remain open to discussion. 5The adsorption of the reactant molecules is acknowledged to be a key initial step of the heterogeneous catalytic processes. Accordingly, to gain detailed information about the surface chemistry of gold is certainly a relevant issue in order to arrive at a finer understanding of its catalytic behavior. As recently stressed, 2 until some 20 years ago, very little information was available on the chemisorptive properties of gold, the extreme nobility which was traditionally assumed to characterize this metal being invoked to justify this lack of studies. In the last two decades, however, the number of papers dealing with this topic has grown very rapidly, 2,6 a considerable amount of data being presently available. Though the adsorption of a relatively large number of molecules and atoms has been investigated, 6 CO is certainly one of the most commonly used probe molecules for gold surfaces. At present, the COAu interaction has been investigated on a variety of systems including massive single crystals, 612 small clusters or nanoparticles supported on both planar model, 1324 and powdered oxides.2534 Studies on the CO interaction with gas-phase Au clusters have also been reported. 3537 Depending on the specificities of the investigated systems, significantly different experimental conditions and techniques have been applied in the above-mentioned studies. Finally, CO adsorption on gold has also been investigated from a theoretical point of view. 1416,38,39 From all these studies a number of relevant conclusions have already been obtained. Thus, with reference to the noble metals of Groups 810, gold interaction with CO is much weaker.2,6 Consistently, it is generally acknowledged that the active sites for CO adsorption consist of defective, lowcoordination, surface gold atoms. 2,6,22,40 This represents a first problem very much limiting the conventional use of CO as a tool for characterizing gold surfaces. In the case of supported gold catalysts, the simultaneous occ...

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Surface investigation on CexZr1-xO2 compounds

Cited by 157 publications

References 29 publications

Phase separation and surface segregation in ceria–zirconia solid solutions

Phase separation and surface segregation in ceria–zirconia solid solutions

Effect of the metal precursor on the properties of Pt/CeO2/C catalysts for the total oxidation of ethanol

Recent Progress in Chemical Characterization of Supported Gold Catalysts: CO Adsorption on Au/Ceria–Zirconia

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