Characterization of Rh, Mo and Rh-Mo particles formed on TiO 2(110) surface: A TDS, AES and RAIRS study

L. Bugyi, Róbert Németh

Research output: Contribution to journalArticle

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Abstract

The structural and chemical characterization of Rh, Mo and Rh-Mo nanosized clusters formed by physical vapor deposition on TiO2 single crystal was performed by Auger Electron Spectroscopy (AES), Thermal Desorption Spectroscopy (TDS) and Reflection Absorption Infrared Spectroscopy (RAIRS), applying CO as test molecule. On a slightly reduced titania surface 2D-like growth of Rh was revealed at 300 K up to 0.23 ML coverage by AES and CO-desorption experiments. For CO-saturated Rh particles TDS showed molecular CO desorption in a broad temperature range with Tp = 400, 440, 490 and 540 K (α-states), the latter state appearing only on the smallest Rh particles. The population of γ-state (Tp = 780-820 K) originating from the recombination of C and O atoms on the support began at ΘRh = 0.23ML and was maximized at around 1-2 ML Rh coverage, corresponding to 30% dissociation of CO. A possible dissociation precursor on Rh particles is identified as linearly bonded CO on step sites characterized by ν(C-O) of 2017 cm- 1. Deliberation of CO2 could not be detected between 170 and 900 K, showing the absence of disproportionation reaction. Instead of oxidizing CO molecules, oxygen atoms stemming from the dissociation of CO attached to the reduced centers of titania, indicating the role of adsorption sites at the perimeter of Rh particles in the decomposition process. 2 ML of predeposited Mo enhanced markedly the dispersion of Rh particles as a result of strong Rh-Mo interaction, but it slightly reduced the molecular α-CO desorption possibly due to enhanced dissociation. The formation of γ-CO was suppressed considerably through elimination of adsorption centers by Mo on the TiO2 substrate. The reactivity of Rh layers deposited on Mo-covered surface towards CO was reduced after repeated annealing to 600 K due to partial encapsulation of Rh by titania, manifesting in the suppression of the more strongly bonded α-state. Mo-deposits (up to 0.5ML) on Rh particles decreased the saturation coverage of α-CO through a site-blocking mechanism without detectable influence on the binding energy of CO to Rh, indicating Mo island formation. The carbon arising from the decomposition of CO dissolved in the Mo-containing particles formed a solid solution stable even at 900 K, suggesting a possible role of molybdenum carbide regarding the enhanced catalytic activity of Rh clusters.

Original languageEnglish
Pages (from-to)808-817
Number of pages10
JournalSurface Science
Volume605
Issue number7-8
DOIs
Publication statusPublished - Apr 2011

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Electron reflection
Thermal desorption spectroscopy
Auger electron spectroscopy
Carbon Monoxide
Absorption spectroscopy
Auger spectroscopy
electron spectroscopy
Infrared spectroscopy
absorption spectroscopy
desorption
infrared spectroscopy
Desorption
Titanium
spectroscopy
dissociation
Decomposition
titanium
Adsorption
Atoms
Molecules

Keywords

  • Carbon deposit
  • Carbon monoxide
  • Dissociation precursor
  • Encapsulation
  • Mo-Rh nanoparticles
  • Perimeter sites
  • Reduced titania support
  • Site-blocking

ASJC Scopus subject areas

  • Surfaces and Interfaces
  • Condensed Matter Physics
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

Characterization of Rh, Mo and Rh-Mo particles formed on TiO 2(110) surface : A TDS, AES and RAIRS study. / Bugyi, L.; Németh, Róbert.

In: Surface Science, Vol. 605, No. 7-8, 04.2011, p. 808-817.

Research output: Contribution to journalArticle

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abstract = "The structural and chemical characterization of Rh, Mo and Rh-Mo nanosized clusters formed by physical vapor deposition on TiO2 single crystal was performed by Auger Electron Spectroscopy (AES), Thermal Desorption Spectroscopy (TDS) and Reflection Absorption Infrared Spectroscopy (RAIRS), applying CO as test molecule. On a slightly reduced titania surface 2D-like growth of Rh was revealed at 300 K up to 0.23 ML coverage by AES and CO-desorption experiments. For CO-saturated Rh particles TDS showed molecular CO desorption in a broad temperature range with Tp = 400, 440, 490 and 540 K (α-states), the latter state appearing only on the smallest Rh particles. The population of γ-state (Tp = 780-820 K) originating from the recombination of C and O atoms on the support began at ΘRh = 0.23ML and was maximized at around 1-2 ML Rh coverage, corresponding to 30{\%} dissociation of CO. A possible dissociation precursor on Rh particles is identified as linearly bonded CO on step sites characterized by ν(C-O) of 2017 cm- 1. Deliberation of CO2 could not be detected between 170 and 900 K, showing the absence of disproportionation reaction. Instead of oxidizing CO molecules, oxygen atoms stemming from the dissociation of CO attached to the reduced centers of titania, indicating the role of adsorption sites at the perimeter of Rh particles in the decomposition process. 2 ML of predeposited Mo enhanced markedly the dispersion of Rh particles as a result of strong Rh-Mo interaction, but it slightly reduced the molecular α-CO desorption possibly due to enhanced dissociation. The formation of γ-CO was suppressed considerably through elimination of adsorption centers by Mo on the TiO2 substrate. The reactivity of Rh layers deposited on Mo-covered surface towards CO was reduced after repeated annealing to 600 K due to partial encapsulation of Rh by titania, manifesting in the suppression of the more strongly bonded α-state. Mo-deposits (up to 0.5ML) on Rh particles decreased the saturation coverage of α-CO through a site-blocking mechanism without detectable influence on the binding energy of CO to Rh, indicating Mo island formation. The carbon arising from the decomposition of CO dissolved in the Mo-containing particles formed a solid solution stable even at 900 K, suggesting a possible role of molybdenum carbide regarding the enhanced catalytic activity of Rh clusters.",
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T1 - Characterization of Rh, Mo and Rh-Mo particles formed on TiO 2(110) surface

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AU - Bugyi, L.

AU - Németh, Róbert

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N2 - The structural and chemical characterization of Rh, Mo and Rh-Mo nanosized clusters formed by physical vapor deposition on TiO2 single crystal was performed by Auger Electron Spectroscopy (AES), Thermal Desorption Spectroscopy (TDS) and Reflection Absorption Infrared Spectroscopy (RAIRS), applying CO as test molecule. On a slightly reduced titania surface 2D-like growth of Rh was revealed at 300 K up to 0.23 ML coverage by AES and CO-desorption experiments. For CO-saturated Rh particles TDS showed molecular CO desorption in a broad temperature range with Tp = 400, 440, 490 and 540 K (α-states), the latter state appearing only on the smallest Rh particles. The population of γ-state (Tp = 780-820 K) originating from the recombination of C and O atoms on the support began at ΘRh = 0.23ML and was maximized at around 1-2 ML Rh coverage, corresponding to 30% dissociation of CO. A possible dissociation precursor on Rh particles is identified as linearly bonded CO on step sites characterized by ν(C-O) of 2017 cm- 1. Deliberation of CO2 could not be detected between 170 and 900 K, showing the absence of disproportionation reaction. Instead of oxidizing CO molecules, oxygen atoms stemming from the dissociation of CO attached to the reduced centers of titania, indicating the role of adsorption sites at the perimeter of Rh particles in the decomposition process. 2 ML of predeposited Mo enhanced markedly the dispersion of Rh particles as a result of strong Rh-Mo interaction, but it slightly reduced the molecular α-CO desorption possibly due to enhanced dissociation. The formation of γ-CO was suppressed considerably through elimination of adsorption centers by Mo on the TiO2 substrate. The reactivity of Rh layers deposited on Mo-covered surface towards CO was reduced after repeated annealing to 600 K due to partial encapsulation of Rh by titania, manifesting in the suppression of the more strongly bonded α-state. Mo-deposits (up to 0.5ML) on Rh particles decreased the saturation coverage of α-CO through a site-blocking mechanism without detectable influence on the binding energy of CO to Rh, indicating Mo island formation. The carbon arising from the decomposition of CO dissolved in the Mo-containing particles formed a solid solution stable even at 900 K, suggesting a possible role of molybdenum carbide regarding the enhanced catalytic activity of Rh clusters.

AB - The structural and chemical characterization of Rh, Mo and Rh-Mo nanosized clusters formed by physical vapor deposition on TiO2 single crystal was performed by Auger Electron Spectroscopy (AES), Thermal Desorption Spectroscopy (TDS) and Reflection Absorption Infrared Spectroscopy (RAIRS), applying CO as test molecule. On a slightly reduced titania surface 2D-like growth of Rh was revealed at 300 K up to 0.23 ML coverage by AES and CO-desorption experiments. For CO-saturated Rh particles TDS showed molecular CO desorption in a broad temperature range with Tp = 400, 440, 490 and 540 K (α-states), the latter state appearing only on the smallest Rh particles. The population of γ-state (Tp = 780-820 K) originating from the recombination of C and O atoms on the support began at ΘRh = 0.23ML and was maximized at around 1-2 ML Rh coverage, corresponding to 30% dissociation of CO. A possible dissociation precursor on Rh particles is identified as linearly bonded CO on step sites characterized by ν(C-O) of 2017 cm- 1. Deliberation of CO2 could not be detected between 170 and 900 K, showing the absence of disproportionation reaction. Instead of oxidizing CO molecules, oxygen atoms stemming from the dissociation of CO attached to the reduced centers of titania, indicating the role of adsorption sites at the perimeter of Rh particles in the decomposition process. 2 ML of predeposited Mo enhanced markedly the dispersion of Rh particles as a result of strong Rh-Mo interaction, but it slightly reduced the molecular α-CO desorption possibly due to enhanced dissociation. The formation of γ-CO was suppressed considerably through elimination of adsorption centers by Mo on the TiO2 substrate. The reactivity of Rh layers deposited on Mo-covered surface towards CO was reduced after repeated annealing to 600 K due to partial encapsulation of Rh by titania, manifesting in the suppression of the more strongly bonded α-state. Mo-deposits (up to 0.5ML) on Rh particles decreased the saturation coverage of α-CO through a site-blocking mechanism without detectable influence on the binding energy of CO to Rh, indicating Mo island formation. The carbon arising from the decomposition of CO dissolved in the Mo-containing particles formed a solid solution stable even at 900 K, suggesting a possible role of molybdenum carbide regarding the enhanced catalytic activity of Rh clusters.

KW - Carbon deposit

KW - Carbon monoxide

KW - Dissociation precursor

KW - Encapsulation

KW - Mo-Rh nanoparticles

KW - Perimeter sites

KW - Reduced titania support

KW - Site-blocking

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