Electronic state of platinum supported on the monochlorotrifluoromethane-treated alkaline L zeolite

Sugimoto, Michio; Katsuno, Hisashi; Hayasaka, Toshiaki; Ishikawa, Norio; Hirasawa, Ken-ichi

doi:10.1016/0926-860x(93)80227-h

Cited by 27 publications

(15 citation statements)

References 11 publications

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“…de Mallman and Barthomeuf proposed that the shift to lower frequency in the infrared spectra of adsorbed CO was due to a higher electron density of Pt on alkaline Y zeolite [11,12]. Finally, XPS data suggest that zeolite supported Pt and Pd clusters are electron deficient [13,14] on acidic supports and electron rich on alkaline supports [13,15].…”

Section: Introductionmentioning

confidence: 96%

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The metal–support interaction in Pt/Y zeolite: evidence for a shift in energy of metal d-valence orbitals by Pt–H shape resonance and atomic XAFS spectroscopy

Koningsberger

Graaf

Mojet

et al. 2000

Applied Catalysis A: General

108

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The turnover frequency (TOF) for conversion of neo-pentane was determined for Pt in Y zeolite with different numbers of protons and La +3 ions, different Si/Al ratios and with non-framework Al being present. Comparing Pt/NaY to Pt/H-NaY and Pt/K-USY with Pt/H-USY, respectively, shows an increase in the ln (TOF) which is proportional to the number of protons. Compared to NaY, the TOF of Pt in non-acidic NaLaY zeolite is about 25 times higher, which indicates also a strong influence on the charge of the cations on the TOF of Pt. The 20 times increase in the Pt TOF for K-USY compared to NaY is attributed to the effect of a higher Si/Al ratio and non-framework Al in the K-USY.EXAFS data collected on Pt/NaY and Pt/H-USY showed platinum particles consisting of 14-20 atoms on an average. These results were confirmed by HRTEM, which also showed that the Pt particles were dispersed inside the zeolite. The EXAFS data indicate that the metal particles are in contact with the oxygen ions of the support. The peak in the Fourier transform of the atomic XAFS (AXAFS) spectrum of the Pt/H-USY is larger in intensity than the corresponding peak of the Pt/Na-Y data. A detailed analysis of the L 2 and the L 3 X-ray absorption near edge structure revealed a shape resonance due to the Pt-H anti-bonding state (AS) induced by chemisorption of hydrogen on the surface of the platinum metal particles. The difference in energy (E res ) between the AS and the Fermi-level (E F ) is 4.7 eV larger for Pt/H-USY than for Pt/NaY. Both the AXAFS spectra and the shape resonances of the Pt-NaY and the Pt/H-USY catalysts provide direct experimental evidence of how the support properties determine the electronic structure of the platinum metal particles.Previous AXAFS and shape resonance work lead to a model in which the position in energy of the Pt valence orbitals is directly influenced by changes in the potential (i.e. electron charge) of the oxygen ions of the support and how the proton density affects this oxygen charge. This work shows that the potential of the oxygen ions is also a function of the Si/Al ratio of the support and the polarisation power of the charge compensating cations (H + , Na + , La 3+ and extra-framework Al); the metal particles experience an interaction which is determined by several properties of the support. The data further reveal how the change in the Pt electronic structure directly influences the catalytic properties of the catalyst.While the TOF is dependent on the metal-support interaction, the hydrogenolysis selectivity is determined by the Pt particle size, and increases linearly with increasing dispersion, or decreasing particle size.

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Section: Introductionmentioning

confidence: 96%

“…2. Charge transfer between the metal atoms and the nearest neighbour zeolite oxygen atoms [10][11][12]15]. It has been suggested that the Sanderson electronegativity of the nearby support oxygen atoms increases with increasing zeolite alkalinity [10,11].…”

Section: Introductionmentioning

confidence: 99%

The metal–support interaction in Pt/Y zeolite: evidence for a shift in energy of metal d-valence orbitals by Pt–H shape resonance and atomic XAFS spectroscopy

Koningsberger

Graaf

Mojet

et al. 2000

Applied Catalysis A: General

108

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“…Charge transfer between support oxygen atoms and the nearby metal particles actually increases the electron density of the metal particles (2,7,8). However, since the support material is an insulator, electron transfer to or from the support is unlikely.…”

Section: A New Model Describing the Metal-support Interaction In Noblmentioning

confidence: 99%

“…However, such proton adducts cannot account for an increase in electron density for metal particles on alkaline supports. Alternatively, it was proposed that with increasing support alkalinity, the electron density of the support oxygen atoms increases (2,7,8). Electron transfer between the support oxygen atoms and the nearby metal particles is thought to increase the electron density on the metal particles.…”

Section: Introductionmentioning

confidence: 99%

A New Model Describing the Metal–Support Interaction in Noble Metal Catalysts

Mojet

Miller²,

Ramaker

et al. 1999

Journal of Catalysis

217

191

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The catalytic activity and spectroscopic properties of supported noble metal catalysts are strongly influenced by the acidity/ alkalinity of the support but are relatively independent of the metal (Pd or Pt) or the type of support (zeolite LTL or SiO 2 ). As the alkalinity of the support increases, the TOF of the metal particles for neopentane hydrogenolysis decreases. At the same time, there is a decrease in the XPS binding energy and a shift from linear to bridge bonded CO in the IR spectra. Analysis of the shape resonance in XANES spectra indicates that in the presence of chemisorbed hydrogen the difference in energy between the Pt-H antibonding orbital and the Fermi level decreases as the alkalinity of the support increases. Based on the results from the IR, XPS, and shape resonance data a new model is proposed in which the interaction between the metal and support leads to a shift in the energy of the metal valence orbitals. The EXAFS structural analysis indicates that the small metal particles are in contact only with the oxide ions of the support. Finally, a new spectroscopic characterisation, Atomic XAFS, is presented which provides new insights into the origin of the electronic changes in the metal. As the alkalinity of the support increases, there is decrease in the metal ionisation potential. The primary interaction is a Coulomb attraction between metal particle and support oxygen ions, which affects the metal interatomic potential. This model for the metal-support interaction explicitly excludes the need for electron transfer, and it can account for all observed changes in the catalytic, electronic, and structural properties of the supported metal particles induced by support acidity ranging from acidic to neutral to alkaline.

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“…Several explanations for the metal-support interaction have been proposed in the literature: (i) formation of a metal-proton adduct [5,8], (ii) charge transfer between the metal atoms and the nearest neighbor zeolite oxygen atoms [9][10][11][12], and (iii) polarization of the metal particles by nearby cations of the support [13,14]. These explanations contains deficiencies: (i) proton adducts cannot account for an increase in electron density on the metal clusters in alkaline zeolites, (ii) significant direct transfer of electrons is very unlikely, as argued by Ponec et al [15], and (iii) experiments underlying the theoretical calculations suggesting polarization by cations are lacking.…”

Section: Introductionmentioning

confidence: 99%

In situ X-ray absorption spectroscopy as a unique tool for obtaining information on hydrogen binding sites and electronic structure of supported Pt catalysts: towards an understanding of the compensation relation in alkane hydrogenolysis

Koningsberger

Oudenhuijzen

Graaf

et al. 2003

Journal of Catalysis

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L 2 and L 3 X-ray absorption near edge spectra (XANES) on supported Pt particles, with and without chemisorbed hydrogen, are shown to reflect the type of hydrogen-binding site on the Pt surface. FEFF8 ab initio multiple scattering calculations are used to determine XANES spectral fingerprints for the atop vs threefold H binding sites on Pt. Comparison of the experimental XANES data with the theoretical fingerprints, and further theoretical results, show that the acid/base properties of the support have a profound influence on the hydrogen coverage, and therefore on the mode of hydrogen adsorption on the Pt surface. As the electron richness of the support oxygen atoms increases (i.e., with increasing alkalinity of the support), the H coverage increases and the hydrogen-binding site of the strongly adsorbed hydrogen changes from atop to threefold. This site change is primarily responsible for the observed changes in previously reported kinetic data, which show an increase in negative order (roughly from −1.5 to −2.5) in hydrogen partial pressure for neopentane hydrogenolysis with increasing support alkalinity. This change in negative order directly reflects the greater number of vacant Pt sites that must be available to allow adsorption of the neopentane. A compensation relation is found in the kinetic data of Pt on different supports resulting directly from this change in hydrogen coverage. This implies that the experimentally determined kinetic parameters are apparent values. These apparent values are correlated to the intrinsic kinetic parameters via the thermodynamic properties of the sorption of the reactants, described by the Temkin equation. The TOF of neopentane hydrogenolysis over several catalysts, measured in previous work, decreases with the increasing alkalinity of the support. This can now be directly explained as the result of the change in hydrogen coverage using a Frumkin isotherm, implying that the neopentane adsorption becomes weaker with increased hydrogen coverage. These conclusions, that hydrogen drives the catalysis, are further supported by density functional calculations on small Pt 4 clusters, which show that the acid/base properties of the support have a much larger direct influence on Pt-H bonding than on Pt-CH n bonding.

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Electronic state of platinum supported on the monochlorotrifluoromethane-treated alkaline L zeolite

Cited by 27 publications

References 11 publications

The metal–support interaction in Pt/Y zeolite: evidence for a shift in energy of metal d-valence orbitals by Pt–H shape resonance and atomic XAFS spectroscopy

The metal–support interaction in Pt/Y zeolite: evidence for a shift in energy of metal d-valence orbitals by Pt–H shape resonance and atomic XAFS spectroscopy

A New Model Describing the Metal–Support Interaction in Noble Metal Catalysts

In situ X-ray absorption spectroscopy as a unique tool for obtaining information on hydrogen binding sites and electronic structure of supported Pt catalysts: towards an understanding of the compensation relation in alkane hydrogenolysis

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