Die Kristallstruktur von Li2Pt(OH)6 und Na2Pt(OH)6

Trömel, M.; Lupprich, E.

doi:10.1002/zaac.19754140207

Cited by 39 publications

(26 citation statements)

References 9 publications

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“…The increase in TOF of Pt in NaY and K-USY with increasing number of protons (and decreasing number of Na + /K + ) is in agreement with other studies [3,[9][10][11][12][13]20,[35][36][37][38]. Although the TOF of Pt in H-USY is higher than that in H-Y, the enhancement in the TOF with the number of protons is similar in both zeolites.…”

Section: Catalysissupporting

confidence: 90%

“…The potential type, the real and imaginary contributions to the potential, S 2 0 and the Debye-Waller factor were varied until the generated references fitted optimally the first co-ordination shell of the experimental, background subtracted XAFS spectra for Pt foil [34] and Na 2 Pt(OH) 6 [35] for the Pt-Pt and Pt-O references, respectively. More details on generating the theoretical references can be found in [32].…”

Section: Xafs Data Analysis Methodsmentioning

confidence: 99%

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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: Catalysissupporting

confidence: 90%

Section: Xafs Data Analysis Methodsmentioning

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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“…Bond lengths and angles within the octahedron are given in Table 2. The octahedron is regular within the limits of experimental error, and the mean Pt-O distance of 2.08 A is in fair agreement with the values of 2.11, 2.05 and 1.96 A found for the Li, Na and K salts respectively (Tr6mel & Lupprich, 1975;Bj6rling, 1941). the remaining distances between octahedra are >2.98 A.…”

supporting

confidence: 78%

“…This study was undertaken to establish the structural formula of platinic acid, which has been written variously as PtO2.4H20, Pt(OH)4.2H20 and, most commonly, H2Pt(OH)6 (Mellor, 1937;Hartley, 1973). While the crystal structures of its Li, Na and K salts have been determined (Tr6mel & Lupprich, 1975;Bjfrling, 1941), previous X-ray data on the parent acid appear to be limited to an incomplete description of its unindexed powder pattern (Keenan, Giesemann & Smith, 1954).…”

mentioning

confidence: 99%

The structure of platinic acid

Scott¹

1979

Acta Crystallogr Sect B

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“…Theoretical phase shifts and backscattering amplitudes for the Pt-Pt and Pt-O scattering pairs were generated utilizing the FEFF7 (24) code. These phase shifts and backscattering amplitudes were calibrated (25) with the help of XAFS spectra for Pt foil (26) and Na 2 Pt(OH) 6 (27). Details of the EXAFS analysis of the Pt/Y, Pt/LTL, Pt/SiO 2 -Al 2 O 3 , and Pt/MgO-Al 2 O 3 data are given in Refs (8), (11), and (16), respectively.…”

Section: Exafs Analysis and Separation Of Axafs From The Oscillatory mentioning

confidence: 99%

Nature of the Metal–Support Interaction in Supported Pt Catalysts: Shift in Pt Valence Orbital Energy and Charge Rearrangement

Ramaker

Graaf

Veen

et al. 2001

Journal of Catalysis

102

132

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Conversion of neopentane (hydrogenolysis and isomerizationwere performed using the FEFF7 code. The electron charge on the three "support" oxygens was changed from +0.05 to −0.01 electron to mimic changes in the support Madelung potential, which for the cluster is dominated by the nearest neighbor oxygen charge. The trends found in these theoretical AXAFS results are in excellent agreement with the experimental Pt AXAFS data and suggest that a metal cluster-support potential model is adequate for describing the changes seen in the experimental AXAFS. The experimental AXAFS results can also be understood using a molecular orbital scheme. This molecular orbital scheme further indicates that the metal-support interaction not only changes the ionization potential of the Pt valence orbitals but also induces a charge rearrangement from the Pt 6s orbitals within the particle to the oxygens of the Ptsupport interface and vice versa. This charge rearrangement is also indicated by the AXAFS through the shift, R, in AXAFS peak position. Both effects influence the electronic structure of the Pt particles. The changes in the electronic structure alter the catalytic properties of the Pt surface atoms by varying the bond strength and bond order (single or bridged) to the catalytic intermediates. The consequences of the metal-support interaction for tailor-made supported metal catalysts will be discussed.

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Die Kristallstruktur von Li₂Pt(OH)₆ und Na₂Pt(OH)₆

Cited by 39 publications

References 9 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

The structure of platinic acid

Nature of the Metal–Support Interaction in Supported Pt Catalysts: Shift in Pt Valence Orbital Energy and Charge Rearrangement

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