Correlation between CO frequency and Pt coordination number. A DRIFT study on supported Pt catalysts

Kappers, M. J.; Maas, J.H. van der

doi:10.1007/bf00769171

Cited by 191 publications

(203 citation statements)

References 20 publications

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“…The low coordinated Pt sites are more active for the hydrogenation of NB than for that of ST. Table 4, Figure 5 The present results demonstrate that smaller TiO2 crystallite size is effective for the formation of a larger fraction of low coordinated Pt sites on the surface of dispersed Pt particles. The FTIR results of adsorbed CO indicate the absence of cationic Pt sites on the surface of Pt/TiO2 catalysts reduced at 200 ºC, which is detected by a CO absorption at a higher frequency > 2125 cm -1 [19,23]. The degree of Pt dispersion is not so different among the Pt/TiO2 catalysts as compared to large differences in the crystallite size and in the surface area among the TiO2 supports (Tables 1, 2).…”

Section: Resultsmentioning

confidence: 92%

“…There existed CO absorption bands in the range of frequency of 2000 -2100 cm -1 and the absorption occurred in different frequency regions depending on the catalysts examined. The absorption band at around 2050 cm -1 may be due to a linear type of CO adsorption; the absorption band at 2070 -2100 cm -1 should be the absorption of CO adsorbed on highly coordinated Pt surfaces like Pt(111) and Pt(100) while that at 2000 -2066 cm -1 on low coordinated Pt sites like kink, edge, and corner ones [18][19][20][21][22][23]. An attempt was made to separate the absorption band measured into two (or three) independent bands to estimate the relative quantities of saturated (highly coordinated) and unsaturated (low coordinated) Pt sites on the catalysts.…”

Section: Resultsmentioning

confidence: 99%

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Influence of Crystallite Size of TiO2 Supports on the Activity of Dispersed Pt Catalysts in Liquid-Phase Selective Hydrogenation of 3-Nitrostyrene, Nitrobenzene, and Styrene

et al. 2014

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Supported Pt catalysts were prepared using several kinds of TiO2 supports different in the crystallite size in the range of 10 -500 nm and their catalytic activity was tested for the liquid-phase hydrogenation of 3-nitrostyrene, nitrobenzene, and styrene. With Pt on smaller TiO2 crystallites (nanocrystals), the selectivity to vinylaniline was improved in the hydrogenation of 3-nitrostyrene (regioselective hydrogenation) and the selectivity to aniline was promoted in the hydrogenation of a mixture of nitrobenzene and styrene (chemoselective hydrogenation). The effects of TiO2 crystallite size were discussed on the basis of the results of turnover frequency and FTIR of CO adsorbed on dispersed Pt particles.Low coordinated and/or electron-rich Pt sites should be formed on the surface of nanocrystal TiO2 supports. Nanocrystal TiO2 support is an important factor for controlling and improving the catalytic performance of dispersed Pt particles.

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Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Influence of Crystallite Size of TiO2 Supports on the Activity of Dispersed Pt Catalysts in Liquid-Phase Selective Hydrogenation of 3-Nitrostyrene, Nitrobenzene, and Styrene

et al. 2014

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“…The frequency of carbon monoxide molecules adsorbed onto group VIII metal particles has been shown to be influenced by the coordination number of the metal adsorption site involved. 27,[41][42][43][44][45][46][47][48] The linearly bonded CO frequency decreases with a decreasing number of neighboring metal atoms, i.e., with an increasing degree of coordinative unsaturation. Theoretical and experimental results [73][74][75][76][77][78] indicate that coordinatively unsaturated metal sites have a higher d valence electron band filling at the Fermi level due to the narrowing of the local density of states (LDOS) and a center-of-gravity shift to lower binding energy.…”

Section: Resultsmentioning

confidence: 99%

Deconvolution and Curve Fitting of IR Spectra for CO Adsorbed on Pt/K-LTL: Potassium Promoter Effect and Adsorption Site Distribution

1996

Self Cite

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Diffuse reflectance infrared (DRIFT) spectra have been obtained for carbon monoxide adsorbed with and without H 2 O on Pt/K-LTL zeolite. The complex spectra of CO linearly adsorbed on highly dispersed Pt have been analyzed by the combination of Fourier self-deconvolution and curve fitting. The linear-CO spectrum is composed of two broad multiplets: a high-frequency band (HFB) at 2100-1980 cm -1 and a low-frequency band (LFB) at 1990-1860 cm -1 . The relative intensities of the HFB and LFB depend on the amount of coadsorbed water in the zeolite pores. The LFB is associated with an ion-dipole interaction between the oxygen atoms of CO species with potassium cations from the zeolite support. The HFB is associated with linear-CO unperturbed by the alkali promoter effect. It is proposed that water preferentially adsorbs on the K + ions, shielding the ion-dipole interaction. The individual components of the complex HFB and LFB are proposed to be due to CO molecules adsorbed on platinum atoms with different coordination numbers. The average coordination number of the Pt atoms in K-LTL, determined in the applied deconvolution and curvefitting program, corresponds well with that obtained by EXAFS, indicating a metal particle size distribution with particles containing between 1 and 13 platinum atoms. By applying the newly developed method, several literature IR CO spectra of Pt/K-LTL with different relative intensities in the HFB region have been analyzed successfully by adjusting the particle size distribution only. In view of the new results showing the prominent effects of particle size distribution and potassium promotion on the IR spectra of adsorbed CO, previously reported conclusions concerning metal-support interactions in PT/K-LTL should be reconsidered when based on infrared spectroscopic data.

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“…A lower coordination number results in an increased electron density and hence a shift to lower frequency of the linear-CO band. 40 Hence, the observed shift to higher frequency of the maximum of the linearly adsorbed CO band can be explained by an increase in the particle size. The frequency of the peak associated with linearly adsorbed CO, Le., 2071 -2081 cm-I, is close to the frequency observed for CO on a Pt( 11 1) singlecrystal surface, i.e., 2084 cm-', 41 in agreement with the observed metallic state of the platinum by EXAFS.…”

Section: Pt-pt Distance (277 A) a Contraction Of The Metal-metalmentioning

confidence: 96%

Hydrogen as a Modifier of the Structure and Electronic Properties of Platinum in Acidic Zeolite LTL: A Combined Infrared and X-ray Absorption Spectroscopy Study

Vaarkamp¹,

Mojet²,

Kappers³

et al. 1995

J. Phys. Chem.

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The structure and electronic properties of platinum in WH-LTL after reduction at 300 "C and heating in helium to 500 or 690 "C were determined using X-ray absorption and infrared spectroscopy. After reduction at 300 "C, the platinum particles were metallic, consisted of 4 or 5 atoms, and were located at 2.64 A from the oxygen atoms in the zeolite framework. The particles remained metallic but increased in size to e 1 3 atoms during hydrogen desorption by heating in a helium flow up to 690 "C. Simultaneously, the distance between metal particle and oxygen atoms of the zeolite framework was shortened to 2.05 A. After reduction at 300 "C and in the presence of chemisorbed hydrogen, the platinum atoms in the PT/H-LTL catalyst had more holes in the d-band than bulk platinum. Hydrogen desorption decreased the number of holes of the platinum atoms in the WH-LTL catalyst to levels lower than bulk metal values. The linear CO band shifted from 2071 to 2084 cm-' upon hydrogen desorption, due to the increased particle size andor the change in the structure of the metal-support interface. The apparent contradiction between the shift to higher wavenumbers of the linear CO band and the decreased number of holes in the d-band was attributed to the interaction of CO with filled d-orbitals and the effect of chemisorbed hydrogen on the distribution of the local density of states.

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Correlation between CO frequency and Pt coordination number. A DRIFT study on supported Pt catalysts

Cited by 191 publications

References 20 publications

Influence of Crystallite Size of TiO2 Supports on the Activity of Dispersed Pt Catalysts in Liquid-Phase Selective Hydrogenation of 3-Nitrostyrene, Nitrobenzene, and Styrene

Influence of Crystallite Size of TiO2 Supports on the Activity of Dispersed Pt Catalysts in Liquid-Phase Selective Hydrogenation of 3-Nitrostyrene, Nitrobenzene, and Styrene

Deconvolution and Curve Fitting of IR Spectra for CO Adsorbed on Pt/K-LTL: Potassium Promoter Effect and Adsorption Site Distribution

Hydrogen as a Modifier of the Structure and Electronic Properties of Platinum in Acidic Zeolite LTL: A Combined Infrared and X-ray Absorption Spectroscopy Study

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