Site-specific, coupled-harmonic-oscillator model of carbon monoxide adsorbed on extended, single-crystal surfaces and on small crystals of platinum

Brandt, Robert K.; Sorbello, R. S.; Greenler, Robert G.

doi:10.1016/0039-6028(92)90922-s

Cited by 64 publications

(59 citation statements)

References 24 publications

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“…[46][47][48] It was shown that the sharp linear-CO spectra for silica supported platinum particles can be explained in terms of the correlation between ν CO and the coordination number CN of the surface adsorption sites, the same correlation used here to interpret the CO spectra for Pt/K-LTL. The difference between CO spectra from silica and K-LTL supported platinum is mainly due to the large difference in average particle size.…”

Section: Discussionmentioning

confidence: 98%

“…Only then it is possible to compare CO (singleton) frequencies from platinum coordination sites of metal particles supported on different types of catalysts with the corresponding frequencies from electronically neutral, single crystals. [46][47][48]70 …”

Section: Resultsmentioning

confidence: 99%

“…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%

“…[19][20][21][22][23][24][25][26][27][28][29] The stretching frequency of CO is very sensitive to the electronic structure of the metal surface onto which it is chemisorbed. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] The CO spectra obtained for the nonacidic Pt/LTL zeolites differ in two ways from those obtained for platinum supported on SiO 2 , Al 2 O 3 , and H + -exchanged zeolites. 26,27 Instead of one linear-CO band in the region 2100-2040 cm -1 , for Pt/LTL there are two absorption bands: one centered around 2060 cm -1 and one at 1960 cm -1 .…”

Section: Introductionmentioning

confidence: 99%

“…Another hypothesis proposes that the frequency of CO species absorbing in the 2100-2000 -1 region depends on the degree of coordinative metal atom saturation. 27,[41][42][43][44][45][46][47][48] The series of overlapped peaks in the spectrum of Pt/K-LTL may therefore represent surface platinum atoms which vary in electron density due to their different coordination numbers. 27 To understand the origin of the high-frequency CO band components and the effect of ion-dipole interactions induced by promoter ions, we have examined the infrared spectra of a Pt/K-LTL zeolite in the presence and absence of coadsorbed water in more detail.…”

Section: Introductionmentioning

confidence: 99%

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

1996

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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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Section: Discussionmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

1996

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Density functional calculations on CO attached to PtnRu(10?n) (n = 6-10) clusters

Binning

Liao

Cabrera

et al. 2000

Int. J. Quant. Chem.

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B3LYP and SCF-Xα calculations have been performed on Pt n Ru (10−n) CO (n = 6-10) clusters. The work aims to simulate the adsorption of CO on the (111) surface of platinum metal and to examine the electronic effects that arise when some Pt atoms are replaced with Ru. Adsorption energies and Pt-C and C-O stretching frequencies have been calculated for each cluster. Ru does affect the electronic structure of the clusters, the calculated adsorption energies, and frequencies, the Pt-C frequency more than the C-O. The donation-backbonding mechanism that accompanies the shift in CO stretching frequency that occurs when CO adsorbs on platinum does not explain the differences in frequency shift observed in CO on various Pt/Ru surfaces.

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Interpretation of IR Spectra of Ultrathin Films

2003

Handbook of Infrared Spectroscopy of Ultrathin Films

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Generally speaking, IR spectral measurements of ultrathin films are undertaken to determine (i) the chemical identity of adsorbed species (including dissociation fragments); (ii) the geometric or structural arrangement (orientation) of these species and their positions with respect to the surface atoms of the substrate; (iii) their vibrational, rotational, and translational motion on the surface; (iv) the charge distribution and energy level structure of the valence electrons in both adsorbate and substrate; and (v) the effects of external perturbations, such as the electric and magnetic fields, photons, electrons, heating, and surface pressure on factors (i)-(iv) [1]. However, such information cannot be extracted directly from the IR spectra of ultrathin films due to the strong dependence of the shape and relative intensity of the bands on the geometry of the experiment, the optical properties of the substrate, the surroundings, the gradient of the optical properties at the film-substrate interface and in the film itself, as well as on the film thickness, and the particle size in the case of powder or islandlike supports. These effects and their physical background are discussed in Sections 3.1-3.5 and 3.9. In addition, there can be an intensity transfer between modes of coadsorbed species and a change in the band position with surface coverage. This effect is used for determining the mode of the surface filling and the degree of intermixing of different species at the surface (Section 3.6). If the film under study is located at the electrode-solution interface, the resulting spectrum is made up of contributions of all species in the path of radiation that are affected by the electrode potential, which further complicates the interpretation. Apart from technical means (Chapter 4), there exist analytical and mathematical approaches to resolve contributions of different species in such a complex spectrum (Sections 3.7 and 3.8). Another feature of the IR spectra of ultrathin films that is perhaps surprising and unexpected is their sensitivity to the volume fraction, shape, and orientation of inhomogeneities (e.g., pores or inclusions) in the film. Moreover, if the characteristic size of the 140

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Site-specific, coupled-harmonic-oscillator model of carbon monoxide adsorbed on extended, single-crystal surfaces and on small crystals of platinum

Cited by 64 publications

References 24 publications

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

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

Density functional calculations on CO attached to PtnRu(10?n) (n = 6-10) clusters

Interpretation of IR Spectra of Ultrathin Films

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