Stepped single-crystal surfaces as models for small catalyst particles

Greenler, Robert G.; Burch, Kathryn D.; Kretzschmar, K.; Klauser, Ruth; Bradshaw, Alexander M.; Hayden, Brian E.

doi:10.1016/0039-6028(85)90163-3

Cited by 124 publications

(106 citation statements)

References 11 publications

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“…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%

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: 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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“…To achieve this comparison, it is most convenient to calculate a quantity called the dipole shift value, 8(0) [31,32], which has been used in previous studies on Pt( 11)/CO [27,31,32]. The dipole shift value is defined as the difference between the square of the measured adlayer vibrational frequency at a specified coverage and the square of the singleton value for that 14 coverage (8(0) = v 2 (0) -v 0 2 (0)). This quantity is similar to Avd, but is used because it bears a simple, direct relationship to the interaction force constants [31,32].…”

Section: Coverage-dependent Experimentsmentioning

confidence: 99%

“…Several recent papers in this area have reported on site-dependent phenomena at Pt(335) (Pt-(S)-[4(l 11) x (100)]) [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. This surface was originally used to support infrared spectroscopic studies of carbon monoxide (CO) adsorption at defect sites on small platinum catalyst particles [13,14], and it has since become a model substrate for vibrational studies of site-dependent adsorption processes.…”

Section: Introductionmentioning

confidence: 99%

“…This surface was originally used to support infrared spectroscopic studies of carbon monoxide (CO) adsorption at defect sites on small platinum catalyst particles [13,14], and it has since become a model substrate for vibrational studies of site-dependent adsorption processes. The earliest experiments defined conditions for observing independent vibrational spectral features for molecules on Pt(335) step edges (edge-CO) and for molecules on Pt(335) terrace planes (terrace-CO) [12,13].…”

Section: Introductionmentioning

confidence: 99%

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Site-dependent vibrational coupling of CO adsorbates on well-defined step and terrace sites of monocrystalline platinum: Mixed-isotope studies at Pt(335) and Pt(111) in the aqueous electrochemical environment

Kim

Tornquist

Korzeniewski

1994

The Journal of Chemical Physics

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Infrared spectroscopy is applied to probe qualitative structural features of the adlayers formed by CO at step sites and on terrace planes of Pt(335){Pt(S)-[4(111)×(100)]} in the aqueous electrochemical environment. The C–O stretching vibrational features are reported for adlayers formed from 12CO/13CO isotopic mixtures over a wide range of CO surface coverages. At saturation, the predominant spectral features are associated with the vibrational modes of terrace-CO in terminal (atop) coordination environments. The position of the 12CO and 13CO spectral features and their relative intensity are examined for several 12CO/13CO fractions, and they are shown to display the characteristics of a strongly coupled system. In comparison with corresponding mixed isotope spectra for CO at Pt(111) electrodes, intermolecular coupling for terrace-CO on the (111) surface planes of Pt(335) is observed to be significantly stronger, reflecting the higher CO surface coverages on the edge sites and the terrace sites of the Pt(335) surface plane. At low coverages, spectral features associated with edge-CO are discerned, and the intermolecular coupling for atop CO is weaker than for corresponding coverages of CO at Pt(111). The weak coupling at low coverages is attributed to the exclusive CO occupation at the step edges, which confines the intermolecular coupling to one dimension, in the direction along the step edges. For all coverages, values are determined for the dynamic dipole–dipole coupling parameter (Δνd) and the chemical (static–dipole) shift parameter (Δνs). Values for Δνs are generally small at all coverages. Values for Δνd are small (<8 cm−1) at low coverages, where CO forms one-dimensional structures along the step edges, and they increase to large values (∼42 cm−1) at coverages that coincide with the growth of two-dimensional structures on the terrace planes. The majority of measurements were made for the Pt(335) electrode at potentials in the classical double-layer region, although dipole coupling parameters are also reported for Pt(335)/CO at potentials in the hydrogen adsorption region, where Δνd approaches zero at low coverages.

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“…[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%

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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Stepped single-crystal surfaces as models for small catalyst particles

Cited by 124 publications

References 11 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

Site-dependent vibrational coupling of CO adsorbates on well-defined step and terrace sites of monocrystalline platinum: Mixed-isotope studies at Pt(335) and Pt(111) in the aqueous electrochemical environment

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

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