Metal Particle Size Determination of Supported Metal Catalysts

Whyte, T.E.

doi:10.1080/01614947408071858

Cited by 73 publications

(8 citation statements)

References 58 publications

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“…Although originally intended for 0.7 wt%, the actual metal loadings converted from Pt uptake varied moderately and have been listed in Table 3. Here it should be noted that XRD and chemisorption reveal volume (d v,XRD ) and surface (d s,chemi ) averaged particle sizes respectively [32]. These values were compared with the respective volume and surface averaged particle size obtained from STEM images.…”

Section: Characterization Of Reduced Pt/al-simentioning

confidence: 99%

The controlled synthesis of metal-acid bifunctional catalysts: Selective Pt deposition and nanoparticle synthesis on amorphous aluminosilicates

Samad

Blanchard

Sayag

et al. 2016

Journal of Catalysis

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The rational synthesis of metal-acid bifunctional catalysts based on aluminosilicates will involve control over which domain -alumina or silica -the metal can be deposited on, as well as the control of particle size. These factors determine the ratio and proximity of the metal and acid sites. The control of adsorption selectivity and particle size has been studied by measuring the uptake of anionic and cationic Pt precursors as a function of pH over various types of silicaalumina composites and pure oxide supports, followed by characterization of the nanoparticles resulting from reduction of the precursors.Results indicate that electrostatic adsorption can be exploited to achieve selective deposition. Ion exchange of cationic precursors also appears to occur over the acid sites. Cationic tetraammine Pt precursors, either electrostatically adsorbed onto silica domains at high pH, or ion exchanged at the acidic alumina-silica adlineation (interface between two oxides) at neutral pH, lead to small (1.7-3.0 nm) nanoparticles. The size of Pt nanoparticles resulting from anionic Pt hexachloride electrostatically deposited onto alumina domains at low pH depends on the size of the alumina domain; a critical domain size is needed to anchor the Pt precursors against sintering.In the companion paper, the factors controlling metal-acid site intimacy and ratio are demonstrated for the isomerization of n-heptane.

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Section: Characterization Of Reduced Pt/al-simentioning

confidence: 99%

The controlled synthesis of metal-acid bifunctional catalysts: Selective Pt deposition and nanoparticle synthesis on amorphous aluminosilicates

Samad

Blanchard

Sayag

et al. 2016

Journal of Catalysis

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“…A convenient measure of particle size is the dispersion (Boudart, 1969), defined as the ratio of two numbers: the number of surface metal atoms and the total number of metal atoms. Dispersion D may be obtained by selective chemisorption of a gas to titrate surface atoms of a given kind (Benson and Boudart, 1965;Whyte, 1973). Naturally, it is important, before classifying a reaction to be either structure insensitive or structure sensitive, that no artifacts such as metal support interactions, catalyst deactivation and poisoning, or transport effects play any role while determining the catalytic activity.…”

Section: Page 904mentioning

confidence: 99%

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

1978

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The areal rate of liquid phase hydrogenation of cyclohexene on supported platinum catalysts does not depend on the nature of the support. Nor does it depend on particle size of the metal. The rate constant is independent of the nature of the solvent when the concentration of hydrogen in it is expressed as its measured or calculated solubility. All observations are compatible with the idea that the measured rate is that of chemisorption of dihydrogen on a metal surface covered with reactive hydrocarbon intermediates. SCOPEThe effect of the dimensions of metallic particles on the catalytic activity of supported metals is of theoretical and practical importance. The present work was undertaken to examine the effect of platinum particle size on the liquid phase hydrogenation of cyclohexene in a rocking slurry reactor. The reaction was studied in a static system at constant hydrogen pressure, normally atmospheric pressure, between 275O and 316OK. As diffusion coefficients in the liquid phase are often two or more orders of magnitude lower than in the vapor phase, diffusional influence can play a substantial role in slurry reactors. It is thus imperative that reactions studied in slurry reactors be examined for diffusional effects and proof be given that observed rates have not been disguised by either intraparticle or interphase mass transport. We set out to obtain true kinetic data devoid of either the influence of transport phenomena or catalyst deactivation during an experimental run.The present study also focused on two important aspects of liquid phase reactions, When heterogeneous catalytic reactions are carried out in the gas phase, ideal gas behavior is ordinarily assumed. However, for kinetics in the liquid phase, as in a slurry or trickle bed reactor, it is necessary first of all to ascertain whether concentrations or activities of dissolved reactants should be used in rate expressions. Second, it is also important to check whether different solvents affect the reaction rate or the rate constant. The literature of catalytic reaction engineering offers few experimental or theoretical guidelines bearing on these two important questions. CONCLUSIONS AND SIGNIFICANCEKinetic data have been obtained for the liquid phase hydrogenation of cyclohexene on supported platinum catalysts in a rocking slurry reactor. First of all, values of the turnover frequency N , defined as molecules reacted per site per second, were obtained on catalysts containing different amounts of platinum of the same dispersion, defined as the ratio of surface metal atoms to total metal atoms. Values of N were found to be identical. As this re- Page 904September, 1978 sult was obtained at two different temperatures, it offers sufficient proof that rates were not masked by artifacts such as the influence of interphase and intraparticle heat and mass transfer, or deactivation and poor contacting of the catalyst by reactants. The main result of this work is that values of N were identical on nine different supported platinum catalysts where the me...

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“…Metal dispersions are then calculated by assuming a H* to surface‐metal (H:M s ) stoichiometry at saturation ( θ sat , often assumed to be unity), and particle sizes can be estimated from dispersion for a given particle shape (e.g., hemispherical, spherical). X‐ray diffraction (XRD) and transmission electron microscopy (TEM) can confirm these particle size estimates; however, small metal particles (<1 nm in diameter) are difficult to observe in standard TEM instruments and their sizes are inaccurately estimated using XRD . For these highly dispersed noble metal catalysts, the most common estimate of their size is given by H 2 chemisorption, which requires an accurate estimate of saturation H* coverages during chemisorption experiments.…”

Section: Introductionmentioning

confidence: 99%

Supra‐monolayer coverages on small metal clusters and their effects on H₂ chemisorption particle size estimates

Almithn

Hibbitts

2018

AIChE Journal

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H 2 chemisorption measurements are used to estimate the size of supported metal particles, often using a hydrogen-tosurface-metal stoichiometry of unity. This technique is most useful for small particles whose sizes are difficult to estimate through electron microscopy or X-ray diffraction. Undercoordinated metal atoms at the edges and corners of particles, however, make up large fractions of small metal clusters, and can accommodate multiple hydrogen atoms leading to coverages which exceed 1 ML (supra-monolayer). Density functional theory was used to calculate hydrogen adsorption energies on Pt and Ir particles (38-586 atoms, 0.8-2.4 nm) at high coverages (3.63 ML). Calculated differential binding energies confirm that Pt and Ir (111) single-crystal surfaces saturate at 1 ML; however, Pt and Ir clusters saturate at supra-monolayer coverages as large as 2.9 ML. Correlations between particle size and saturation coverage are provided that improve particle size estimates from H 2 chemisorption for Pt-group metals.

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Metal Particle Size Determination of Supported Metal Catalysts

Cited by 73 publications

References 58 publications

The controlled synthesis of metal-acid bifunctional catalysts: Selective Pt deposition and nanoparticle synthesis on amorphous aluminosilicates

The controlled synthesis of metal-acid bifunctional catalysts: Selective Pt deposition and nanoparticle synthesis on amorphous aluminosilicates

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

Supra‐monolayer coverages on small metal clusters and their effects on H₂ chemisorption particle size estimates

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Metal Particle Size Determination of Supported Metal Catalysts

Cited by 73 publications

References 58 publications

The controlled synthesis of metal-acid bifunctional catalysts: Selective Pt deposition and nanoparticle synthesis on amorphous aluminosilicates

The controlled synthesis of metal-acid bifunctional catalysts: Selective Pt deposition and nanoparticle synthesis on amorphous aluminosilicates

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

Supra‐monolayer coverages on small metal clusters and their effects on H2 chemisorption particle size estimates

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Supra‐monolayer coverages on small metal clusters and their effects on H₂ chemisorption particle size estimates