Splitting of platinum crystallites supported on thin, nonporous alumina films

Ruckenstein, Eli; Malhotra, Manohar L.

doi:10.1016/0021-9517(76)90345-6

Cited by 93 publications

(18 citation statements)

References 5 publications

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“…Stulga et al (1980) observed no significant change in platinum particle size for initially heat-treated samples which were subsequently "redispersed" in air at 7'73 K for 18 hours. These results are in contradiction to the observations made by Ruckenstein and Malhotra (1976) who found a decrease in Pt particle size, from 10.7 to 7.1 nm under similar heat treatment conditions. Straguzzi et al (1980) found that hydrogen-sintered, but not air-sintered, Pt/A1203 catalysts could be easily redispersed by air treatment at 773 K. However, the air-sintered catalysts were redispersed by 0 2 treatment at 773 K. Wang and Schmidt (1980) studied the effects of air and hydrogen treatments on 2-10 nm diameter particles of Ir on amorphous Si02.…”

Section: Introductioncontrasting

confidence: 86%

Modeling of sintering and redispersion of supported metal catalysts

Handa

Matthews

1983

AIChE Journal

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A model, which utilizes a Monte Carlo simulation, of the sintering and the redispersion of supported metal catalysts is presented and compared with experimental data from a PtIA1203 system. The model is based on an atomic migration mechanism, but includes instantaneous diffusion and coalescence of crystallites of size <1 nm in reducing and inert atmospheres. It was found that behavior in reducing, oxidizing and inert atmospheres could be predicted. P. K. HANDA and J. C. MATTHEWS Department of Chemical EngineeringKansas State University Manhattan, KS 66506 SCOPESupported metal catalysts are used extensively in the process industry. An early application was the reforming of naptha to high-octane gasoline using Pt on an alumina support. Most hydrogenations are done with either Ni or Pd on a suitable support. Presently, Pt along with other metals is used in the catalytic mufflers of automotive exhausts. The support makes it possible for a high percentage of the metal atoms to be exposed, thus making efficient utilization of the metal.One of the problems of supported metal catalysts is sintering, that is a decrease in metal surface area due to the growth or agglomeration of crystallites, which occurs at elevated temperatures. Several processes, among them treatment with oxygen and chlorine, have been found to achieve redispersion of the metal on the support. Obviously in situ redispersion is of considerable industrial importance as it prolongs the life of the catalyst.Fundamental studies of the processes occuring during sintering and redispersion are valuable in designing new catalysts and in reducing sintering in existing processes. Two major concepts have been employed to model the sintering and redispersion of supported metal catalysts, namely, sintering by particle migration (Ruckenstein and Pulvermacher, 1973a,b) and sintering by atomic migration (Flynn and Wanke, 1974a CONCLUSION AND SIGNIFICANCEPt crystallites on Alz03 were subjected to alternate treatments in H2 and 0 2 for various times and temperatures. It was found that sintering which occurred in Hz could be redispersed by treatment in oxygen. However, no redispersion of crystallites sintered in oxygen was obtained.A model of the phenomena was developed which viewed the behavior of hydrogen sintered catalyst when subjected to 0 2 as resulting from a very rapid loss of Pt from the crystallites to the support surface followed by slow transport on the surface and a low probability of incorporation into a crystallite upon collision. The behavior in Hz and in He was described by very rapid transport on the support surface, no resistance to capture but very slow loss of Pt from the crystallites. Using this model it was possible to predict the changes in dispersion that occur during sequences involving alternate treatments in H2 and 02.The state of the metal in an 0 2 atmosphere was described differently than in an HZ or He atmosphere. For 100% dispersion in Hz, the metal was assumed to be present as 1 nm crystallites while in 0 2 the metal was assumed to be sp...

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Section: Introductioncontrasting

confidence: 86%

Modeling of sintering and redispersion of supported metal catalysts

Handa

Matthews

1983

AIChE Journal

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“…79,80 Interestingly, it was also found that repeated oxidation cycles actually resulted in Pt sintering. 22 TEM studies have shown that the re-dispersion of Pt particles was observed from 10.7 nm to 4.1 nm after heating a Pt/γ-Al2O3 catalyst in air at 600 °C for 18 h, followed by heating at 500 °C, also in air, for a further 18 h. 81 Prior to analysis with TEM, the samples were immersed in mercuric chloride and then rinsed with water, before being stored under high vacuum for several hours to avoid any contamination of the microscope. There was no apparent reduction treatment, although the storage under high vacuum for several hours would have creating a significant reducing environment.…”

Section: Platinummentioning

confidence: 99%

“…Some re-dispersion was achieved at lower temperatures (400 11 °C) following the 600 °C treatment, but to a lesser extent that that observed after heating at 500 °C. 81 A different study reported an optimum temperature for re-dispersion of Pt (in the case of a number of pre-reduced Pt/Al2O3 catalysts). 82 In this case, oxidation at temperatures up to 600 °C, followed by a reduction with H2 at 500 °C resulted in dispersion of the Pt (30%) which was higher than that obtained with the fresh catalyst (10%).…”

Section: Platinummentioning

confidence: 99%

Metal Redispersion Strategies for Recycling of Supported Metal Catalysts: A Perspective

Morgan¹,

Goguet²,

Hardacre³

2015

ACS Catal.

177

152

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Catalyst deactivation is ultimately inevitable, and one of the processes known to cause deactivation is sintering of metal particles. Consequently, numerous methods to reverse the sintering process by re-dispersing metal nanoparticles have been developed. These methods are discussed in this perspective, and the reported mechanisms of re-dispersion are summarized. Additionally, the longer term practical use of such treatments, and the benefits this can bring, is briefly disclosed.

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“…Particle fragmentation and recrystallization has been observed for a number of high-temperature oxidation systems [25]. This effects was used by Friedorow and Wanke [26], Ruckenstein and Malhotra [27] and Flynn and Wanke [28] to redisperse Al 2 O 3 supported Pt particles which had sintered after hightemperature treatment in hydrogen. These results are also in agreement with recent findings of Yang et al who found that oxygen treatment at about 670 K leads to a disrupture of supported Ag particles to smaller subunits [29].…”

Section: K Tmentioning

confidence: 99%

High temperature partial oxidation reactions over silver catalysts

Nagy

Mestl

1999

Applied Catalysis A: General

176

115

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In honor of Prof. Dr. Wolfgang Sachtler´s 75 th birthday. AbstractThe exceptional catalytic activity of silver for a number of partial oxidation reactions has been known for nearly a century. Despite the wid espread use of silver in heterogeneous catalysis, there still remain unresolved questions about the mechanistic details of reaction. The ethylene epoxidation and formaldehyde synthesis reactions are the two industrially-relevant reactions which have received, by far, the most attention. The importance of these reactions cannot be underestimated. Both ethylene epoxide and formaldehyde serve as primary chemicals for a wide variety of materials which find use in an enormous number of products. There is, therefore, a great scientific and economi c motivation for understanding these reactions and for unraveling the secret to the exceptional catalytic a ctivity of silver. This contribution in honor of Prof. W. Sachtler´s 75 th birthday summarizes recent results obtained in our laboratory on the formaldehyde synthesis reaction and the oxidative coupling of methane as a laboratory test reaction. The article shows that the formation of bulk-dissolved oxygen species is critical to activation of the silver for reaction. Both the chemical composition and the bulk morphology of the catalyst are strong functions of the gas-phase composition and reaction temperature. Similar apparant activation energies determined for oxygen diffusion and oxidative coupling of methane suggest that the rate limiting step of the oxidative coupling of methane over silver is the diffusion of bulk-dissolved oxygen to silver (111) surfaces at which oxygen rapidly reacts with methane.

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Splitting of platinum crystallites supported on thin, nonporous alumina films

Cited by 93 publications

References 5 publications

Modeling of sintering and redispersion of supported metal catalysts

Modeling of sintering and redispersion of supported metal catalysts

Metal Redispersion Strategies for Recycling of Supported Metal Catalysts: A Perspective

High temperature partial oxidation reactions over silver catalysts

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