Sintering and Redispersion

Stevenson S, Dumesic JA, Baker RTK, Ruckenstein E (1987) (eds) Metal-support interactions in catalysis, sintering and redispersion. Van Nostrand Reinhold, New York Ferrari AM, Neyman KM, Mayer M, Staufer M, Gates BC, ROsch N (1999) J Pbys Chem B 103 5311... 

Stevenson, S.A., Dumesic, J.A., Baker, R.T.K. and Ruckenstein, E. (1987) Metal-Support Interactions in Catalysis, Sintering and Redispersion, Van Nostrand Reinhold, New York. 

The preparation of real supported catalysts will involve the deposition of a precursor salt followed by decomposition and/or reduction to the final metallic state. We shall consider the influence of the precursors and the effect of oxidative pretreatments later. First, we consider how the shapes of supported metal particles will vary with time under reducing conditions, since this represents the working condition for most metal catalysts. A comprehensive review of sintering and redispersion in supported metals has been presented by Ruckenstein and Dadyburjor.232... 

Studies of sintering and redispersion of supported metal catalysts have been reviewed by several authors [M8] most of these reviews focus on early kinetic studies of sintering of supported metal catalysts using a simplified power law expression (SPLE). Unfortunately this crude approach does not permit sintering kinetics to be presented in a consistent way nor does it enable (1) useful extrapolation of the data to other conditions (2) useful quantitative comparisons between different studies, or (3) physically meaningful kinetic parameters to be obtained. The ultimate result has been confusion regarding the effects of reaction parameters such as atmosphere and temperature and of catalyst properties such as support promoters, etc., on sintering rates. 

From previous experimental studies of sintering [2,9 11 12] it is evident that sintering and redispersion are strong functions of temperature time atmosphere and support. Sintering/redispersion rates are also significantly affected by choice of metal and/or promoter metal loading, and catalyst preparation. The discussion below of previous work will focus on how sintering rates are affected by these variables. 

R.T.K. Baker, C.H. Bartholomew, and D.B. Dadyburjor, in J.A. Horsley (Editor and Project Leader), Stability of Supported Catalysts Sintering and Redispersion, Catalytic Studies Division, 1991. 

C.H. Bartholomew, "Model Catalyst Studies of Supported Metal Sintering and Redispersion Kinetics," Catalysis, Specialist Periodical Report, Royal Society of Chemistry, Thomas Graham House, Cambridge, UK, Vol. 10,1992,... 

Since the atomic migration and crystallite migration mechanisms have been amply discussed in the previous proceedings on Catalyst Deactivation, the emphasis of the present paper is on the wetting and spreading phenomena, which appear to play a major role in sintering and redispersion. 

It is clear that wetting and spreading phenomena are significantly involved in all steps indicated in Fig. 3. Rather than report on the many studies on sintering and redispersion in practical supported metal catalysts, the following discussion briefly highlights some model studies which have been nicely reviewed by Rucken-stein et al. [1],... 

E Ruckenstein in S A Stevenson, J A Dumesic, RTK Baker, E Ruckenstein, Metal-Support Interactions m Catalysis, Sintering, and Redispersion, Van Nostrand Reinhold, New York, 1987, pp 156, 187... 

Recent experiments have revealed that both sintering and redispersion are much more complex phenomena than previously considered. Transmission electron microscopy experiments (12) have Indicated that during heating in oxygen, Rd crystallites extend on alumina substrate, change their shape, and exhibit tearing and fragmentation. There is also experimental evidence that for... 

E. Ruckenstein,in Metal-Support Interactions In Catalysis, Sintering and Redispersion, (Stevenson, Dumesic, Baker, Ruckenstein Eds,), Van Nostrand Reinhold, N Y, 1987 p. 140. 

Model Catalyst Studies of Supported Metal Sintering and Redispersion Kinetics ... 

What are the principal fundamental mechanisms by which thermal degradation, sintering and redispersion of supported metals occur What factors determine which of these mechanisms predominates or controls the sintering process What do we leam from model catalyst studies regarding these mechanisms ... 

During the past two decades, sophisticated microscopic and spectroscopic techniques have been aj lied to the investigation of sintering and redispersion of model film and single crystal metal-support systems. This review presents and discusses results obtained in these investigations with an emphasis on mechanistic evidence. 

Studies of sintering and redispersion involving model catalysts reported through 1980 were reviewed by Wanke and Bolivar. A list of these and more recent studies through 1991 are provided in Table 2. Most of these were electron microscopy studies of alumina-su rted Ni, Fe, Pd, and Pt, although a few other metals (Co, Ir, Rh), bimetallics (of Co, Fe, Ni, Pd, Rh, and Pt), and supports (silica, titania, and carbon) are represented. 

Effects of Atmosphere and Temperature on Sintering and Redispersion of Supported Model Catalysts... 

Kinetics of Sintering and Redispersion Modd-Supported Metals... 

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