On the aging of supported metal catalyst due to hot spots

✍ Scribed by E. Ruckenstein; C.A. Petty

• Publisher: Elsevier Science
• Year: 1972
• Tongue: English
• Weight: 837 KB
• Volume: 27
• Category: Article
• ISSN: 0009-2509
• DOI: 10.1016/0009-2509(72)80008-3

✦ Synopsis

Aging of supported metal catalyst because of sintering of small crystallites is primarily controlled by the high temperatures achieved on the crystallite sites because the heat of reaction per molecule is released in a very short time. The overall rate of the sintering process is determined by a relatively slow cascade mechanism of successive rapid heatings followed by the detachment of clusters of platinum atoms and their mobility over the support.

Because a hot spot is generated during a time on the order of lo-j3 sec. and the relaxation time of the heat flux is of the same order or larger, the finite propagation velocity of the heat flux must be taken into account in the description of the temperature field. The conclusion is reached that the temperature achieved near the reaction surface is much higher than that resulting from Fourier's law and that the cooling of the hot spot after the completion of a reaction is so hindered that the high temperature lasts sufficiently long for detachments of clusters of atoms to take place.

A lower bound is established for a stable distribution of particle sizes.