Palladium Catalyzed Oxidation of Amorphous Carbon: A Study by in Situ Transmission Electron Microscopy

✍ Scribed by H.-I. Su; K. Heinemann; H. Poppa; M. Boudart

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 837 KB
• Volume: 106
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1264

✦ Synopsis

Palladium clusters, (10-30 \mathrm{~nm}) in size, were grown in UHV on amorphous carbon in a transmission electron microscope (TEM). The Pd catalyzed oxidation of carbon was then followed in situ in the TEM between 720 and (800 \mathrm{~K}) at a pressure (p) of (\mathrm{O}{2}) with (\left.0.25<p\left(10^{-4} \mathrm{mbar}\right)<1.0\right)). The behavior of hundreds of individual clusters was recorded on videotape in real time. Clusters moved as they dug irregular channels throughout the carbon film. They exhibited liquid-like behavior and frequent change of contrast (flashing). These active clusters started to move after an induction period. Some clusters remained inactive. Active clusters coalesced with inactive clusters to form active clusters. After some time, active clusters became and remained inactive. The site time yield of catalyzed oxidation, defined as the number of (\mathrm{C}) atoms reacting per exposed (\mathrm{Pd}) atom per second was almost independent of temperature and proportional to pressure of (\mathrm{O}{2}). Under the conditions of this work, it appears that the rate determining step of the oxidation of carbons is the dissociative chemisorption of (\mathrm{O}{2}) on (\mathrm{Pd}), with every (\mathrm{O}{2}) molecule sticking to the (\mathrm{Pd}) surface reacting to (\mathrm{C}) with formation of (\mathrm{CO}_{2}). 1993 Academic Press, Inc.