Visualizing the mobility of silver during catalytic soot oxidation

• Silver particles exhibit significant mobility during catalytic soot oxidation due to attractive forces between the metal and the moving carbon oxidation front.
• Mobility ensures the constant presence of a reactive carbon–silver–oxygen interface during oxidation.
• Smaller silver particles show mobility at lower temperatures due to their lower internal cohesive energy and are hence able to catalyze more efficiently soot oxidation at lower temperatures.

The catalytic activity and mobility of silver nanoparticles used as catalysts in temperature programmed oxidation of soot:silver (1:5 wt:wt) mixtures have been investigated by means of flow reactor experiments and in situ environmental transmission electron microscopy (ETEM). The carbon oxidation temperature was significantly lower compared to uncatalyzed soot oxidation with soot and silver loosely stirred together (loose contact) and lowered further with the two components crushed together (tight contact). The in situ TEM investigations revealed that the silver particles exhibited significant mobility during the soot oxidation, and this mobility, which increases the soot/catalyst contact, is expected to be an important factor for the lower oxidation temperature. In the intimate tight contact mixture the initial dispersion of the silver particles is greater, and the onset of mobility occurs at a lower temperature which is consistent with the lower oxidation temperature of the tight contact mixture.

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