A comparison of the NO–CO reaction over Rh(100), Rh(110) and Rh(111) |
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Authors: | GS Herman CHF Peden SJ Schmieg DN Belton |
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Affiliation: | (1) Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, PO Box 999, MSIN K8‐93, Richland, WA 99352, USA;(2) Physical Chemistry Department, General Motors Research and Development Center, 30500 Mound Road, Warren, MI 48090‐9055, USA |
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Abstract: | Reaction rates and product selectivities were measured over the Rh(100) surface as a function of temperature, and CO and NO
partial pressures. These results are compared with our prior studies of the NO–CO reaction on the Rh(111) and Rh(110) surfaces.
The only products detected for all three surfaces were CO2, N2O, and N2. Furthermore, for the Rh(100) surface we have found a significant change in the apparent activation energy (E
a) with reaction temperature. For the Rh(100) surface it was found that the E
a can change by a factor of 2.3 in the temperature range investigated here, from 528 to 700 K, with the lower values obtained
at higher temperatures. In contrast, E
a's were found to remain constant over the same temperature range for the Rh(110) and Rh(111) surfaces. The results observed
for the Rh(100) surface suggest that reaction kinetics are dominated by variations in NO coverages. At low temperatures, the
surface is fully saturated with NO, and dissociation is limited by the availability of vacancy sites through NO desorption.
At high temperatures, the surface is still primarily covered with NO, however, the number of vacancy sites has increased substantially.
In this case, we propose that the apparent activation energy is now reflecting NO dissociation kinetics rather than those
for NO desorption.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | NO– CO reaction rhodium NOx reduction structure sensitive reaction |
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