ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The spatial distributions of NO, N2, and N2O desorbing from Pd(211), Pd(S)-[3(111)×(100)], in temperature programmed desorption (TPD) and that of N2 produced in the temperature programmed reaction (TPR) of NO+H2 have been studied. The spatial distribution of N2 desorbing at 510 K in the TPD had a maximum intensity at θ=−25–−30 deg (down the steps) in the [1 1¯ 1¯] direction, which is almost normal to the (100) steps, and is described by 2.4 cos12(θ+26 deg). Taking account of the fact that NO molecules are preferentially adsorbed on the (111) terraces of a Pd(211) surface at low coverage, it is deduced that the NO adsorbed on the (111) terraces undergoes migration to the (100) steps, where N2 is produced. An isotopically labeled angle-resolved TPD experiment showed that N2 was produced by the NO+N reaction. On the other hand, the desorption of NO is normal to the crystal surface. This phenomenon indicates that NO desorbs via a predesorption state, where NO molecules forget their memory of the previous adsorption sites. In contrast, the spatial distribution of N2 given by the catalytic reaction in a flow of NO+H2 at 650 K, was completely different from that of N2 produced by NO+N reaction at around 500 K. It is concluded that the spatial distribution reflects the reaction or desorption mechanisms, especially the reaction coordinate on the surface. © 1999 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.478608
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