The adsorption and decomposition of NO on Pd(110)

被引:65
作者
Sharpe, RG
Bowker, M
机构
[1] UNIV READING, DEPT CHEM, READING RG6 6AD, BERKS, ENGLAND
[2] UNIV LIVERPOOL, IRC SURFACE SCI, LIVERPOOL L69 3BX, MERSEYSIDE, ENGLAND
关键词
chemisorption; low index single crystal surfaces; molecule-solid reactions; nitrogen oxides; palladium; sticking; surface chemical reaction;
D O I
10.1016/0039-6028(96)00604-8
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The sticking probability of nitric oxide (NO) on Pd(110) and the relative selectivity of the surface to nitrogen (N-2) and nitrous oxide (N2O) production has been measured as a function of coverage and as a function of surface and gas temperatures using a molecular beam. It is found that, at low temperatures (<440 K), molecular adsorption occurs with an initial sticking probability of 0.40+/-0.02, rising quickly to a maximum of about 0.48+/-0.02 as coverage increases before falling towards saturation. Following adsorption at 170 K four distinct adsorption sites can be identified by subsequent TPD. Hence, if beaming occurs at a temperature above the TPD peak due to a given site, then that site cannot be populated and the saturation coverage is found to be reduced. At higher temperatures (440-650 K) the sticking probability is seen to decrease continuously as a function of coverage. At a given NO uptake, the sticking probability falls with temperature indicating that the rate of NO desorption is significant in this temperature range. In addition, dissociation occurs leading to the desorption of nitrogen and nitrous oxide leaving only oxygen adatoms on the surface. The oxygen adatoms poison further reaction but can be cleaned off, even at the lowest temperature at which dissociation occurs, by hydrogen or carbon monoxide, At the low temperature end of this range more nitrous oxide is produced than nitrogen but this ratio falls with temperature until, above 600 K, there is 100% selectivity to the production of nitrogen which we propose is due to the low lifetime of molecular NO on the surface. However, at such high temperatures, reaction only occurs on a few sites probably located at the few step edges present on the crystal.
引用
收藏
页码:21 / 30
页数:10
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