CONTROL OF A BIPHASIC SURFACE-REACTION BY OXYGEN COVERAGE - THE CATALYTIC-OXIDATION OF AMMONIA OVER PT(100)

被引:143
作者
BRADLEY, JM [1 ]
HOPKINSON, A [1 ]
KING, DA [1 ]
机构
[1] UNIV CAMBRIDGE,DEPT CHEM,CAMBRIDGE CB2 1EW,ENGLAND
关键词
D O I
10.1021/j100046a032
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 ammonia oxidation reaction on Pt{100} has been investigated over the temperature range 300-800 K, using molecular beams under UHV conditions. The reaction is biphasic, with N-2 being the major product below 600 K and NO being the major product above 600 K, It is found that product selectivity can be controlled by varying the beam composition as well as by varying the surface temperature. The efficiency of the reaction to NO can be significantly increased by preadsorption of oxygen on the crystal. Coadsorption and isothermal experiments translate the beam composition dependence into a surface oxygen coverage dependence, with high oxygen coverages resulting in the suppression of N-2 production. N-2 is believed to be produced mainly from the dissociation of NO produced by oxidation of adsorbed NH3. The observed oxygen coverage dependence of product formation is explained by a sharp fall in the heat of adsorption of the dissociated N(a) and O(a) with increasing O(a) coverage. At high surface oxygen coverages the suppression of N-2 production arises from the resulting inhibition of NO dissociation. The observed surface temperature dependence of product formation is explained by competition between NO desorption and NO dissociation.
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收藏
页码:17032 / 17042
页数:11
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