Abstract: The relationship of surface active site and turnover frequency versus activity for ammonia synthesis catalyst which were obtained from different iron oxide as precursor were investigated by means of a physisorption of N 2 and a chemisorption of CO and CO 2 and activity test.The exposure percent of active iron atom on the surface was lower than one percent, which indicates that more than 99% of the iron atom were buried in the internal of catalyst.The change of activity,specific rate,turnover frequency,acid coverage and the coverage ratio of acidic to alkalic surface area had a similar regularity with the change of the state and the composition of iron oxide precursor of catalyst. With increased FeO content,the surface properties and surface structure of the reduced catalyst were changed,and the number of active site was decreased and the intensity (TOF) of active site was increased.FeO might be advantageous to the formation of FeAl 2O 4 iron aluminate in the presence of Al 2O 3,and surface restracturing of FeAl 2O 4 to iron crystal face increased the activity of catalyst.

摘要： 采用N2 低温吸附、CO和CO2 化学吸附技术和活性试验研究了不同铁氧化物为母体的氨合成催化剂表面活性位与催化活性的关系 .结果表明 ,活性相铁原子在表面的暴露百分数 <1 % ,99%以上的铁原子掩埋在体相内部 .随着母体铁氧化物性质和组成的变化 ,催化剂活性 (以氨的体积分数表征 )、质量反应速率 (rm)、合成氨转换频率 (TOF)和表面酸覆盖度 (SA)及其酸碱覆盖度的比例 (SA/SK)有相似的变化规律 ,即与Fe2 +/Fe3+呈驼峰形变化曲线 .实验发现 ,随着母体中FeO含量的增加 ,还原后催化剂表面性质和表面结构改变 ,表面活性位数目减少而活性位强度增大 .这可能是结构改性剂Al2 O3对Fe晶面的表面重构作用所致 .