氨合成反应的BOC-MP法研究

BOC MP Study for Ammonia Synthesis

用键级守恒莫尔势函数法（ＢＯＣ－ＭＰ）研究了铁催化剂表面氨合成反应的缔合式和解离式两种机理，计算表明缔合式机理速控步骤的活化能垒Ｎ２，ａｄ＋Ｈａｄ→ＮＨａｄ＋Ｎ（９２ｋＪｍｏｌ－１）低于解离式机理速控步骤Ｎａｄ＋Ｈａｄ→ＮＨａｄ（１６３ｋＪｍｏｌ－１）的活化能垒，但反应Ｎ２，ａｄ→Ｎａｄ＋Ｎａｄ（５０ｋＪｍｏｌ－１）的活化能垒又明显低于缔合式途径速控步骤的活化能垒．由此可推断，在铁催化剂表面存在着两种氨合成竞争反应途径，但缔合式机理在反应能量学上较为有利．

Both mechanisms of ammonia synthesis, the associative and the dissociative, on iron catalysts are studied with the Bond order conservation Morse potential (BOC MP) approach. The calculations indicated that the activation barrier of the rate(determining step, N 2,ad +H ad NH ad +N ad (92 kJ mol -1 ) for the associative pathway is lower than that of the N ad +H ad NH ad (163 kJ mol -1 ) for the dissociative pathway. Howerver, the activation barrier for reaction, N 2,ad N ad +N ad (50 kJ mol -1 ) is lower more much than that of rate determining step, N 2,ad +H ad NH ad +N ad for the associative pathway. It is shown that there are two competitive reaction pathways for ammonia synthesis on iron catalysts but the associative pathway is more favorable in catalytic reaction energy.