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根据α-Fe晶格参数,表面原子的配位不饱和性,反应的动力学几何因素,络合催化原理,以及由表面原子剩余杂化轨函所组成的基函的量子化学近似计算,本文提出N_2的端基吸附不是目前一般认为的垂直吸附在(111)晶面的底端原子上,而是N_2端基吸附在(111)晶面配位较底端原子不饱和的一个表面原子上,端基吸附与(111)面斜交约20°角,同时有三个与N_2分子中心相距约2.48A的最邻近铁原子侧基络合,生成端基加三侧基ω1,μ_3(η~2)型络合物。氨合成铁催化剂活性中心,除了这样的4-Fe原子簇吸附中心外,还需要一个和吸附中心毗邻并合用二原子的4-Fe原子簇氮分子离解中心,共构成6-Fe原子簇活性中心。本文提出的活性中心模型及吸附态,解释了H_2在铁屑上及钼屑上的吸附场电子发射显微镜图象(Brill et al.,＆ Ishizaka et al.);N_2或NH_3对催化剂预处理所引起的Mossbauer谱图象改变及氨合成活性的增加(Boudart et al.);N_2在Fe上的X光光电子能谱(Kishi et al.);说明了由场离子质谱证实的N_3~+,N_4~+的生成机理(Schmidt);~(14)N_2-~(15)N_2在Fe,Fe-Al_2O_3-K_2O上同位素交换机理,提出N或NH的表面迁移是同位素交换决定性步骤,从而解释了在Fe,Fe-Al_2O_3-K_2O上及H_2存在下同位素的显著差异及交换动力学(Ozaki et al.)。 ω_1,μ_
Based on the lattice parameters of α-Fe, the coordination of surface atoms, the kinetic geometry, the catalytic principle of complexation, and the quantum chemical approximation of the basis function composed of the surface hybrid atoms, It is suggested that the terminal adsorption of N 2 is not considered to be vertically adsorbed on the bottom atom of the (111) plane, but the N 2 terminal group is adsorbed on a surface atom whose (111) plane coordinates more unsaturated than the bottom atom , The terminal groups adsorbed on the (111) plane were inclined by about 20 ° and three adjacent side groups of the iron atom were located near the center of N_2 complexed to form terminal groups ω1 and μ_3 (η ~ 2) type complex. In addition to such a 4-Fe cluster center, an ammonia synthesis iron catalyst active center needs a nitrogen atom dissociation center of 4-Fe cluster adjacent to the adsorption center and a combination of two atoms to form a 6-Fe cluster active center . The proposed model for the active center and adsorption states explain the electron field emission microscopy image of H 2 on iron filings and molybdenum chips (Brill et al., & Ishizaka et al.). The effects of N 2 or NH 3 on the catalyst pretreatment (Boudart et al.); X-ray photoelectron spectroscopy of N_2 on Fe (Kishi et al.); Elucidation of N_3 ~ +, N_4 ~ (15) N_2- ~ (15) N_2 on Fe, Fe-Al_2O_3-K_2O, suggesting that the surface migration of N or NH is the decisive step of isotopic exchange, Significant Differences in Isotopes and Exchange Kinetics on Fe, Fe-Al_2O_3-K_2O and H_2 (Ozaki et al.). ω_1, μ_