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合成气甲烷化这一过程是从合成气在金属表面的吸附开始的,但Ni基催化剂与气体的作用机理受实验条件的限制尚未能达成共识,所以有必要从原子尺度运用模拟方法来了解这个动态过程,从而优化催化剂及反应条件。本文采用密度泛函理论首次计算模拟了H2以不同方式和Nin(n=1-13)团簇作用的情况。对吸附能、净电荷及结构参数的分析表明:H2分子的H-H键平行接近于Ni团簇的顶点位时为分子态的非解离吸附,H-H键长从0.862到0.908,对比吸附前的键长0.750都有所增长,吸附能从-40 k J/mol到-80 k J/mol;作用于桥位和空穴位时,解离不需要活化,即为原子态吸附,吸附能范围从-61.87 k J/mol到-120.68 k J/mol。而H2分子以H-H键竖直方式作用于Ni团簇时,过渡金属Ni对H2的吸附活化作用很小,为物理吸附。可见,H2以H-H键平行还是竖直方式作用于团簇的何位点决定了吸附的类型,这成为Ni对H2活化作用强弱的关键;气体在催化剂表面的扩散对形成稳定的原子态吸附有利;H2被催化剂Ni活化后主要以原子态形式存在,这为探索甲烷化机理提供了理论依据。
Syngas methanation begins with the adsorption of syngas on the metal surface. However, the mechanism of interaction between the Ni-based catalyst and the gas has not been agreed upon by the experimental conditions, so it is necessary to use simulation from the atomic scale to understand This dynamic process optimizes the catalyst and reaction conditions. In this paper, the first calculation of the density functional theory simulates H2 in different ways and Nin (n = 1-13) cluster effect. The analysis of the adsorption energy, the net charge and the structural parameters showed that the HH bonds of H2 molecules were close to the peak positions of Ni clusters in molecular non-dissociative adsorption. The HH bond lengths ranged from 0.862 to 0.908. Compared with those before adsorption The length of 0.750 increases with the adsorption energy ranging from -40 k J / mol to -80 k J / mol. When acting on the bridging and cavitating sites, the dissociation does not need to be activated, that is, atomic state adsorption. The adsorption energy ranges from - 61.87 kJ / mol to -120.68 kJ / mol. The H2 molecule H-H bond vertical role in the Ni cluster, the transition metal Ni on the adsorption of H2 activation is small, physical adsorption. It can be seen that the site of H2 acting parallel or vertically on HH bonds determines the type of adsorption, which becomes the key to the activation of H2 on Ni. The diffusion of gas on the surface of catalyst can form stable atomic state adsorption It is favorable for H2 to be mainly in the atomic state after being activated by the catalyst Ni, which provides a theoretical basis for exploring the methanation mechanism.