Theoretical studies of the alkali atoms on the Fischer-Tropsch reaction.

众所周知，在过渡金属催化剂中添加碱原子可以促进甲烷化反应和费托合成。在本研究中，我们试图阐明：a)过渡金属与碱原子之间的稳定机理，b)过渡金属与CO分子之间的稳定机理，以及c)过渡金属中CO与碱原子之间的稳定机理，用小的铜团簇代替过渡金属。所采用的方法是从头算、SCF和CI计算。我们已经完成了其中的两个((A)和(B))。在a)中发现了两种类型的吸附。一种是电荷转移型吸附，大量的Na3S电子进入铜团簇。另一种是非电荷转移类型，其中Na原子几乎保持在其基态，铜团簇也是如此。前者比后者获得更大的稳定性(见参考文献1)。我们有一定的信心，认为小团簇可以模拟大块金属的某些特性，如态密度(见文献[1])。2、3、4)。因此，我们挑战于分析在低覆盖度的Na上观察到的铜(111)上的电子能量损失谱(EELS)，并在团簇计算的基础上成功地分析了EELS(见参考文献)。5)。对于b)，揭示了CO在铜团簇上稳定的原因。利用Cu4CO和Cu5CO的激发能归属了CO在块体铜上的吸收光谱。6和7)。文献[1]对铜-甲烷相互作用进行了研究。8)。

It is well known that alkali atoms added to transition metal catalysts promote the methanation reaction and Fischer-Tropsch syntheses. In this study we intended to clarify, a) the mechanism of the stabilization between transition metals and a alkali atom, b) that between the transition metals and the CO molecule, and c) that among the transition metals, CO, and a alkali atom, using small copper clusters as a substitute of transition metals. The method employed were ab initio SCF and CI calculations. We have completed two ((a) and (b)) of them. In a) two types of adsorption were found. One of them is a charge transfer type adsorption where a fairly large number of Na 3s electrons moves into copper clusters. The other is a non charge transfer type where the Na atom remains almost at its ground state and so do copper clusters. The former gets larger stabilization than the latter (See Ref. 1). We have some confidence that the small clusters can simulate some characteristics the bulk metals such as density of the states (See Ref. 2,3,4). We, therefore, challenged to analyzethe electron-energy-loss-spectra (EELS) observed on low-coverage Na on Cu (111) and EELS are successfully analyzed on the basis of the cluster calculation (See Ref. 5). For b), the origin of the stabilization of CO on the cu cluster was revealed. The adsorption spectra of CO on the bulk Cu were assigned by the use of the excitation energies of Cu_4CO and Cu_5CO (See Refs. 6 and 7). A study on Cu-CH_2 interaction was given in Ref. 8).