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

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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).