無電解析出プロセスにおける還元剤BH₄^－に対するCu及びPd表面の触媒作用機構の理論的解析

抄録

To elucidate the catalytic reaction mechanism of BH₄^－ (a reducing agent) on metal surfaces during electroless deposition, its oxidation reaction was investigated theoretically using density functional theory (DFT) calculation. Particularly in this study, dehydrogenation reaction of BH₄^－ was modeled and analyzed because it is the most important elementary step of overall oxidation for the catalytic behavior of metal surfaces. To ascertain the tendencies of catalytic activity of metal surfaces, the reaction on Cu(111) and that on Pd(111) were compared. Actually, Cu shows little catalytic activity toward BH₄^－ oxidation, whereas Pd shows strong catalytic activity. Results of reaction energy calculations show that the BH₄^－ dehydrogenation occurs with difficulty on Cu(111), but it occurs easily on Pd(111), which corresponds to experimental results. Detailed analyses of reaction system electronic structures show that the d-band states of each surface are important to assess the background of the difference. Because the Pd surface has a high-energy d-band, it can interact with high-energy unoccupied orbitals of BH₄^－, leading to electron donation from the surface toward BH₄^－. This electron donation effect from Pd provides dissociation activity of the B-H bond, which promotes dehydrogenation of BH₄^－.