The Theoretical Investigation of the Promotion of K on Chemisorbed CO on Ni（100）

The coadsorption of K and CO on Ni（100） has been investigated using SCC-DV-X_α quantum chemistry calculation. Three models are designed to investigate the mechanism of K promoter on chemisorbed CO. The calculation shows that the increase of local electron density of Ni（100） doesn’t lead the activation of CO obviously. The promotion of K on CO mainly result from a through-space electrostatic interaction which makes electron transfer in the form of K→Ni→CO. As a result, the number of electrons on CO 2π^* increases and CO is activated. Since the overlap populations betwee K and C, K and O are 0.005 and 0.004 respectively, it’s concluded that there is no strong chemical interaction between K and CO. There is CO^δ>-…K^δ+ionic complex on the surface of Ni（100）. With the adsorption of CO on Ni（100）, the electrons on CO 5σ orbital will repulse with the electrons on σ space of Ni（100） and the electrons of 5σ move from C to O. However, the electrons of CO 4σ and 1π orbitals move from O to C. Corresponding to such kind of movement of electrons, 4σ contributes more than 5σ in the bonding between Ni and CO. The form of hybridization of carbon in 5σ will change from sp to sp to sp².Also, the coadsorption of K makes the ionic potentials of CO 4σ, 5σ and 1π increase from 9.88eV. 7.34eV and 6.83（6.81）eV on CO/Ni（100） to 10.18eV 7.86eV and 7.29（7.24）eV on CO / K / Ni（100）, respectively.