Modeling metal adsorption at amorphous silica: Gold atoms and dimers as example

Study on syngas methanation mechanism over Ni4/MCM-41 catalyst based on density functional theory

The density functional theory method is employed to systematically explore the mechanism of syngas methanation on the Ni4/MCM-41 catalyst surface. The calculation results show that the optimal pathway of CH4 formation is CO + H → CHO + H → CH2O + H → CH3O → CH3 + H → CH4 with the rate-determining step of CH3O direct dissociation. Because the activation energy for the direct dissociation of CH3O species is much lower than that for the CH3OH formation (198.6 vs 264.8 kJ mol−1), there is almost no by-product CH3OH that appeared in the products of the syngas methanation over the Ni4/MCM-41 catalyst. Compared with other conventional nickel-based methanation catalysts, Ni4/MCM-41 catalyst is an excellent methanation catalyst with high selectivity of CH4.

Dynamics of ultrathin gold layers on vitreous silica probed by density functional theory

Ab initio molecular dynamics simulations demonstrate substantial differences in Au agglomeration behavior on hydroxyl-free and hydroxylated vitreous silica surfaces.

Density functional model studies of uranyl adsorption on (001) surfaces of kaolinite

The adsorption of uranyl on two types of neutral (001) surfaces of kaolinite, tetrahedral Si(t) and octahedral Al(o), was studied by means of density functional periodic slab model calculations. Various types of model surface complexes, adsorbed at different sites, were optimized and adsorption energies were estimated. As expected, the Si(t) surface was found to be less reactive than the Al(o) surface. At the neutral Al(o) surface, only adsorption at protonated sites is calculated to be exothermic for inner- as well as outer-sphere adsorption complexes, with monodentate coordination being preferred. Adsorption energies as well as structural features of the adsorption complexes are mainly determined by the number of deprotonated surface hydroxyl groups involved. Outer-sphere complexes on both surfaces exhibit a shorter U-O bond to the aqua ligand of uranyl that is in direct contact with the surface than to the other aqua ligands. This splitting of the shell of equatorial U-O bonds is at variance with common expectations for outer-sphere surface complexes of uranyl.