A density functional theory study on adsorption and decomposition of acetic acid over silicon carbide nanotubes

Abstract

In this study, the adsorption behavior of acetic acid (CH3COOH, AC) over (6,0) zigzag silicon-carbide nanotube (SiCNT) surface are investigated by carrying out density functional theory calculations. The structures of AC-SiCNT complexes are optimized and characterized by frequency calculations at the M06-2X/6-31G* computational level. To understand the catalytic activity of the surface, the interaction between the AC and SiCNT is analyzed by detailed electronic analysis such as adsorption energy (Eads), density of states (DOS), electron density difference and activation barrier. The calculated Eads values are in the range of −0.55 to −3.56eV. In order to investigate the curvature effect on the adsorption energies of the AC molecule, the AC adsorption on (5,0) and (7,0) SiCNTs is also studied. Our results indicate that the AC adsorption over the narrower (5,0) SiCNT is more thermodynamically favorable process than (6,0) one. So it seems that the curvature of small-diameter SiCNTs facilitates the sp3-hybridization of Si atoms and thus helps in the binding of AC on the tube surface. For the gas-phase AC decomposition over the SiCNT, the reaction proceeds through an acetate mechanism, which is consistent with the experimental results obtained on metal or metal oxide surfaces.