Abstract:

Density functional theory wB97XD method, RDG function method and counterpoise correction theory were used to study adsorption characteristics of N₂ on shale kerogen C₂₈H₁₄O and nitrogen-doped shale kerogen C₂₇H₁₄ON. It shows that the active adsorption site is located on the central position above the benzene ring for N₂ adsorbed on both kerogen C₂₈H₁₄O and nitrogen-doped kerogen C₂₇H₁₄ON. The adsorption energy is in the range of 8~10 kJ·mol^-1, which shows that the main interaction between nitrogen molecule and kerogens is van der Waals interaction and steric repulsion. Nitrogen doping changes the geometric configuration and electron cloud distribution of kerogen. As a result, the nitrogen-containing heterocycle is no longer a stable active site. The adsorption energy is a little lower than that of N₂ adsorbed on C₂₈H₁₄O, but it is still in the range of 8~10 kJ·mol^-1. The main interaction force between N₂ and C₂₇H₁₄ON is still van der Waals interaction and steric repulsion. This work is significant for understanding adsorption characteristics of small molecules on kerogens. It provides theoretical support for the exploring of shale gas.

Key words: shale gas, kerogen, adsorption, wB97XD, RDG function