Promoting effect of Ni on the structure and electronic properties of NixMo(1−x)S2 catalyst and benzene adsorption: A periodic DFT study

Abstract

Aromatic hydrogenation (e.g., benzene) over MoS2-based catalyst harbours essential importance in hydrotreating process due to stringent environmental and fuel requirement. In this work, the promoting effect of Ni on structure and electronic properties of NixMo(1−x)S2(1 0 0) surface (x = 0, 0.25, 0.5, 1.0) and benzene adsorption has been investigated by DFT calculations using PW91-OBS and PW91 functions. It is found that the adsorption of benzene requires at least three coordinatively unsaturated sites (CUS), which can improve the activation of CC bond. The introduction of Ni facilitates the formation of stable CUS sites, and enhances the eletrophilicity of the Mo atoms for adsorption. Furthermore, the volcanic-shape relationship between Ni content and benzene adsorption ability is then established. With the increase of Ni percentage from 0 to 50%, the adsorption energy and electrons transferred from benzene molecules to the surface gradually increase due to the increased ligand effect for Mo atoms. However, overmuch Ni leads to the sharp decrease of benzene adsorption energy. Dispersion correction analysis indicate that the interplay between benzene and Ni is dominated by weak vdW interactions. The results reported herein are beneficial to the design of efficient NiMoS2 catalysts for hydrotreating.