Density functional theory molecular simulation of thiophene adsorption on MoS2 including microwave effects

Hydrodesulfurization (HDS) is an important catalytic process in the oil industry used to remove sulfur from petroleum fractions, thus producing cleaner fuels. Molybdenum sulfide catalysts are extensively used in this process. In particular, thiophene adsorption, a first step of HDS process, is a prototype system for theoretical investigations. In this work, density functional theory (DFT) calculations of thiophene adsorption on MoS2, using a Mo16S32 cluster, were done. A distributed multipole analysis provided values of charges, dipole and quadrupole moments on atomic sites of the thiophene molecule and the Mo16S32 cluster, before and after adsorption. Harmonic vibrational frequencies were also computed. These data were used to discuss the adsorption process and to qualitatively investigate patterns of microwave absorption on this system, a possible way of accelerating the rate of HDS process. It was verified that permanent site dipoles would be the main effect responsible for dielectric heating. In particular, the distributed multipole analysis presented appreciable values of the permanent dipole moment values at atomic sites of the cluster active region and at the adsorbed thiophene. These results indicate differential heating properties at the atomic level when microwave heating is used, which are theoretically shown here for the first time. Therefore, theoretical evidences on the existence of hot spots are provided, which were only previously implied experimentally.