Adsorption thermodynamics of sulfur- and nitrogen-containing molecules on NiMoS : a DFT study

Detailed adsorption thermodynamic data of organosulfur and organonitrogen molecules on NiMoS hydrotreating catalyst active sites were studied by density-functional theory (DFT) calculations. Initially, the adsorption of the molecules on the NiMoS edge surface is studied, and the most stable configuration for each molecule is identified. The changes in electronic energy and zero point vibrational energy upon the adsorption of different molecules on the NiMoS surface are calculated. The contribution of adsorbed molecules, as well as gas phase molecules, to changes in entropy and Cp values are obtained by calculating vibrational frequencies of adsorbed and free molecules. With these data, the changes in enthalpy, entropy, and free energy due to the adsorption on the NiMoS edge surface at different temperatures are determined. These data can be used to estimate the relative surface coverage of each type of species at different reaction conditions.