A DFT study of site-dependent energetics of hexagonal MoS2 nanoparticles under varying reaction conditions

A plane wave periodic density functional theory study of a representative hexagonal shaped MoS2 nanoparticle is conducted to compute the site-dependent energetics of the catalyst under different operating conditions. It is shown that the (1) energy for vacancy formation and the associated free energy profile of the reaction steps involved in creating the vacancy and (2) the binding energy of hydrogen and other probe atoms such as CO and lutidine, are all dependent on the location of the associated sulfur or molybdenum atom and the edge type (i.e. metal or sulfur edge). In particular, sulfur atoms near the corner are more strongly bound than those in the interior of the metal edge. Further, a larger metal-sulfur bond strength results in lower binding energy of hydrogen on that sulfur atom which in turn implies that this hydrogen is more Brønsted acidic in nature. These results indicate that the nature and the location of active sites on MoS2 is heavily dependent on the nature of the reaction that is being catalyzed and the corresponding operating conditions.