DFT investigation of MoS 2 nanoclusters used as desulfurization catalysts

Supported single‐layer MoS 2 is a well‐established catalyst used by the petroleum industry to remove sulfur from fossil fuels. It is believed that the catalytic activity occurs at the edge of the MoS 2 nanoparticles. Recently, atomic‐scale images of MoS 2 nanoclusters under catalytic working conditions have been obtained with scanning tunneling microscopy (STM). These images show that certain triangular‐shaped “magic clusters” are formed, where the triangular shape is attributed to stabilization from excess sulfur at the cluster edges. Much of the recent theoretical rationalization of the MoS 2 cluster structures has been formulated by using plane‐wave DFT calculations. However, the clusters observed in the recent STM images are small enough that their structures and properties can be evaluated using direct space DFT calculations. We present the theoretically optimized structures obtained with DFT calculations for the series of Mo 10 S x clusters with x = 12, 18, 24, 30, and 36. From consideration of their relative energies and simulated STM images, we find the cluster with the Mo 10 core most likely being imaged in the STM experiments is the Mo‐edge cluster Mo 10 S 24 . This contrasts with the assignment to the S‐edge cluster Mo 10 S 24 by the experimentalists and their suggestion that Mo‐edge clusters are less favored than S‐edge clusters when there are 21 or less Mo atoms. Furthermore, despite being able to build initial Mo 10 S x structures with a high degree of symmetry, we find the fully optimized Mo 10 S x clusters to have essentially no symmetry, and we discuss how this could be playing a role in the MoS 2 catalytic activity. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009