MoCo and MoWNi Clusters as Models for Hydrodesulfurization: A DFT Study of the Geometric, Electronic, and Magnetic Properties of Mo_mCo_n (3 ≤ m + n ≤ 8) and Mo_xW_yNi_z (3 ≤ x + y + z ≤ 8) Clusters

Abstract

The geometric, electronic, and magnetic properties of Mo m Co n (3 ≤ m + n ≤ 8) and Mo x W y Ni z (3 ≤ x + y + z ≤ 8) clusters, as models for the hydrodesulfurization process, are investigated from a computational point of view. Optimized geometries of stable MoCo isomers show that Mo and Co atoms tend to segregate from each other. Charge transfer occurs from Mo to Co. Optimized geometries of stable MoWNi isomers display MoW cores with Ni atoms decorating triangular faces. Charge transfer takes place from W atoms to Mo and to Ni atoms. Various aggregates are identified as candidates to participate in the hydrodesulfurization process according to the change in Mulliken atomic charges after the removal and the addition of an electron to neutral clusters. For MoCo species, it is found that both Mo and Co atoms would be involved in the active sites of the catalyst. For MoWNi clusters, instead, the active sites of the catalyst would be formed by Mo and W atoms exclusively, whereas the Ni atom would be responsible for modifying the local electronic structure of Mo and W atoms.