Electron tomography and fractal aspects of MoS and MoS/Co spheres.

A study was made by a combination of 3D electron tomography reconstruction methods and N adsorption for determining the fractal dimension for nanometric MoS and MoS/Co catalyst particles. DFT methods including Neimarke-Kiselev's method allowed to determine the particle porosity and fractal arrays at the atomic scale for the S-Mo-S(Co) 2D- layers that conform the spherically shaped catalyst particles. A structural and textural correlation was sought by further characterization performed by x-ray Rietveld refinement and Radial Distribution Function (RDF) methods, electron density maps, computational density functional theory methods and nitrogen adsorption methods altogether, for studying the structural and textural features of spherical MoS and MoS/Co particles. Neimark-Kiselev's equations afforded the evaluation of a pore volume variation from 10 to 110 cm/g by cobalt insertion in the MoS crystallographic lattice, which induces the formation of cavities and throats in between of less than 29 nm, with a curvature radius r  < 14.4 nm; typical large needle-like arrays having 20 2D layers units correspond to a model consisting of smooth surfaces within these cavities. Decreasing D , D , D and D values occur when Co atoms are present in the MoS laminates, which promote the formation of smoother edges and denser surfaces that have an influence on the catalytic properties of the S-Mo-S(Co) system.