Abstract
A study was made by a combination of 3D electron tomography reconstruction methods and N2 adsorption for determining the fractal dimension for nanometric MoS2 and MoS2/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 MoS2 and MoS2/Co particles. Neimark-Kiselev’s equations afforded the evaluation of a pore volume variation from 10 to 110 cm3/g by cobalt insertion in the MoS2 crystallographic lattice, which induces the formation of cavities and throats in between of less than 29 nm, with a curvature radius rk < 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 DP, DB, DI and DM values occur when Co atoms are present in the MoS2 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.
Highlights
Catalytic materials are the main pillars of liquid fuels production from hydrocarbons and its role is vital for supplying energy needs from petroleum natural resources
Surface fractal dimensionality is related to the roughness, steps and kinks at the molecular scale and it plays a key role for heterogeneous catalysts, as pointed out by several authors[27,28,29,30]. We propose this parameter as an important one for gauging catalytic behavior of Co-promoted-MoS2 catalysts and as a complement of “electronic effects” induced by insertion of the Co promoter, because it modifies both textural and structural properties of MoS2; this is the first time that fractal dimensionality is shown as a result of Co-promoter insertion in spherical particles of MoS2 and the profound effects on both texture and structure as verified in the case of MoS2/ Co system
The crystallographic features of hydrothermally as-synthesized Cobalt promoted MoS2 catalysts were determined by X-ray powder diffraction (Table 1); this comprised the use of Rietveld’s refinement method to verify the MoS2 rhombohedral (R3m) symmetry, in agreement with recent work from Wang et al.[31], from which a comparative analysis was performed as shown by Fig. 1, where one observes that a crystallographic variation occurs following cobalt addition during synthesis (Table 2), which can be explained in terms of Frenkels point defects[32] (Table 3) caused by interstitial occluded cobalt atoms into the laminar MoS2 structure, as described by Lauritsen et al.[14]
Summary
Catalytic materials are the main pillars of liquid fuels production from hydrocarbons and its role is vital for supplying energy needs from petroleum natural resources. Surface fractal dimensionality is related to the roughness, steps and kinks at the molecular scale and it plays a key role for heterogeneous catalysts, as pointed out by several authors[27,28,29,30] We propose this parameter as an important one for gauging catalytic behavior of Co-promoted-MoS2 catalysts and as a complement of “electronic effects” induced by insertion of the Co promoter, because it modifies both textural and structural properties of MoS2; this is the first time that fractal dimensionality is shown as a result of Co-promoter insertion in spherical particles of MoS2 and the profound effects on both texture and structure as verified in the case of MoS2/ Co system
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
