Total Scattering Debye Function Analysis: Effective Approach for Structural Studies of Supported MoS₂-Based Hydrotreating Catalysts

Abstract

High dispersion and low degree of crystallinity of supported MoS2 nanoparticles have almost excluded the conventional X-ray diffraction (XRD) analysis from a range of physical methods for the characterization of molybdenum-based hydrotreating catalysts. High-resolution transmission electron microscopy (HRTEM) remains a powerful and preferred technique for obtaining information on the dispersion of supported MoS2 nanoparticles and stacking degree of MoS2 slabs. Here, we report a new approach to study the supported MoS2 nanoparticles in catalysts on the basis of XRD data. Alumina-supported MoS2 catalysts were investigated by means of the Debye function analysis (DFA) applied to the XRD data obtained using the conventional laboratory equipment. Through a direct simulation of XRD profiles by the DFA technique, structural information is extracted from both Bragg and diffuse scattering. We demonstrate that it is possible to determine the average size of coherently scattering MoS2 crystallites, crystallite size distribution, as well as average number of stacked layers in the MoS2 particles from the XRD data. Compared to the widely used HRTEM study, the DFA analysis underestimates the MoS2 particle size due to structural defects. The significant discrepancy between the XRD and HRTEM data serves as an indicator of abundant defects causing a multidomain structure of MoS2 particles. It is shown that HRTEM and XRD data complement each other by providing information on the MoS2 dispersion at different levels of particle organization.

Extension of Rietveld Refinement for Benchtop Powder XRD Analysis of Ultrasmall Supported Nanoparticles

“…The feasibility would also depend on how well the diffractogram of the unknown material could be separated from the support. 53 ). The intensity correction methods presented in this work could similarly be applied before DFA analyses and therefore aid in their background subtractions.…”

Determining the disordered nanostructure of calcium silicate hydrate (C‐S‐H) from broad X‐ray diffractograms

“…It is thus a more general method, compared with Rietveld‐like methods, considering not only the diffraction at the Bragg planes but also the contribution from each atom pair in the entire object. That allows accounting for the diffuse scattering of any set of atoms, including single molecules or non‐periodic materials, in addition to obtaining structural information sensitive to crystalline defects, particle size and shape, symmetry, and surface properties 22–24 …”

“…That allows accounting for the diffuse scattering of any set of atoms, including single molecules or non-periodic materials, in addition to obtaining structural information sensitive to crystalline defects, particle size and shape, symmetry, and surface properties. [22][23][24] To calculate the scattering intensity profile via DFA, all the interatomic distances r ij in the material structure are enumerated via the Debye scattering equation 25,26 :…”

“…28,29 With increased research into the nano-sized matter and further advances in computational power, the interest in the DFA method has resurged. However, despite its potential to predict the nanostructure of layered mineral oxides 30,31 and inorganic two-dimensional (2D) nanomaterials 22,32 being recently demonstrated, its applicability to C-S-H or analogous cementitious phases has not been explored.…”

“…DFA calculations of the built nanostructures were performed using the open-source DIANNA software, 25,26 which has been successfully applied to the analysis of different nanostructured materials. 22,[30][31][32] The calculations considered the C-S-H nanoparticles with a parallelepiped shape. A 2θ range of 5−90 • , step size of 0.1 • , and an Xray wavelength of 1.5406 Å were adopted in the calculations.…”