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

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.