As environmental regulations increase, more selective transition metal sulfide (TMS) catalytic materials for hydrotreating applications are needed. Highly active TMS catalysts become more and more desirable triggering new interest for unsupported Co-promoted MoS₂-based systems that have high volumetric activity as reported here. Contrary to the common observation for alumina-supported MoS₂-based catalysts, we found in our previous studies with dibenzothiophene (DBT) hydrodesulfurization (HDS) that the catalytic activity is directly proportional to the increase of surface area of the sulfide phases (Co₉S₈ and MoS₂) present in Co-promoted MoS₂ unsupported catalysts. This suggests that activity is directly connected with an increase of the contact surface area between the two sulfide phases. Understanding of the nature of the possible interaction between MoS₂ and Co₉S₈ in unsupported catalytic systems is therefore critical in order to get a more generalized overview of the causes for synergy. This has been achieved herein through the detailed characterization by XRD, XPS, and HRTEM of the highly active Co₉S₈/MoS₂ catalyst resulting in a proposed model for a Co₉S₈/MoS₂ interface. This model was then subjected to a DFT analysis to determine a reasonable description of the surface contact region between the two bulk phases. Modelling of the interface shows the creation of open latent vacancy sites on Mo atoms interacting with Co and formation of direct Co–Mo bonds. Strong electron donation from Co to Mo also occurs through the intermediate sulfur atom bonded to both metals while an enhanced metallic character is also found. These changes in coordination and electronic properties are expected to favor a synergetic effect between Co and Mo at the proposed localized interface region between the two bulk MoS₂ and Co₉S₈ phases.

The chemical synthesis of gold nanoparticles (NP) by using gold (III) chloride trihydrate (HAuCl∙3H₂O) and sodium citrate as a reducing agent in aqueous conditions at 100 °C is presented here. Gold nanoparticles areformed by a galvanic replacement mechanism as described by Lee and Messiel. Morphology of gold-NP was analyzed by way of high-resolution transmission electron microscopy; results indicate a six-fold icosahedral symmetry with an average size distribution of 22 nm. In order to understand the mechanical behaviors, like hardness and elastic moduli, gold-NP were subjected to nanoindentation measurements—obtaining a hardness value of 1.72 GPa and elastic modulus of 100 GPa in a 3–5 nm of displacement at the nanoparticle’s surface.

A simple low-temperature chemical method to produce metastable hexagonal phase molybdenum oxide (h-MoO3) nanorods and their excellent structural characteristics has been demonstrated. In this approach, h-MoO3 samples were prepared by precipitating molybdenum oxide from an ammonium paramolybdate solution by the adding nitric acid. The structure of h-MoO3 nanorods was examined in detail using high-resolution scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). The SEM data reveal that the nanorod h-MoO3 crystals have the shape of straight hexagonal rods with an aspect ratio ∼60. The HR-TEM results confirm the hexagonal structure of the MoO3 nanocrystals. Computations of the observed TEM data along with x-ray diffraction pattern further confirm the stability of the nanostructure of h-MoO3 rods.

Oxygen incorporated molybdenum sulfide (MoS ₂ ) nanoparticles are highly promising materials in hydrodesulfurization catalysis, mechanical, electric, and optical applications.