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Palladium nanoparticles with defined morphologies were synthesized using a seed-mediated approach in the presence of cetyltrimethylammonium bromide (CTAB). This seeding technique, already applied to Ag and Au nanostructures, was successfully extended here to Pd, a noble metal with important applications in catalysis. Various types of morphologies were obtained going from 0-D nanocrystals (cubes, icosahedral multiply twinned particles) to 1-D (nanorods) and 2-D nanocrystals (triangular nanosheets). Palladium nanorods were obtained in a relatively high yield and present a well-defined 5-fold symmetry similar to that reported previously for Ag and Au. Embedding the PdCl 4 2precursor inside CTAB micelles was found to be a key parameter to decrease the rate of reduction of palladium and to allow a better kinetic-controlled growth regime, favoring the formation of nanorods. Shifting the experimental conditions to a thermodynamic-controlled growth regime also selectively led to the formation of cubic (∼80%) or icosahedral (∼100%) particles.

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 MoS 2 -based systems that have high volumetric activity as reported here. Contrary to the common observation for alumina-supported MoS 2 -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 (Co 9 S 8 and MoS 2 ) present in Co-promoted MoS 2 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 MoS 2 and Co 9 S 8 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 Co 9 S 8 / MoS 2 catalyst resulting in a proposed model for a Co 9 S 8 /MoS 2 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 MoS 2 and Co 9 S 8 phases.

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