Generation of Model NiMo Hydrotreating Nano-catalyst via the Spark Discharge Technique

Abstract: Establishing a technically practical method to generate representative model catalysts for the use in characterizations and testing prior to catalyst implementation in chemical process units would allow for a more sophisticated understanding of the underlying catalytic mechanisms. As a step towards establishing such a method, generating non-agglomerated, spherical NiMo nanoparticles, with diameters below 25 nm and atomic composition of maximum 30 at% Ni with Mo (maximum 3:7 Ni:Mo atomic ratio), for application as model hydrotreating catalysts, was addressed. The investigated method for the generation of these model nano-catalysts was the Spark discharge technique. The generation of nanoparticles through this method is carried out by employing an electric circuit, across which electrodes are connected and evaporate upon the application of a sufficiently high voltage. A furnace and a deposition chamber were also incorporated post the Spark discharge chamber to improve the morphological properties of the generated nanoparticles via sintering, and to yield supported nanoparticles for further characterizations of the nano-catalysts through SEM, EDXS and XAS. Combinations of different system parameters were tested to deduce how the morphological and compositional characteristics of the nanoparticles are affected by these, including parameters in the electric circuit and furnace temperature. Nanoparticles with variable characteristics were followingly yielded upon employing the different parameter combinations. Among these, nonagglomerated, spherical nano-catalysts with an average diameter of about 19.6 nm were generated as desired. The obtained compositions were 3:7 and 1:4 Ni:Mo atomic ratio. Finally, the parameter combination that produced nanoparticles with the desired properties was determined and discussed in detail. Additionally, as a means of assessing the suitability of the generated nanoparticles as nano-catalyst, the reducibility of the Ni and Mo in the nanocatalysts was examined and compared to that of industrial references.