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Carbon nanohorns (CNH), other carbon particles (OCP), fine fractions of other carbon particles (OCPf), carbon nanotubes (CNT), and γ-alumina (γ-Al2O3) were utilized as support materials for the Ni–Mo catalyst in this study to test the influence of the support on hydrotreating efficiency using light gas oil (LGO) and identify the cause of disparity in activity from these various catalyst supports. OCP and OCPf are the main byproducts obtained during the production of CNH. The influence of the support on the hydrotreating catalyst is significant and includes enhancement of textural properties, active phase dispersion, and catalyst reducibility. The hydrodenitrogenation activities of all of the different supported catalysts with light gas oil are presented and correlated with their physicochemical properties. Among all of the carbon-supported catalysts used, the NiMo/CNH catalyst exhibited outstanding physicochemical properties, and as such, its hydrodesulfurization activity of 89% dominated that of NiMo/OCPf (78%), NiMo/OCP (67%), and NiMo/CNT (73%) catalysts. The pore volume, pore diameter, and surface area of the NiMo/CNH catalyst was 0.42 cm3/g, 10.9 nm, and 350 m2/g, respectively. The percentage metal dispersion of the NiMo/CNH catalyst was 8.0% and was about twice that of the NiMo/OCPf and NiMo/CNT catalysts. X-ray absorption spectroscopy (XAS) analysis confirmed that the carbon-supported catalysts exhibited a distorted octahedral Mo coordination environment, whereas the NiMo/γ-Al2O3 catalyst exhibited a mixture of octahedral and tetrahedral Mo environment. From XAS results, it was apparent that the possession of a Mo octahedral coordination environment does not always translate to attainment of highest hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities.

The submerged arc in liquid nitrogen method was used to produce carbon nanohorns (CNH) for hydrotreating application. In this paper the effects of current, time and system design modification were investigated to maximize CNH production. A current setting of 90 A was found to be the best condition for CNH production. Additionally, CNH production was impacted by processing time and design setup used in synthesizing the samples. For each batch, 0.12 g of CNH was obtained for 30 mins of processing time. The properties of CNH were evaluated using Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Raman Spectroscopy and X-ray diffraction (XRD). BET results revealed mesoporous pore diameters for all pristine CNH samples under the different current (50–100 A) settings. Dahlia-like and budlike structures with aggregate diameters ranging from ~50–110 nm were observed in the TEM images. Although current and processing times were found to be two crucial parameters affecting the yield of CNH production, the entire equipment design was a major key factor in improving the yield by being capable of retaining more CNH particles during production.

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The by-products collected during the synthesis of carbon nanohorns via the arc discharge synthesis method is comprised of other carbon particles (OCP). At a hydrotreating operating temperature of 370°C, preliminary investigations using a bimetallic catalyst with support originating from the fine fractions of other carbon particles (OCPf) and containing 13 wt% Mo and 2.5 wt% Ni resulted in an HDS and HDN conversion of 78 and 25%, respectively. Variation of metal compositions in catalyst formulation and its impact on hydrotreating activity was therefore considered in this study to enhance the hydrotreating activity of OCPf–supported catalyst, and to determine if the best NiMo/OCPf catalyst achieved from this study could be a viable catalyst for hydrotreating applications. The co-incipient wetness impregnation was used in preparing series of hydrotreating catalysts with Ni and Mo loadings within the range of (2.5–5.0 wt%) and (13–26 wt%) respectively. Overall, the catalyst samples with maximum Ni loading of 5.0 wt% and Mo loadings of either 13 or 19 wt% showed higher dispersion and the ability to form a Type II Ni-Mo-S phase with enhanced activity. The effects of metal compositions on both HDS and HDN activities were correlated with their physicochemical properties.