Effect of Adding Chelating Ligands on the Catalytic Performance of Rh-Promoted MoS2 in the Hydrodesulfurization of Dibenzothiophene

Abstract

Hydrodesulfurization (HDS) is a widely used process currently employed in petroleum refineries to eliminate organosulfur compounds in fuels. The current hydrotreating process struggles to remove organosulfur compounds with a steric hindrance due to the electronic nature of the current catalysts employed. In this work, the effects of adding chelating ligands such as ethylenediaminetetraacetic acid (EDTA), citric acid (CA) and acetic acid (AA) to rhodium (Rh) and active molybdenum (Mo) species for dibenzothiophene (DBT) HDS catalytic activity was evaluated. HDS activities followed the order of RhMo/ɣ-Al2O3 (88%) > RhMo-AA/ɣ-Al2O3 (73%) > RhMo-CA/ɣ-Al2O3 (72%) > RhMo-EDTA/ɣ-Al2O3 (68%). The observed trend was attributed to the different chelating ligands with varying electronic properties, thus influencing the metal–support interaction and the favorable reduction of the Mo species. RhMo/ɣ-Al2O3 offered the highest HDS activity due to its (i) lower metal–support interaction energy, as observed from the RhMo/ɣ-Al2O3 band gap of 3.779 eV and the slight shift toward the lower BE of Mo 3d, (ii) increased Mo-O-Mo species (NMo-O-Mo ~1.975) and (iii) better sulfidation of Rh and MoO in RhMo/ɣ-Al2O3 compared to the chelated catalysts. The obtained data provides that HDS catalytic activity was mainly driven by the structural nature of the RhMo-based catalyst, which influences the formation of more active sites that can enhance the HDS activity.

Perspectives on strategies for improving ultra-deep desulfurization of liquid fuels through hydrotreatment: Catalyst improvement and feedstock pre-treatment

“…For example, replacement of transition metal sulfide active phases with noble metals has been successfully used. (Zhang et al, 2019a;Majodina et al, 2021). Ru and Pt as additives result in enhanced C-S cleavage activity as was demonstrated when they were added to a Rh-P catalyst and tested on 4,6-DMDBT (Kanda et al, 2022).…”

“…Majodina et al (Majodina et al, 2021) recently tested a series of catalysts with and without chelating ligands tested for DBT HDS (RhMo x /Al 2 O 3 , x = EDTA, acetic acid, citric acid) and observed the following:…”

Towards improvement of hydroprocessing catalysts - understanding the role of advanced mineral materials in hydroprocessing catalysts

“…Noble metals (Pd, Pt, Ru, Re, Rh, and Ir) have also been widely investigated for deep HDS catalysis due to their high hydrogenation and hydroisomerization activities, Pd and Pt being the most prominent [36,102,103] . Weise et al compared an unpromoted Pt catalyst with a Pt-doped industrial CoMo catalyst and observed a 46% increase in activity in the latter, attributing the increase in catalytic performance to the incorporation of Pt atoms on the terminal edges and corner sites of CoMo [104] . Pt reduced the binding energy of sulfur, favored the formation of CUS, and created sites that are favorable to the adsorption of sterically hindered molecules such as 4,6-DMDBT [104,105] .…”

“…We recently reported higher HDS of DBT due to a good synergistic effect between Rh promoter and Mo and more MoS 2 /RhMoS phases when we tested a series of RhMo-x/Al 2 O 3 catalysts with different chelating ligand ratios (x = ethylene diamine, tetraacetic acid, acetic acid, citric acid) [104,105] . We attributed high activity to electron donation from Rh to the Mo conducting band, weakening Mo-S bonds and facilitating the formation of CUS [Figure 3].…”

“…Iron has attracted the most attention due to its low cost, high crust abundance, and environmental friendliness [36] . Fe has some level of hydrogenation activity as it is known to have lattice structures and an unfilled d-electron layer, similar to metal species that are used in conventional [104,105] . DBT: Dibenzothiophene; DDS: direct desulfurization; HDS: hydrogenation-desulfurization.…”