Effects of the support Brønsted acidity on the hydrodesulfurization and hydrodenitrogention activity of sulfided NiMo/Al 2 O 3 catalysts

Interplay Between Ni and Brønsted and Lewis Acid Sites in the Hydrodesulfurization of Dibenzothiophene

Ni-MoS2/γ-Al2O3 catalysts are commonly used in hydrotreating to enhance fossil fuel quality. The extensive research on these catalysts reveals a gap in understanding the role of Ni, often underestimated as an inactive sulfide phase or just a MoS2 promoter. In this work, we focused on analyzing whether well-dispersed supported nickel nanoparticles can be active in the hydrodesulfurization of dibenzothiophene. We dispersed Ni by Strong Electrostatic Adsorption (SEA) method across four supports with different types of acidity: silica (~ neutral acidity), γ-Al2O3 (Lewis acidity), H+-Y zeolite, and microporous-mesoporous H+-Y zeolite (both with Brønsted-Lewis acidity). Our findings reveal that Ni is indeed active in dibenzothiophene hydrodesulfurization, even with alumina and silica as supports, although their catalytic activity declines abruptly in the first hours. Contrastingly, the acid nature of zeolites imparts sustained stability and performance, attributed to robust metal-support interactions. The efficacy of the SEA method and the added mesoporosity in zeolites further amplify catalytic efficiency. Overall, we demonstrate that Ni nanoparticles may perform as a hydrogenating metal in the same manner as noble metals such as Pt and Pd perform in hydrodesulfurization. We discuss some of the probable reasons for such performance and remark on the role of Ni in hydrotreatment.

Synthesis of Oxygenated Hydrocarbons from Ethanol over Sulfided KCoMo-Based Catalysts: Influence of Novel Fiber- and Powder-Activated Carbon Supports

Ethanol has become a viable feedstock for basic organic synthesis. The catalytic conversion of ethanol provides access to such chemicals as diethyl ether, ethyl acetate, and acetaldehyde. Carbonaceous materials are extensively studied as supports for heterogeneous catalysts due to their chemical and thermal stability, high surface area, and tunable texture. In this paper, ethanol conversion over K10Co3.7Mo12S-catalysts supported on novel activated carbon (AC) materials (i.e., novel powder-AC (DAS and YPK-1), fiber non-woven AC material (AHM), and fabric active sorption (TCA)) was investigated. The catalysts were prepared by the incipient wetness co-impregnation method followed by sulfidation. The catalysts were characterized by employing N2 adsorption–desorption measurements, TEM, SEM/EDX, UV–Vis spectroscopy, and XRF. Catalytic performance was assessed in a fixed-bed down-flow reactor operating at 320 °C, 2.5 MPa, and with continuous ethanol feeding in an He atmosphere. Activity is highly dependent on the support type and catalyst’s textural properties. The activity of the fiber-supported catalysts was found to be greater than the powder-supported catalysts. Ethanol conversion at T = 320 °C, P = 2.5 MPa, and GHSV = 760 L h−1 kgcat−1 increased as follows: (38.7%) KCoMoS2/YPK-1 < (49.5%) KCoMoS2/DAS < (58.2%) KCoMoS2/TCA < (67.1%) KCoMoS2/AHM. Catalysts supported by powder-AC enhanced the formation of MoS2-crystallites, whereas the high acidity of fiber-AC seemed to inhibit the formation of MoS2-crystallites. Simultaneously, a high surface area and a microporous catalytic structure enhance the formation of oxygenates from hydrocarbons. The dehydration and dehydrogenation reactions, which led to the creation of ethene and acetaldehyde, were shown to require a highly acidic catalyst, while the synthesis of ethyl acetate and higher alcohols required a less acidic catalyst.

Monolayer CoMoS Catalysts on Hierarchically Porous Alumina Spheres as Bifunctional Nanomaterials for Hydrodesulfurization and Energy Storage Applications

In this work, CoMoS catalysts were synthesized onto porous alumina spheres obtained using Pluronic P-123 (PS) or urea (US) and used as bifunctional nanomaterials for two energy applications: hydrodesulfurization and energy storage. For the first application, the catalysts were assessed in a hydrodesulfurization reactor using two model sulfur molecules, dibenzothiophene and 4,6-dimethyl dibenzothiophene, as well as feeding a heavy oil fraction. The results indicated that the spheres obtained by Pluronic P-123 allowed a greater dispersion degree of MoS2 slabs than US, indicating that the size and hierarchically porous structure of alumina spheres played a principal role as a booster of the HDS catalytic efficiency of DBT, 4,6 DMDBT and diesel fuel. Then, these catalysts were used for the electrocatalysis of the oxygen reduction and oxygen evolution reactions (ORR/OER), which take place in rechargeable Zn-air batteries. For the ORR, the CoMoS catalyst on PS in the presence of a conductive support (N-doped carbon nanotubes + graphene) displayed an overpotential of only 90 mV in comparison with Pt/C. Importantly, the chalcogenide enabled an increase in the stability, maintaining almost two times higher current retention than Pt/C for the ORR and IrO2/C for the OER. These results suggest that expended chalcogenides from the hydrodesulfurization industry can have a second life as co-catalysts for renewable energy storage systems, enabling a circular economy.

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

Reliance on crude oil remains high while the transition to green and renewable sources of fuel is still slow. Developing and strengthening strategies for reducing sulfur emissions from crude oil is therefore imperative and makes it possible to sustainably meet stringent regulatory sulfur level legislations in end-user liquid fuels (mostly less than 10 ppm). The burden of achieving these ultra-low sulfur levels has been passed to fuel refiners who are battling to achieve ultra-deep desulfurization through conventional hydroprocessing technologies. Removal of refractory sulfur-containing compounds has been cited as the main challenge due to several limitations with the current hydroprocessing catalysts. The inhibitory effects of nitrogen-containing compounds (especially the basic ones) is one of the major concerns. Several advances have been made to develop better strategies for achieving ultra-deep desulfurization and these include: improving hydroprocessing infrastructure, improving hydroprocessing catalysts, having additional steps for removing refractory sulfur-containing compounds and improving the quality of feedstocks. Herein, we provide perspectives that emphasize the importance of further developing hydroprocessing catalysts and pre-treating feedstocks to remove nitrogen-containing compounds prior to hydroprocessing as promising strategies for sustainably achieving ultra-deep hydroprocessing.

Hydrodesulfurization of 4,6-Dimethyldibenzothiophene and the Diesel Oil Fraction on NiMo Catalysts Supported over Proton-Exchanged AlMCM-41 and TiMCM-41 Extrudates

NiMo catalysts supported on mesoporous MCM-41 type materials shaped with binder were tested for activity in the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the diesel fuel fraction (0.92 wt% of sulfur). The aim of the investigation was to evaluate the effect of ion exchange with protons of Al- or Ti-substituted MCM-41 mesoporous supports. The subjected catalytic systems were NiMo/HAlMCM-41 and NiMo/HTiMCM-41, and for comparison purposes NiMo/AlMCM-41 and NiMo/TiMCM-41. The samples were characterized by N2 sorption (at 77 K), XRD, TEM, XPS, SEM and Py–IR. It was found that the functionalization of AlMCM-41 and TiMCM-41 with protons increased the conversion of 4,6-DMDBT and the pseudo-first-order rate constant. Correspondingly, 4,6-DMDBT HDS reactions over the NiMo/HTiMCM-41 catalyst proceeded to a similar extent via hydrogenation and direct desulfurization, whereas over the NiMo/HAlMCM-41 they proceeded mainly via direct desulfurization. Furthermore, the ion-exchanged catalysts displayed two-fold higher efficiency in direct desulfurization than their non-modified counterparts. The NiMo/HTiMCM-41 catalyst exhibited the highest catalytic efficiency in the HDS of 4,6-DMDBT and the diesel oil fraction. The high activity of the NiMo/HTiMCM-41 catalyst is mainly attributed to its appropriate acidity, as well as the metal–support interaction providing both the high dispersion of the active phase and the desirable multilayered stacking morphology of the active phase slabs.

Design and Evaluation of a Co-Mo-Supported Nano Alumina Ultradeep Hydrodesulfurization Catalyst for Production of Environmentally Friendly Diesel Fuel in a Trickle Bed Reactor

In the present work, a nanocatalyst, γ-Al₂O₃ nanoparticle-supported CoMo, was prepared experimentally and evaluated through a hydrodesulfurization (HDS) process for removing dibenzothiophene (DBT) from diesel fuel systematically in a trickle bed reactor (TBR). The results of the prepared catalyst characterization tests (scanning electron microscopy, X-ray diffraction (XRD), XRD phase quantification, and Brunner-Emmett-Teller) showed good distribution of active metals (CoMo), difference in surface morphology, and high dispersion of active metals. The catalyst exhibited good metal-support interactions without impacting the surface area significantly. A fully automated TBR reactor was used to evaluate the activity of the prepared catalyst in the HDS process at ranges of operating conditions: temperatures (250-350 °C), pressures (6-10 bar), liquid hourly space velocities (LHSV) (1-3 h^-1), and the activity of the prepared catalyst were compared to a commercial catalyst based on Co-Mo/γ-alumina. The results showed an obvious enhancement in the HDS process using the homemade nanocatalyst compared to the commercial catalyst. It has also been found that an increase in temperature led to an increase in the conversion from 68.77 to 91.57%, a little positive effect on conversion when pressure was increased, and a significant decrease in conversion (from 91.57 to 75.58%) as LHSV was increased. A kinetic model was developed for the HDS process to estimate kinetic parameters and apply the parameters in reactor design. The developed model showed that the DBT concentration in diesel fuel can be reduced significantly, 3000-240 ppm, at the optimum experimental conditions.

Transition Metal Sulfides- and Noble Metal-Based Catalysts for N-Hexadecane Hydroisomerization: A Study of Poisons Tolerance

Bifunctional catalysts on the base of transition metal sulfides (CoMoS and NiWS) and platinum as noble metal were synthesized via wetness impregnation of freshly synthesized Al2O3-SAPO-11 composites, supported with favorable acidic properties. The physical-chemical properties of the prepared materials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), low-temperature N2 adsorption and high resolution transmission electron microscopy (HR TEM) methods. Catalytic properties were studied in n-hexadecane isomerization using a fixed-bed flow reactor. The catalytic poisons tolerance of transition metal sulfides (TMS)- and Pt-catalysts has been studied for sulfur and nitrogen, with the amount of 10–100 ppm addition to feedstock. TMS-catalysts show good stability during sulfur-containing feedstock processing, whereas Pt-catalyst loses much of its isomerization activity. Nitrogen-containing compounds in the feedstock has a significant impact on the catalytic activity of both TMS and Pt-based catalysts.

Simultaneous Adsorption of 4,6-Dimethyldibenzothiophene and Quinoline over Nickel and Boron Modified Gamma-Al2O3 Adsorbent

The simultaneous adsorption of quinoline and 4,6-dimethyldibenzothiophene over adsorbents, based on alumina modified with boron and nickel under ambient temperature and pressure, was studied. The adsorbents were characterized by BET specific surface area, a potentiometric method for the determination of acid strength, electrophoretic migration, and X-ray diffraction. The results showed that the adsorbent containing nickel had better adsorption capacity than the adsorbent modified with nickel and boron, which was attributed to its greater acidity and ability to generate π-complexation between the adsorbent and the molecules. In terms of selectivity, quinoline was more adsorbed than 4,6-dimethyldibenzothiophene in all systems, due to the basic nature of quinoline. The experimental data in all cases were adjusted by three kinetic models (Yoon–Nelson, Yan and Thomas), and the regression coefficients in all models were close to one. Finally, the values of the kinetic constant obtained by the Thomas model were used to relate the adsorption capacity results.

Promoting effects of SO42− on a NiMo/γ-Al2O3 hydrodesulfurization catalyst

SO₄²⁻ anchors to a NiMo/γ-Al₂O₃ catalyst, weakening the metal–support interactions, inhibiting MoS₂ aggregation, increasing the number of Ni–Mo–S sites, and thus improving its activity and stability.

Recent Insights in Transition Metal Sulfide Hydrodesulfurization Catalysts for the Production of Ultra Low Sulfur Diesel: A Short Review

The literature from the past few years dealing with hydrodesulfurization catalysts to deeply remove the sulfur-containing compounds in fuels is reviewed in this communication. We focus on the typical transition metal sulfides (TMS) Ni/Co-promoted Mo, W-based bi- and tri-metallic catalysts for selective removal of sulfur from typical refractory compounds. This review is separated into three very specific topics of the catalysts to produce ultra-low sulfur diesel. The first issue is the supported catalysts; the second, the self-supported or unsupported catalysts and finally, a brief discussion about the theoretical studies. We also inspect some details about the effect of support, the use of organic and inorganic additives and aspects related to the preparation of unsupported catalysts. We discuss some hot topics and details of the unsupported catalyst preparation that could influence the sulfur removal capacity of specific systems. Parameters such as surface acidity, dispersion, morphological changes of the active phases, and the promotion effect are the common factors discussed in the vast majority of present-day research. We conclude from this review that hydrodesulfurization performance of TMS catalysts supported or unsupported may be improved by using new methodologies, both experimental and theoretical, to fulfill the societal needs of ultra-low sulfur fuels, which more stringent future regulations will require.

Ultrasound-assisted oil removal of γ-Al2O3-based spent hydrodesulfurization catalyst and microwave roasting recovery of metal Mo

Currently, roasting-leaching is the main treatment process of spent hydrodesulfurization (HDS) catalyst, but it will produce impurities, such as nickel molybdate and cobalt molybdate (NiMoO₄ or CoMoO₄), which is adverse to recover valuable metals. In this paper, a combined ultrasonic-microwave method was developed to remove oil and recover molybdenum (Mo) from the spent HDS catalyst. Firstly, ethanol was used to extract the surface oil of the spent MoNiCo/Al₂O₃ catalyst with ultrasonic assistance. Effects of temperature, ultrasonic time, liquid-solid ratio and ultrasonic power on the oil removal rate were investigated systematically and the process conditions were optimized using response surface methodology (RSM). The results showed that the oil removal rate was over 99% under the optimum conditions of temperature 55 °C, ultrasonic time 2 h, liquid to solid ratio 5:1, and ultrasonic power 600 W. After oil removal, the sample was roasted in microwave field at 500 °C for 15 min. The generation of toxic gas could be effectively avoided and no hardest-to-recycle impurity CoMoO₄ was found. At last, the roasted sample was subjected to ultrasonic leaching with sodium carbonate (Na₂CO₃) solution for recovering Mo. Extraction of Mo of the deoiled sample after microwave roasting reached 94.3%, which is about 7% higher than that of oily sample. Moreover, microwave roasting method resulted in a much higher Mo extraction than traditional method for both the oily and deoiled spent catalyst. It was concluded that the ultrasonic-microwave assisted method could remarkably improve the recovery of Mo and greatly shorten the processing time.