Hydrodesulfurization Reaction Research Articles

Effect of Gallium as an Additive Over Corresponding Ni-Mo/γ-Al2O3 Catalysts on the Hydrodesulfurization Performance of 4,6-DMDBT.

Experiments were carried out to research the different contents of Ga2O3 modification effects on the hydrodesulfurization (HDS) performance of 4,6-dimethyldibenzothiophene (4,6-DMDBT) catalyzed by the stepwise impregnation method. Characterization techniques such as XRD, BET, HRTEM, NH3-TPD, and Py-FTIR were performed to determine the effects of each modification of the catalyst by Ga on the properties of the prepared supports and catalysts. The catalytic effect of gallium is reflected in the fact that the empty d-orbitals of Ga elements participate in the formation of molecular orbitals in the active center and change their orbital properties, thus generating a direct desulfurization active phase suitable for complex sulfides for endpoint adsorption. The characterization results indicated that the introduction of Ga2O3 with appropriate content (2 wt.%) promoted Ni and Mo species to disperse uniformly and doping of more Ni atoms into the MoS2 crystals, which also increased the average stacking number and the length of MoS2. As a result, more NiMoS active phases were favored to form in the system. The specific surface area and the amounts of acid sites were increased, facilitating the adsorption of reactant molecules and the HDS reactions. The HDS results also suggested the effects of Ga modification play a very important role in the catalytic performance of the corresponding catalysts. The catalyst Ga–Ni–Mo/Al2O3 exhibited the highest conversion rate towards 4,6-DMDBT HDS when the amount of Ga2O3 loading was 2 wt.% with an LHSV of 2.5 h−1 at 290°C and Ga modification also can effectively improve the direct desulfurization (DDS) route selectivity in varying degrees.

Role of Phosphorus and Triethylene Glycol Incorporation on the Activity of Model Alumina‐Supported CoMoS Hydrotreating Catalysts

AbstractEnvironmental regulations concerning fuel‐related sulfur emissions are currently experiencing worldwide expansion. This is motivating the research and development of improved hydrotreating (HDT) catalysts with carefully engineered synthesis methods that maximize activity as ultimate goal. In this contribution, the effect of phosphorus doping and triethylene glycol (TEG) incorporation on the genesis of the CoMoS phase of model HDT catalysts is assessed. Following a surface‐science approach, α‐Al2O3 single crystals with four orientations: C(0001), A(11 0), M(10 0), and R(1 02) are used as model supports of the traditional γ‐Al2O3 support for the study of active phase‐support interactions at the molecular scale. The model catalysts are prepared by traditional impregnation of a solution containing metal and phosphorus precursors and TEG. The catalysts are characterized in the sulfide phase by XPS, XAS, TEM, and AFM, revealing that the calcination step is key in the emergence of distinctive metal‐support interactions, which are directly related to the nature of alumina surface sorption sites. In addition, TEG incorporation on dried catalysts increases metal sulfidation and enhances promotion with respect to non‐additivated systems, especially at mild sulfidation temperatures. The catalytic activity of the model catalysts is tested in a thiophene hydrodesulfurization reaction, revealing the following activity trend with respect to alumina surface orientations: A ≫ M >R , C(0001). This trend is identical to the one observed for non‐phosphorus doped non‐TEG additivated model systems, confirming the predominance of surface effects on the catalytic activity over those exerted by P and TEG. By transposing these results to the industrial γ‐Al2O3 support, the (100) facet would provide surface sites that lead to better performing catalysts. This could result in the development of novel supports, engineered to expose surface sites that maximize hydrotreating activity.

Mesoporous Gamma‐Alumina‐Supported Mo Catalysts: Effect of Calcination Temperature

AbstractMesoporous γ‐Al2O3‐supported Mo oxides precursors were prepared by one‐step hydrolysis method without organic template at different calcination temperatures (MoOx/γ‐MA‐T) from 400 to 700 °C. Then MoS2 catalysts (MoS2/γ‐MA‐T) were obtained from the precursors through in‐situ sulfurization and applied for hydrodesulfurization (HDS) of dibenzothiophene (DBT). Effects of precursors calcination temperature on physicochemical properties and catalytic performances of catalysts were systematically investigated. With the increase of calcination temperature, the strength of metal‐support interactions and slab lengths of MoS2 increased. The slab stacks were inhibited by the strengthened strong interaction, leading to the reduction of edge/rim sites ratio that are favour for the HDS reaction. Appropriate calcination temperature (500 °C) could make the MoS2/γ‐MA‐500 possess favourable pore structure, particle dispersion, and edge/rim sites ratio, which were conducive to the mass transfer process of reactants and products, and lowered the carbon deposition rate, thus improving its catalytic activity, stability and direct hydrogenolysis desulfurization selectivity.

The effect of chelating agent on hydrodesulfurization reaction of ordered mesoporous alumina supported NiMo catalysts

In this paper, ordered mesoporous alumina (OMA) support with the high surface area (328 m 2 g −1 ) and the large pore volume 0.74 (cm 3 ·g −1 ) was synthesized by homogeneous precipitation method. And the influence of EDTA on the physical and chemical properties of the modified catalysts was also studied. The characteristic results showed that the addition of EDTA could adjust the metal-support interaction and improved the acidity of the corresponding catalyst. Combined with the catalytic performance results, the EDTA-modified NiMoE(1.0)/OMA catalyst displays the highest DBT hydrodesulfurization conversion (97.7%).

Infrared Spectroscopic Evidence of WS2 Morphology Change With Citric Acid Addition and Sulfidation Temperature

MS2 morphology is strongly influenced by several parameters including the addition of a chelating agent and sulfidation temperature. In this work, we report the use of citric acid as chelating agent in order to prepare a series of WS2/Al2O3 catalysts that were submitted to sulfidation at several temperatures. The effect of these two parameters in the morphology of the slabs was explored by means of CO adsorption at low temperature followed by IR spectroscopy (IR/CO) and later confirmed by High-Resolution Scanning Transmission Electron Microscopy coupled with High Angular Annular Dark Field detector (HR STEM - HAADF). This allowed to depict the morphology of WS2 slabs by means of calculating the M-edge/S-edge site ratio. The use of citric acid in the preparation stage favors the increase of S-edge site concentration whereas it keeps that of M-edge sites: according to IR/CO, with an increasing amount of citric acid, the WS2 morphology progressively changes from a slightly truncated triangle exhibiting predominantly M edges to a hexagon with both M edge and S edge. In addition, HR STEM-HAADF demonstrated that the addition of citric acid in the impregnation step of W catalysts considerably reduces the size of WS2 nanoparticles increasing their dispersion degree. The morphology of the WS2 plates on the activated WS2/Al2O3 catalyst with a typical sulfidation temperature range (573–673 K) was detected to be a truncated triangle exposing both the M-edge and the S-edge. Furthermore, the IR/CO results indicate that the degree of truncation (ratio of S-edge/M-edge) of WS2 slabs gradually rises with the increasing sulfidation temperature. However, the most determining factor for a modification of the morphology of the slabs turns out to be the presence of citric acid as a chelating agent and not the sulfidation temperature. This change in morphology (i.e., change of S-edge/M-edge ratio) is a key factor for catalytic performance, since the M-edge and the S-edge show different reactivity in hydrodesulfurization (HDS) reactions. Notably, it was also found that the addition of citric acid not only improves the catalytic activity but also the stability of the catalysts, giving the best performance in concentrations higher than (CA/W = 1).

CoMo/Al2O3-MgO Supported Catalysts: Improvement of Hydrodesulfurization Activity and Optimization of Operational Processing

Hydrodesulfurization (HDS) plays a vital role in the production of clean fuels when more stringent environmental legislation forces the sulfur content in fuels to an ultra-low level. There are two alternative approaches for producing ultra-low sulfur diesel (ULSD) in a cost-effective way, including the activity improvement of HDS catalysts and the optimization of the operating conditions in HDS reactions. In this study, the activity improvement of HDS catalysts was first examined, and then the optimization of operational conditions was further explored to gain the ULSD in a cost-effective way. In detail, the catalysts were improved through optimizing the ratio between active metal (Mo) and promoter (Co) based on the MgO-Al2O3 as support. Precursors of the improved oxide catalysts and sulfide catalysts were characterized by various techniques, and the catalytic performances were further evaluated in the hydrodesulfurization of dibenzothiophene. Catalysts with the best catalytic performance were chosen to optimize the reaction conditions. Results show that the optimal amounts of catalysts were 4 wt.% of MoO3 and combined with 2 wt.% of CoO. Moreover, the optimal reaction conditions were reaction temperature of 240 °C, total reaction pressure of 4.0 MPa, the hydrogen-to-oil volume ratio of 300, and LHSV of 2.0 h−1. Under the optimal reaction condition, the desulfurization rate could reach to 99.8%.

Effects of Al Introduction Methods for Al-Sba-15 on Nimos Active Phase Morphology and Hydrodesulfurization Reaction Selectivities

Effects of Al Introduction Methods for Al-Sba-15 on Nimos Active Phase Morphology and Hydrodesulfurization Reaction Selectivities

One Pot Synthesis of Ultrasmall Nimo Catalysts Supported on Amorphous Alumina with Enhanced Type 2 Sites for Hydrodesulfurization Reaction: A Combined Experimental and Theoretical Study

One Pot Synthesis of Ultrasmall Nimo Catalysts Supported on Amorphous Alumina with Enhanced Type 2 Sites for Hydrodesulfurization Reaction: A Combined Experimental and Theoretical Study

A combined experimental and DFT study on the catalysis performance of a Co-doped MoS2 monolayer for hydrodesulfurization reaction

The effects of Co-doped monolayer MoS2 on the thiophene hydrodesulfurization process were studied via experiments and DFT.

Bimetallic CoMo Nanoparticles Supported over Carbon-Zeolite Composites as Dibenzothiophene Hydrodesulfurization Catalyst

Cobalt molybdenum catalysts supported on novel activated carbon-HZSM-5 composites with different mass ratios were prepared by wet-impregnation method and pre-sulfided by CS2. Characterization of these catalysts was done using X-ray powder diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption, and scanning electron microscope analytics. Their activity for the hydrodesulfurization reaction of dibenzothiophene was investigated at atmospheric pressure in the temperature range of 250–400 °C using the fixed-bed reactor with 0.5 g of each powder and pre-sulfided with CS2. The highest conversion of dibenzothiophene at the temperature range of 300–400 °C was obtained for the CoMo/activated carbon-HZSM-5(1:1) catalyst. The best selectivity for cyclohexylbenzene, which is the dominant product according to gas chromatography results, was obtained at all temperatures using CoMo/activated carbon-HZSM-5(3:1) catalyst. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Experimental proof of thiophene hydrodesulfurization reaction steps by isotope (14C) labeled thiophene

Hydrodesulfurization of thiophene has been studied over alumina supported sulfided molybdena, nickel-promoted molybdena and over nickel (Mo, NiMo and Ni) catalysts. The experiments were carried out with a mixture of thiophene, labeled with radioactive carbon (thiophene-[G-]-14C) and of non-radioactive tetrahydrothiophene (1:1 mol ratio) in a micro catalytic system. It was established, that the main products were tetrahydrothiophene-14C, 1-butene-14C, 2-butene-14C, butane-14C. Tetrahydrothiophene-14C was a major intermediate in the conversion of thiophene—14C in the experimental condition applied. The amounts of converted tetrahydrothiophene on the catalysts were substantially higher than those of thiophene under the same conditions. Hydrothiophene and dihydrothiophene—14C were intermediate products in the hydrodesulfurization of thiophene and tetrahydrothiophene. The hydrodesulphurization of tetrahydrothiophene was paired with dehydrogenation, producing small amounts of thiophene. The experimental results have been considered in the discussion of the mechanism of thiophene and tetrahydrothiophene desulfurization reaction pathway.

Migration and Rearrangement of Fe–Zn Species in the Preparation of Fe–Zn Bimetallic Catalysts and Their Effects on the Hydrodesulfurization Reactivity

Bimetallic chemistry and structural arrangements are effective ways to improve catalytic activity. The Fe–Zn bimetallic catalysts were prepared by urea addition, and their effects on the hydrodesulfurization (HDS) reactivity of dibenzothiophene were investigated. It indicated that the addition of urea changed the bimetallic distribution, resulting in a significant increase in the Fe/Zn atomic ratio on the catalyst surface, which not only promoted the electron donating ability of Zn to Fe but also weakened the interaction between the metal and support. As a result, the sulfidation degree and the FeZnS active phase content in the urea-modified catalyst increased through bimetallic migration and rearrangement during the activation process. This resulted in an enhanced HDS activity by up to 50%, and the rate constant kHDS increased by 3.15 times versus the urea-free catalyst at 613 K. Moreover, it shows that the urea-modified Fe–Zn bimetallic catalysts enhanced the hydrogenation pathway significantly.

Stability and catalytic properties of 1T-MoS2 obtained via solvothermal synthesis

Nanodispersed MoS2 and CoMoS2 materials containing metastable 1T MoS2 phase have been prepared by solvothermal technique, characterized with several physico-chemical methods and evaluated in the electrocatalytic hydrogen evolution (HER), thiophene hydrodesulfurization (HDS) and 1-pentene hydrogenation (HYD) reactions. The role of different factors in the stabilization of 1T MoS2 phase has been studied. Stability of 1T polymorph upon heating was followed by XPS and Raman spectroscopies and evolution of HER activity. The results of characterizations (Raman, XPS, TEM, XRD) converge to the conclusion that ethylene glycol intercalated between the MoS2 layers stabilizes 1T –MoS2 polymorph. When heated above 200 °C, the solids lose the intercalated ethylene glycol molecules and are transformed to 2 H –MoS2. The presence of cobalt does not influence the stability of 1T phase, but improves both HER and HDS performance due to formation of CoMoS species.

Facile synthesis of few-layer MoS2 nanosheets with different morphologies supported on Al-TUD-1 for efficient hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Low-cost pure aluminum-based Al-TUD-1 mesoporous materials (AT) were successfully synthesized and the corresponding NiMo/AT catalysts were modified with Citric acid (CA), which were utilized for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) reactions. CA could effectively modulate the acidity and metal-support-interaction (MSI) of NiMoCA(x)/AT catalysts, which were in favor of generating more MoS2 active species with higher sulfurization degree and higher dispersion degree. The morphology of the MoS2 active phase of NiMoCA(x)/AT catalysts was changed after the addition of CA. The NiMoCA(2)/AT catalyst showed the higher B/L ratio and higher S-edge/M-edge ratio, which was conducive to the isomerization (ISO) route selectivity (81%) of 4,6-DMDBT HDS, thus resulting the improvement of HDS activity of the NiMoCA(2)/AT catalyst. The NiMoCA(2)/AT exhibited the maximal DBT and 4,6-DMDBT HDS efficiency of 99.0% and 95.5% as well as maximal kHDS and TOF values of 4,6-DMDBT HDS (13.4 × 10−4 mol⋅g−1⋅h−1, 4.7 h−1) among other series NiMoCA(x)/AT catalysts and reference commercial NiMo/Al2O3 catalyst at the Weight hour space velocity (WHSV) of 10 h−1.

Rhenium modification on NiMo/Al2O3 catalyst and effects on the hydrodesulfurization reaction route selectivity of 4,6-dimethyldibenzothiophene

A series of Re modified NiMo/Al2O3 hydrodesulfurization (HDS) catalysts with different contents of Re2O7 were successfully synthesized by stepwise impregnation method and co-impregnation method respectively. The effects of Re modification and impregnation methods on the physical-chemical properties of the prepared catalysts were determined by the characterization techniques such as XRD, N2 physical adsorption-desorption, NH3-TPD, Py-FTIR and HRTEM. Finally, the effects of the Re modification and the impregnation methods on the catalytic activity and the HDS reaction route selectivity were evaluated using 4,6-dimethyldibenzothiophene (4,6-DMDBT) as a probe. The results show that the crystal morphologies and pore structures of the synthesized catalysts varied with the contents of Re2O7 and the impregnation methods and the amounts of acid sites can be modulated by the incorporation of Re2O7 and the impregnation methods. Moreover, Re modification was conducive to the formation of the “type II” Ni-Mo-S active phase by changing the morphology of the Ni promoted MoS2 slabs. The HDS evaluation of 4,6-DMDBT results show that Re modification can effectively improve the 4,6-DMDBT conversions, DDS route selectivity and even 3,3′-dimethylcyclohexanebenzene (3,3′-DMCHB) selectivity in varying degrees, and compared with that of co-impregnation method, the Re modification by stepwise impregnation method exhibited a more prominent effect. In general, 1 wt% Re2O7 content was the most favorable to the HDS reaction since excessive Re2O7 content has very little promoting effect.

Control of metal-support interaction in magnetic MoS2 catalyst to enhance hydrodesulfurization performance

Studies on the metal-support interaction have been a key step for deeply understanding the catalytic behavior of hydrodesulfurization (HDS) reactions. In particular, modification of the surface hydroxyl groups on alumina can determine its surface metal species and their dispersion degrees and thus influence the reactivity of catalysts. Herein, magnetic MoS2 nanoparticles supported on thiol groups grafted alumina (Fe3O4@Al2O3-SH@MoS2) were synthesized, leading to excellent catalytic hydrodesulfurization performance in a slurry-phase reactor of 40% desulfurization efficiency and high stability of 105 h in the long-term evaluation. Density functional theory calculations and multiple catalyst characterizations demonstrated that the grafting of thiol groups not only significantly weakened the metal-support interaction by bridging the support and active phase but also inhibited the coke formation, improved the cycle performance of the catalyst. This work proves to be an effective method to adjust the metal-support interaction, leading to enhanced catalytic performance. Besides, the magnetic properties of the catalyst enable it to be separated from the reaction media quickly, which is promising to be used in slurry reactors that process heavy crude oil.

The effect of mass transfer resistance on the kinetics of catalytic hydrodesulfurization of thiophene over Pt/Al2O3

In kinetic study of reactions carried out in the presence of heterogeneous catalyst, it is very important to study the effects of mass transfer rate firstly which can be effective in adding to chemical kinetic. The present work investigates the catalytic hydrodesulfurization (HDS) of thiophene over Pt/ Al2O3, to determine the effect of interface mass transfer resistance. The experimental work was performed in a HDS continuous flow fixed bed catalytic reactor unit consisted of a carbon steel tube (2.54 cm diameter, and 60 cm length), located in the laboratories of chemical engineering department, Baghdad University. The objective of the work was to investigate effect of mass transfer limitations (internal diffusion and external diffusion) in catalytic reaction of thiophene HDS. It was verified that mass transfer resistances has a small effect on the reaction rate.

Combined DFT and microkinetic modeling study of [formula omitted] hydrodesulfurization reaction on [formula omitted] catalyst

Optimizing catalysts for the SO2 hydrodesulfurization (HDS) is a crucial step toward conforming with the environmental requirements concerning SO2 emissions. Nickel phosphides have been reported as efficient catalysts in HDS reaction. However, how HDS reaction proceeds on nickel phosphides is not well understood. On this context, the present work focuses on the mechanistic understanding of SO2 HDS reaction over Ni5P4surfaces. The adsorption of both reactants, SO2 and H2 molecules, on low-index facets of Ni5P4 crystal, namely (001), (011), (111), (110) , (101), (010) and (100) surfaces, were investigated using density functional theory (DFT) calculations. The stability of Ni5P4 surfaces was examined and (001) surface was found to be the most stable surface. Therefore, microkinetic modeling was conducted on Ni5P4(001) surface to predict the catalytic preferred pathways. Reaction towards H2S, main product, exhibited 100% selectivity at reaction temperatures below 700 K, however the selectivity towards H2O became dominant at higher temperatures. This is because the barrier for HS- hydrogenation to H2S (1.20 eV) is lower than that of the OH hydrogenation to H2O (2.37 eV). The model revealed that conversion of HS- ions to H2S was the rate-controlling step at reaction temperature below 500 K, whereas H2S desorption dominates the overall reaction rate at higher temperatures. The apparent activation energy of HDS reaction decreased considerably from 195 to 48 kJ/mol at reaction temperature range of 400–800 K. The reaction orders in SO2 and H2 increased with rising temperature, reaching 0.15 and 1.0, respectively, at 800 K.

Ultrasonication-assisted synthesis of 2D porous MoS2/GO nanocomposite catalysts as high-performance hydrodesulfurization catalysts of vacuum gasoil: Experimental and DFT study

In this study, a novel, simple, high yield, and scalable method is proposed to synthesize highly porous MoS2/graphene oxide (M−GO) nanocomposites by reacting the GO and co-exfoliation of bulky MoS2 in the presence of polyvinyl pyrrolidone (PVP) under different condition of ultrasonication. Also, the effect of ultrasonic output power on the particle size distribution of metal cluster on the surface of nanocatalysts is studied. It is found that the use of the ultrasonication method can reduce the particle size and increase the specific surface area of M−GO nanocomposite catalysts which leads to HDS activity is increased. These nanocomposite catalysts are characterized by XRD, Raman spectroscopy, SEM, STEM, HR-TEM, AFM, XPS, ICP, BET surface, TPR and TPD techniques. The effects of physicochemical properties of the M−GO nanocomposites on the hydrodesulfurization (HDS) reactions of vacuum gas oil (VGO) has been also studied. Catalytic activities of MoS2-GO nanocomposite are investigated by different operating conditions. M9-GO nanocatalyst with high surface area (324 m2/g) and large pore size (110.3 Å), have the best catalytic performance (99.95%) compared with Co-Mo/γAl2O3 (97.91%). Density functional theory (DFT) calculations were also used to elucidate the HDS mechanism over the M−GO catalyst. It is found that the GO substrate can stabilize MoS2 layers through weak van der Waals interactions between carbon atoms of the GO and S atoms of MoS2. At both Mo- and S-edges, the direct desulfurization (DDS) is found as the main reaction pathway for the hydrodesulfurization of DBT molecules.

Synthesis of Few Layer Amorphous 1T/2H MoS2 by a One-Step Ethanol/Water Solvothermal Method and Its Hydrodesulfurization Performance

Few layer (< 5 layers) MoS2 mixed with a 1T phase has the characteristics of a large specific surface area and an improved active site distribution. Therefore, it has been increasingly study for the catalytic hydrodesulfurization of polycyclic compounds. In this paper, few-layer MoS2 with a high proportion of the 1T phase is synthesized by a one-step solvothermal method using a green non-toxic ethanol/water solvent. Results show that few-layer MoS2 (3–5 layers) with a 1T phase up to 48% can be synthesized in a 50% ethanol solvent. This MoS2 is used to catalyse the hydrodesulfurization reaction of dibenzothiophene, and the target product conversion rate reaches 84.2%. Among them, biphenyl accounts for 70.2%, phenylcyclohexane accounts for 13.9%, and bicyclohexane accounts for 0.4%. According to the Hansen solubility parameter (HSP) distance Ra, the effects of solvents on the structure and morphology of MoS2 and the conversion of dibenzothiophene hydrodesulfurization are determined. This work is significant for the synchronous synthetic exfoliation of MoS2 with a controllable number of layers, a higher ratio of the 1T phase and good catalytic HDS of polycyclic compounds. Few layers and high proportion of 1T phase MoS2 by solvothermal synthesis for catalytic hydrodesulfurization of dibenzothiophene.