Dibenzothiophene Reaction Research Articles

Boosting oxidative desulfurization from liquid fuels with CuO-MgO assisted by MgMoO4 co-catalyst

Developing a highly efficient catalyst is one of the important topics in the field of oxidative desulfurization from liquid fuels. In this study, the composite metal oxide catalysts (CuO-MgO) with co-catalyst MgMoO4 were prepared by co-precipitation method with simple process, high efficiency and good performance and their structures characterized. An efficient extractive catalytic oxidative desulfurization (ECODS) system for liquid fuel was successfully developed on the basis of as-prepared CuO-MgO-MgMoO4 (CuMgMo) as the catalyst, sodium hypochlorite (NaClO) as the oxidant, and acetonitrile as the extractant. Taking the n-decane and n-tetradecane containing dibenzothiophene (DBT) as the test model oil sample, the main parameters influencing desulfurization performance were examined in detail, such as the molybdenum content, the dosage of CuMgMo, the reaction temperature, the initial S-concentration, the different extractants, the volume ratio of extractant to oil, the different oxidants, and the molar ratio of NaClO to DBT. Based on optimized desulfurization reaction conditions, the model oil containing different sulfur compounds (benzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene) and the real oil (straight-run gasoline, straight-run kerosene, and straight-run diesel) were further tested. Based on the free radical trapping experiments and the calculation of density functional theory, the reaction mechanism was deeply explored. The results showed that the de-electron reaction of DBT was mainly catalyzed by MgMoO4 and the reaction of HClO obtaining electron was mainly catalyzed by CuO. MgMoO4 plays an assisting role in improving the catalytic reaction rate. This work will provide a useful reference for the construction of efficient ECODS system using composite metal oxides.

Targeted fabrication of 1T-MoS2 enriched nanosheets vertically oriented on spiny-shaped nanospheres with sufficient sulfur vacancies and “rim” sites for co-enhancing the hydrodesulfurization activity and hydrogenation selectivity

The 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets over the surface was successfully prepared with the novel solvent induced micelle-limited Mo-CTA+ composites self-assembly (SIMMS) strategy under the dual effects of mixed sulfur sources (thiourea and thioacetamide) and cetyltrimethylammonium bromide (CTAB). In the proposed strategy, the molybdenum source and CTAB are firstly assembled to Mo-CTA+ by strong electrostatic attraction to avoid the molybdenum source from polymerization and forming large polymolybdate anions. Meanwhile, the CTAB moleculars self-assemble to spherical micelles, which can adsorb Mo-CTA+ through van der Waals force and obtain spherical precursors with a controllable number of nucleation sites. Under the sulfurization from mixed sulfur source, appropriate reducibility can control the formation of crystal seeds and crystal growth during the crystallization process of MoS2, whereas CTAB can regulate and control the growth behavior and micro-morphology of MoS2, which is ultimately also retained between the MoS2 nanolayersto expand their interlayer spacing and stabilize the 1T phase. Therefore, the 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets can be controllably prepared. In the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) over these catalysts, the MoS2-75%/0.25 catalyst with the highest concentration of sulfur vacancies as well as “rim” and “rim-like” sites can reach the highest HDS activity (99.1%) and HYD/DDS ratio (4.76), which are much higher than those of the MoS2-H catalyst prepared by conventional hydrothermal method (HDSDBT%=46.0%, HYD/DDS ratio=0.90).

Hydrodesulfurization over NiMo Catalysts Supported on Yolk‐shell Silica Materials with Controllable Cavity Size

AbstractNovel yolk‐shell (YS) mesoporous silica materials with different cavity sizes were successfully synthesized. Aluminium was bridged into the yolk‐shell framework of silica by a post synthesis method to improve the acidity of YS, namely Al‐YS. The corresponding NiMo/Al‐YS catalysts were also fabricated and used in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) and 4,6‐dimethyldibenzothiophene (4,6‐DMDBT). The NiMo/Al‐YS catalyst with the cavity size of 154 nm (NiMo/Al‐YS‐154) exhibits the superior conversions of DBT (99.2 %) and 4,6‐DMDBT (96.1 %) at 340 °C, 4.0 MPa, 10 h−1, highest kHDS (13.4×10−4 mol g−1 h−1 for DBT and 8.9 mol g−1 h−1 for 4,6‐DMDBT) and highest TOF for DBT (3.7 h−1) and 4,6‐DMDBT (2.3 h−1) among the investigated catalysts. The appropriate cavity size of NiMo/Al‐YS‐154 catalyst plays the key role in obtaining its superior HDS catalytic performance. Furthermore, the possible reaction networks of DBT and 4, 6‐DMDBT HDS over NiMo/Al‐YS‐x catalysts were also presented.

Non-metal doping Ni@C as highly efficient and stable hydrodesulfurization catalysts for clean liquid fuels

The development of highly efficient non-sulfide hydrodesulfurization (HDS) catalyst is still an extremely urgent and challenging matter for the ultra-deep HDS of crude oils. Based on the strategy of non-metal doping and incorporation of carbon, Ni2P@C, Ni2Si@C, and NiS2@C catalysts are successfully prepared through temperature-programmed route using MOF-derived Ni@C as precursor and investigated on the HDS of dibenzothiophene. The Ni2P@C sample has the highest HDS performance and the rate constant is 3.890 min−1, which corresponds to a 6-fold enhancement of that over Ni@C catalyst. While the Ni2Si@C catalyst corresponds to a 1.3-fold enhancement of that over Ni@C catalyst. The predictable result for the NiS2@C catalyst is very low HDS activity. There is a charge transfer between Ni and P or Si, which promotes the adsorption and reaction of dibenzothiophene. Moreover, the Ni2P@C catalyst shows outstanding stability during the long-term reaction after an 80 h. These results indicate that the non-metal doping and incorporation of carbon may be a powerful approach to improve the catalytic activity and improve the durability of catalyst for clean liquid fuels.

Unraveling the Role of Surface Termination in Ni2P(001) for the Direct Desulfurization Reaction of Dibenzothiophene (DBT): A Density Functional Theory (DFT) and Microkinetic Study

Achieving ultradeep desulfurization of transportation fuels dictates the removal of the last fragments of sulfur present in bulky refractory molecules such as dibenzothiophene (DBT). Improving the hydrodesulfurization (HDS) performance of the next-generation Ni2P catalyst is crucial; however, it is still unclear how a DBT direct desulfurization (DDS) reaction proceeds on different surface terminations of this material. This work aims at elucidating the influence of Ni3P-, Ni3P2-, and partially sulfided Ni3P2 (Ni3PS)-terminated surfaces of the Ni2P(001) crystal on the DDS reaction of DBT using density functional theory (DFT) computations. The scission of the first C–S bond in DBT was found to be kinetically hindered compared to the second C–S bond cleavage over the three surfaces owing to the highly stable structure of adsorbed DBT compared to the C12H9SH intermediate. Notably, the overall DBT desulfurization process is thermodynamically favorable only on the Ni3PS surface, due to the presence of the active phosphosulfide (Ni–P–S) phase. Microkinetic modeling was conducted to probe the reaction orders, apparent activation energy, and rate-controlling steps as a function of temperature. Notably, the ring-opening step of DBT, via the first C–S bond cleavage, is the rate-controlling step on Ni3P and Ni3PS surfaces, which is rationalized by the high energy barrier of this step. The activation energy of the reaction over the surfaces followed the order Ni3P < Ni3PS < Ni3P2. Compared to the bare Ni3P2 surface, the lower activation energy on the Ni3PS surface is explained by the destabilization effect of the reaction intermediates on the latter. Thus, the partially sulfided Ni3P2 provides a better model for the DBT desulfurization process than the fresh Ni3P2 surface.

Construction of bifunctional 3-D ordered mesoporous catalyst for oxidative desulfurization

The development of catalysts with the functions of catalyzing the oxidation of organosulfur and separating the products from reaction mixturesis facilitates to achieve high-efficiency oxidative desulfurization (ODS) of fuel. Herein, the MoO3 nanoparticles (mean diameter = 1.33 nm) confined in Ti-doped KIT-6 could be synthesized by triblock copolymer (EO20PO70EO20)-assisted in-situ synthesis method combined with stepwise pyrolysis. The prepared catalyst (Mo/KIT-6-Ti) exhibited excellent ODS performance. When cumene hydroperoxide (CHP) was used as the oxidant, Mo/KIT-6-Ti not only could completely remove dibenzothiophene (DBT) in the model gasoline at room temperature in 40 min but also had the excellent ability to adsorb and separate the sulfone product from the model gasoline. After five reaction-regeneration cycles, the DBT conversion over Mo/KIT-6-Ti still reached above 99% in 60 min. Furthermore, kinetic studies revealed that the oxidation reaction of DBT on Mo/KIT-6-Ti had extremely low activation energy (34.9 kJ/mol). Data from radical scavenger experiments suggested that hydroxyl radicals play a dominant role in the ODS. This catalyst has the potential to negate the need for a solvent extraction step in fuel desulfurization and produce ultralow sulfur fuel.

Influence of UV Radiation on the Process of Noncatalytic Oxidation of Dibenzothiophene in Dibenzothiophensulphone by the Oxygen in Air

Oxidation of dibenzothiophene (DBT) is used as the model reaction in studying the process of catalytic oxidative desulfurization of diesel fuel. The method of oxidative desulfurization includes the stage of oxidation of thiophene compounds contained in the fuel into the corresponding thiophenesulfones, followed by their extraction from the reaction mixture with a polar liquid. In this paper, we study the oxidation reaction of DBT into DBT sulfone in a solution in octane, with atmospheric oxygen in the presence of benzaldehyde at room temperature and irradiation of the reaction mixture with ultraviolet (UV) light. It is shown that in this case a DBT conversion of 97 to 98% can be achieved without using a catalyst. It is also found that UV irradiation of the reaction mixture can be carried out periodically (in pulses of a duration of 1 min), which makes it possible to exclude overhearing reaction mixture.

Titanium-Modified MIL-101(Cr) Derived Titanium-Chromium-Oxide as Highly Efficient Oxidative Desulfurization Catalyst

A titanium-chromium-oxide catalyst was prepared by a facile calcination of titanium-modified MIL-101(Cr). The resulting material, possessing a surface area of 60 m2 g−1 and a titania content of 50.0 wt%, can be directly used as the catalyst for oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT). This novel ODS catalyst can remove 900 ppm sulfur-containing compounds in a reaction time of 30 min at 60 °C. The experimental results showed that the specific activity increased with the titanium content. The specific activity of the catalyst with 50%Ti reached 129 μmol/m2, which was much higher than that of reported Ti-based catalysts.

Polyoxometalate-based 3DOM ZrO2 material for deep oxidative desulfurization of DBT with ultrahigh stability

Highly ordered three-dimensional (3DOM) macroporous polyoxometalate (POM)-based zirconia hybrids with relatively high surface area and interconnected pore structure have been fabricated by colloidal crystal template method. Owing to the evenly distributed POM active sites, large-scaled 3D ordered macroporous structure, and high porosity of as-synthesized POM-based ZrO2 composite, it exhibits excellent extractive-oxidative desulfurization activity and recyclability. 500 ppm of dibenzothiophene (DBT) in the model fuel can be removed within 2 h under mild conditions and no obvious loss of catalytic activity even after 20 times. The oxidative reaction of DBT follows pseudo-first-order kinetics, corresponded to an Arrhenius activation energy of 61.1 kJ/mol.

Novel NiMoW-clay hybrid catalyst for highly efficient hydrodesulfurization reaction

Novel NiMoW-clay hybrid composites are easily prepared by using organic cations modified clay montmorillonite (organo-MMT) as support. And the active component metal ions could be easily uniformly dispersed into interlayer space of organo-MMT. The as-fabricated hybrid catalyst exhibits substantially improved activity for hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) with the sulfur removal of 99.8%. In addition, this catalyst also shows outstanding HDS activity with the sulfur removal of 99.8% and wonderful stability during 168 h for industrial kerosene (2400 ppm S).

Influence of titanium oxide on the performance of molybdenum catalysts loaded on zeolite toward hydrodesulfurization reactions

In this work, molybdenum, cobalt, and vanadium (MCV) based catalysts were loaded on zeolite Y (Z) and modified with different ratios of titanium oxide (0, 5 and 10%) as co-support (ZT). The catalysts were characterized using a scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), electron dispersive x-ray spectroscopy (EDX), powder x-ray diffraction (XRD), N 2 adsorption-desorption isotherm, Fourier-transform infrared spectroscopy (FTIR), and temperature-programmed desorption (TPD). The prepared catalysts were evaluated for the hydrodesulfurization (HDS) reactions of dibenzothiophene (DBT). The incorporation of titania within the Z support was used to enhance the interaction between the active phases and the support surface through better distribution of the catalyst nanoparticles on the composite support. From the BET measurements, all of the catalysts exhibited the type IV isotherm with micro/mesoporous contributions. TPD was applied to illustrate the calcined catalyst acidity, which confirmed the positive role of titania in increasing the acidic strength of the catalyst. The XRD demonstrated the introduction of titania to the support which is clear from the characteristic peaks of titania. The elemental compositions of the catalyst and dispersion on the support surface were confirmed by EDX and x-ray mapping. The catalytic performance of 5% and 10% titania (ZT5-MCV and ZT5-MCV) showed higher activity compared to the control catalyst without titania (Z-MCV). A comparison of this catalyst with those reported in the literature points out that it is a promising candidate for fuel HDS. • MoCo-Zeolite/titania showed excellent hydrodesulphurization of dibenzothiophene. • Direct desulfurization mechanism was dominant based on characterization results and GC-SM. • The work is offering a convenient approach to prepare an effective HDS catalyst.

Creation of Active Sites in MOF‐808(Zr) by a Facile Route for Oxidative Desulfurization of Model Diesel Oil

AbstractMOF‐808(Zr) as an important member of metal‐organic frameworks (MOFs) has attracted much attention due to its good stability, large surface area and rich zirconium metal centers. However, Zr sites in the structure of MOF‐808(Zr) are inactive in many catalytic reactions due to they are well coordinated with organic ligands like 1,3,5‐benzenetricarboxylic acid (BTC) and formate anions. Thus, removing formate anions have been attempted to create more active sites in the structure for many reactions while maintaining the structural stability. In this work, we report that the formate ligands in MOF‐808(Zr) can be facilely removed by the treatment in hot ethanol for 4 h. The obtained material as a heterogeneous catalyst exhibited superior catalytic activity in the oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT) compared with reported MOFs catalysts. The conversion of DBT in model diesel oil could reach &gt;99 % within a reaction time of 20 min at 323 K, which is five times as that over parent MOF‐808(Zr). As a result, the sulfur content was decreased from 1000 ppm to less than 10 ppm. Such catalytic performance should be mainly attributed to the creation of more active sites in the structure of MOF‐808(Zr) after the removal of formate anions.

Carbon nanofiber-doped zeolite as support for molybdenum based catalysts for enhanced hydrodesulfurization of dibenzothiophene

Zeolite (Z) doped carbon nanofiber (CNF) was prepared as a support for a molybdenum (Mo) based catalyst and cobalt (Co) or nickel (Ni) were used as a promoter. The catalytic behavior of the synthesized catalyst zeolite-CNF/MoCo (ZFMoCo) or zeolite-CNF/MoNi (ZFMoNi) was evaluated for the hydrodesulfurization (HDS) reaction of dibenzo-thiophene (DBT) and compared with the catalyst without CNF (ZMoNi and ZMoCo). A set of characterizations were used to illustrate the physico-chemical properties of the catalyst. The catalytic activity of the catalyst was compared to the reference catalyst without CNF, and it was found that CNF has an effective role in improving the activity for sulfur removal from 90% (ZMoNi) to 95% (ZFMoNi) and from 92% (ZMoCo) to 98% (ZFMoCo). This could be due to the enhancement in the surface area after doping the CNF. Increasing the area for the dispersion of the active phase on the composite support surface (Z-CNF) showed higher catalytic performance.

Mesoporous zirconium–silica nanocomposite modified with heteropoly tungstophosphoric acid catalyst for ultra‐deep oxidative desulfurization

An adsorbent catalyst was proposed to reduce the leaching of active species of the catalyst and enhance the kinetics of the oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT) from model diesel fuel. By loading phosphotungstic acid (HPW) species onto a zirconium‐modified hexagonal mesoporous silica (Zr‐HMS), a novel catalyst was synthesized and utilized for the ODS process. An ultrafast ODS kinetics was specifically identified using 20%HPW/Zr‐HMS as catalyst. Within 30 min, more than 95% of the 350 ppm DBT content of the model fuel was oxidized by H2O2. The synthesized catalyst retained its sulfur removal ability even after five subsequent ODS reactions and the leaching of HPW species was found to be suppressed successfully. Overall, this new reusable catalyst provided an alternative for highly efficient ultra‐deep desulfurization process.

Molecular simulation of hydrodesulfurization of coal tar using Pd/ZSM‐5/γ‐Al2O3 catalyst

AbstractIn this study, all‐atom model of Pd/ZSM‐5/γ‐Al2O3 was developed and validated by comparing the experimental results of nitrogen adsorption isotherm, pore structure parameters, and powder X‐ray diffraction to our simulation results. Coal tar was simulated using dibenzothiophene (DBT), and tetralin (THN) in our study, and the product of coal tar hydrodesulfurization was modeled by H2S and n‐hexane (Hex). The adsorption and diffusion of the DBT, THN, and Hex on Pd/ZSM‐5/γ‐Al2O3 were investigated, and the simulation results were verified by differential thermogravimetric and X‐ray photoelectron spectroscopy results. The results demonstrated that DBT and THN mainly adsorbed to mesopores, and part of THN could also adsorb to micropores. Note that the mesopores allow the reactions of DBT, THN, and Hex to take place as they have large enough size, and micropores limit those reactions as those model molecules hardly adsorbed to micropores. In addition the acidity of the carrier weakens the heat of adsorption of H2S, making it easier to diffuse out of the catalyst and protect the active site. And our simulation results also show that the diffusion coefficient of H2S was much higher than other chemicals. As a consequence, the multichannel design and the choice of acidic carrier improved the sulfur tolerance of the catalyst.

Synergetic effect in RuxMo(1-x)S2/SBA-15 hydrodesulfurization catalysts: Comparative experimental and DFT studies

The effect of introducing Ru impurities into the MoS2 crystalline structure of the sulfided RuxMo(1-x)S2/SBA-15 catalysts have been investigated using density functional theory (DFT) calculations and the catalyst characterization by different techniques (chemical analysis (ICP-AES), temperature-programmed reduction (TPR), X-ray diffraction (XRD), N2 physisorption, DRIFTS of adsorbed pyridine (DRIFTS-Py) and X-ray photoelectron spectroscopy (XPS)). The catalyst activity was tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) reaction carried out in a batch reactor, T = 320 °C and total H2 pressure of 5.5 MPa. From electronic structure DFT calculations is was concluded that the 4d orbitals of both Mo and Ru played an important role in the catalyst optimization being the processes of transport and charge transference the most important ones. It was found that the enrichment with Ru, promotes a greater electronic participation (DOS at the Fermi level) of the different atoms in the RuxMo(1-x)S2 phase leading to metallization of the Mo ions. The catalyst activity in HDS of DBT reaction demonstrated a similar behavior to that of theoretical density of states (DOS) calculated via DFT. All bimetallic systems presented the synergetic effect between Ru and Mo in the HDS of DBT reaction over RuxMo(1-x)S2/SBA-15 catalysts. The highest activity observed for Ru content of x = 0.4 was consistent with theoretical results predicting that the optimum DOS contributions should be around x = 0.44. The most active Ru0.4Mo0.6S2/SBA-15 exhibit the best hydrogenation properties linked with the Ru-induced metallization of Mo ions in the Ru0.4Mo0.6S2 phase. This catalyst showed two-fold higher hydrogenation properties than CoMoS/γ-Al2O3 reference catalyst. The linear dependencies of initial activity on Brønsted-to-Lewis acidities ratio (from DRIFT-Py) and total metal surface exposure (from XPS) were observed.

Catalytic oxidative desulfurization of model and real diesel over a molybdenum anchored metal-organic framework

In this work, we report the catalytic performance of a MoO2Cl2 anchored metal-organic framework, [email protected], in the oxidative desulfurization (ODS) process on a continuous fixed-bed reactor. [email protected] was examined as a catalyst in the oxidation of model oils containing dibenzothiophene (DBT), benzothiophene (BT) or 4,6-dimethyldibenzothiophene (4,6-DMDBT). In a 50-h ODS reaction of DBT at 70 °C, with tert-butyl hydroperoxide (TBHP) as the oxidant, a constant high DBT conversion of nearly 80% was observed along with a high oxidant utility of over 85%, where DBT was converted rapidly into DBT sulfone. XRD and ICP analysis show that the structure of [email protected] was well preserved, with no significant leaching of Mo species. In addition, [email protected] can also oxidize a hydrogenated diesel oil, and 74% sulfur removal efficiency was achieved, with an extraction recovery of 92.5% after acetonitrile extraction. Spectroscopic characterization confirmed the formation of a molybdenum peroxide complex from MoO2Cl2 under TBHP treatment, a plausible catalytic process was proposed based on the experiment evidence as well as FT-IR and FT-FIR characterization results.

Kinetic and Mechanistic Analysis of Dibenzothiophene Hydrodesulfurization on Ti-SBA-15–NiMo Catalysts

MoS2-based catalysts are the most commonly used systems for the hydrodesulfurization (HDS) process on an industrial scale. Different methods were employed to enhance the efficiency of the catalysts, which include changes in catalyst support and doping agents as well as tuning the dispersion of the MoS2 phase using various synthetic techniques. In this work, we report the kinetic and mechanistic analysis of HDS of dibenzothiophene (DBT) for different NiMo-supported Ti-SBA-15 catalysts prepared by (1) direct single-pot (SP) synthesis and (2) impregnations of the NiMo phase into the Ti-SBA-15 support. Both methods were also repeated with and without the citric acid (CA) loading to achieve higher dispersion of the active metal sites. Kinetic modeling was performed to two “parallel–series” reactions of DBT, direct desulfurization (DDS) and hydrogenation (HYD), both leading to the final product of cyclohexylbenzene. Kinetic analysis reveals the considerable influence of the catalyst preparation methods to both ...

Study of the impregnation of NiMo assisted by chelating agents for hydrodesulfurization-supported catalysts over mesoporous silica

Abstract

Catalytic oxidative desulfurization of DBT using green catalyst (Mo/MCM-41) derived from coal fly ash

Current study presents the synthesis of mesoporous silica material (MCM-41) derived from coal fly ash as a catalyst support material for the catalytic oxidative desulfurization (ODS) of liquid fuels. In this work, molybdenum active species were incorporated into the mesoporous silica (Mo/MCM-41) by the incipient wet-impregnation process. The obtained Mo/MCM-41 was characterized by FESEM, HRTEM, XRD, and FT-IR to confirm its structure and functional groups present on the catalyst. Characterization study revealed that mesoporous silica was successfully synthesized from coal fly ash. Desulfurization of dibenzothiophene (DBT) containing model fuel was investigated by using synthesized catalyst, approximately 94% of DBT removal was achieved by optimizing the influencing parameters of ODS process. The ODS results proved that Mo/MCM-41 could be the potential catalyst for reduction of DBT from liquid fuels. Oxidative reaction of DBT follows the pseudo first order reaction kinetic. DBT oxidation mechanism was proposed.