V-Mo based catalysts for oxidative desulfurization of diesel fuel

Catalytic oxidative desulfurization (ODS) of a Mexican diesel fuel on a spent HDS catalyst, deactivated by metal deposits, was carried out during several reactive-batch cycles in order to study the catalytic performance to obtain low sulfur diesel. To explain catalytic activity results, Mo and/or V oxides supported on alumina pellets were prepared and evaluated in the ODS of a model diesel using tert-butyl hydroperoxide (TBHP) or H₂O₂ as oxidant. The catalytic results show that V-Mo based catalysts are more active during several ODS cycles using TBHP. The performance of the catalysts was discussed in terms of reduced species of vanadium oxide, prevailing on the catalysts, which increase the sulfone yield of refractory HDS compounds (DBT, 4-MDBT and 4,6-DMDBT).     

Complete oxidation of 2-propanol over gold-based catalysts supported on metal oxides

This paper concerns the preparation of metal oxide-supported gold catalysts and their application to 2-propanol abatement in order to lower the light off temperature. Catalytic oxidation of 2-propanol was investigated on Au/CeO₂, Au/Fe₂O₃, Au/TiO₂ and Au/Al₂O₃ catalysts prepared from the deposition–precipitation (DP) method. The catalysts are characterized by XRD (X-ray diffraction), BET (Brunner–Emmett–Teller), TEM (transmission electron microscopy), NH₃-TPD (NH₃-temperature programmed desorption), H₂-TPR (H₂-temperature programmed reduction), ICP-AES (inductively coupled plasma-atomic emission spectroscopy) and XPS (X-ray photoelectron spectroscopy) techniques. The catalytic activity of Au/metal oxide samples towards the deep oxidation of 2-propanol to CO₂ and water has been found to be strongly dependent on the kind of supports, the amount of gold loading, the calcination temperature and the moisture content in the feed.     

In situ synthesis of Au/Ti-HMS and its catalytic performance in oxidation of bulky sulfur compounds using in situ generated H2O2 in the presence of H2/O2

Gold particles are supported on Ti-containing mesoporous silica (Ti-HMS) through an in situ process. The obtained samples were characterized by a series of techniques including ICP, powder X-ray diffraction, N₂ sorption, UV-visible spectroscopy and transmission electron microscopy. The performance of the catalyst in direct synthesis of H₂O₂ from H₂/O₂ in methanol solvent and oxidative desulphurization using the in situ generated H₂O₂ have been systematically investigated. The results show that in situ synthesized Au/Ti-HMS, the organic template of which is eliminated via extraction with ethanol, successfully maintains the typical wormhole structure of HMS and possesses uniform mesopores, which is confirmed by N₂ sorption and TEM. UV-visible spectroscopy result confirms the simultaneous existence of Au and Ti active centers in this bifunctional catalyst. Gold particles supported on Ti-HMS show high activity in the direct synthesis of H₂O₂ from H₂ and O₂ in methanol solvent. Furthermore, high removal rate of bulky sulfur compounds can be obtained using the in situ generated H₂O₂ over Au/Ti-HMS. Final conversion rate of the substrates confirms the dominant role of the in situ H₂O₂ oxidation in deep desulphurization. In addition, this bifunctional catalyst can avoid the insufficiency of H₂O₂ caused by the decomposition comparing with the Ti-HMS/commercial H₂O₂ system.     

Deep desulfurization of fuels catalyzed by surfactant-type decatungstates using H2O2 as oxidant

Oxidation of dibenzothiphene (DBT) in model oil with H₂O₂ using surfactant-type decatungstates Q₄W₁₀O₃₂ (Q = (CH₃)₃NC₁₆H₃₃, (CH₃)₃NC₁₄H₂₉, (CH₃)₃NC₁₂H₂₅ and (CH₃)₃NC₁₀H₂₁) as catalysts was studied. The surfactant-type decatungstates were synthesized and characterized. The suitable reaction condition of deep desulfurization was suggested: n(DBT):n(catalyst):n(H₂O₂) = 1:0.01:3, 60 °C for 0.5 h, under which the DBT conversion can reach 99.6% with [(CH₃)₃NC₁₆H₃₃]₄W₁₀O₃₂ as catalyst. The length of carbon chains of quaternary ammonium cations played a vital role in the catalytic activity of surfactant-type decatungstates, that is, the longer the carbon chain of quaternary ammonium cation of a catalyst was, the better the activity of this catalyst showed. [(CH₃)₃NC₁₆H₃₃]₄W₁₀O₃₂ exhibited the best catalytic performance and can be recycled for six times without significant decrease in catalytic activity. Using benzothiphene (BT) and 4,6-dimethyldibenzothiphene (4,6-DMDBT) as substrates in model oil, surfactant-type decatungstates also showed high catalytic activity. During desulfurization process, BT conversion can reach 99.6% at 3.25 h, while 99.4% of 4,6-DMDBT conversion reached at 1.25 h, with the temperature of 60 °C under atmospheric pressure. The sulfone can be separated from the oil using N,N-dimethylformamide (DMF) as an extractant, and the sulfur content can be lowered from 1000 to 4 ppm. For real diesel, the sulfur removal can reach 93.5% after five times extraction.     

Activity and stability of amino-functionalized SBA-15 immobilized 12-tungstophosphoric acid in the oxidative desulfurization of a diesel fuel model with H2O2

In this study, the stability and the catalytic activity of an ordered mesoporous SBA-15 immobilized 12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) in the oxidative desulfurization (ODS) of benzothiophene (BT) and dibenzothiophene (DBT) were improved by a post-synthesis-grafting method. In this method, SBA-15 was functionalized to provide a large number of amine groups for the immobilization of HPW through electrostatic binding with (3-aminopropyl) triethoxysilane (APTES) using triflic acid as a protonated agent. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results show that the structure of functionalized SBA-15 support and the active phase of the HPW remained intact after immobilization. The synthesized PW^–H₃N⁺-SBA-15 catalyst showed a high catalytic activity for ODS, achieving BT and DBT conversion of 99.9% and 100% with the reaction conditions of reaction temperature of 50?°C, H₂O₂ dosage of 1?mL, catalyst dosage of 0.03?g, and reaction time 5 and 1?h, respectively. The catalyst also showed a high reusability after up to four cycles, for which the conversion of the fourth reaction was 90.0% for both BT and DBT.     

Effects of preparation conditions in hydrothermal synthesis of highly active unsupported NiMo sulfide catalysts for simultaneous hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Unsupported NiMo sulfide catalysts were prepared from ammonium tetrathiomolybdate (ATTM) and nickel nitrate by using a hydrothermal synthesis method involving water, organic solvent and hydrogen. The activity of these catalysts in the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was much higher than that of the commercial NiMo/Al₂O₃ sulfide catalysts. Interestingly, the unsupported NiMo sulfide catalysts showed higher activity for hydrogenation (HYD) pathway than the direct desulfurization (DDS) pathway in the HDS of DBT. The same trends were observed for the HDS of 4,6-DMDBT. Morphology, surface area, pore volume and the HDS activity of unsupported NiMo sulfide catalyst depended on the catalyst preparation conditions. Higher temperature and higher H₂ pressure and addition of an organic solvent were found to increase the HDS activity of unsupported NiMo sulfide catalysts for both DBT and 4,6-DMDBT HDS. Higher preparation temperature increased HYD selectivity but decreased DDS selectivity. High-resolution TEM images revealed that unsupported NiMo sulfide prepared at 375 °C shows lower number of layers in the stacks of catalyst with more curvature and shorter length of slabs compared to that prepared at 300 °C. On the other hand, higher preparation pressure increased DDS selectivity but decreased HYD selectivity for HDS of 4,6-DMDBT. HRTEM images showed higher number of layers in the stack for the NiMo sulfide prepared under an initial H₂ pressure of 3.4 MPa compared to that under 2.1 MPa. The optimal Ni/(Mo + Ni) ratio for the NiMo sulfide catalyst was 0.5, higher than that for the conventional Al₂O₃-supported NiMo sulfide catalysts. This was attributed to the high dispersion of the active species and more active NiMoS generated. The present study also provides new insight for controlling the catalyst selectivity as well as activity by tailoring the hydrothermal preparation conditions.     

Direct synthesis of hydrogen peroxide from H2/O2 and oxidation of thiophene over supported gold catalysts

Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed over supported gold catalysts. The catalysts were characterized by means of UV–vis, H₂-TPR, TEM and XPS. Based on the results we conclude that metallic Au is the active species in the direct synthesis of hydrogen peroxide from H₂ and O₂. During preparation process of catalyst by deposition–precipitation with urea, the pH value increased and the gold particle size decreased with increasing the urea concentration. The catalyst prepared with higher urea concentration showed a higher activity and its stability also was efficiently improved. Gold nanoparticles, supported on TiO₂ or Ti contained supports, gave a higher catalytic activity. Thiophene can be efficiently oxidized by hydrogen peroxide synthesized in situ from H₂ and O₂ over Au/TS-1.     

The preparation of Au/CeO2 catalysts and their activities for low-temperature CO oxidation

Au/CeO₂ catalysts prepared by co-precipitation (CP) and deposition-precipitation (DP) methods were tested for low temperature CO oxidation reaction. The structural characters and redox features of the catalysts were investigated by XRD, XPS and H₂-TPR. Their catalytic performances for low temperature CO oxidation were studied by means of a microreactor -GC system. It showed that the catalytic activities of Au/CeO₂ catalysts greatly depended on the preparation method. The catalysts prepared by DP method exhibited a surprisingly higher activity towards CO oxidation than that prepared by CP method. This may arise from the differences in the particle sizes of Au and redox properties of the catalysts. The low Au loading and the resistance to high temperature of DP-prepared catalyst made it more applicable.     

Oxidative desulfurization of diesel fuel by mesoporous phosphotungstic acid/SiO2: the effect of preparation methods on catalytic performance

Two kinds of mesoporous phosphotungstic acid/SiO₂ (HPW/SiO₂) have been synthesized by amino-functionalized (AF) method and evaporation-induced self-assembly (EISA) method, and their catalytic performance was investigated for deep oxidative desulfurization of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in diesel oil. Various analysis techniques such as XRD, TEM, N₂ adsorption/desorption isotherms, FT-IR and ³¹P MAS NMR spectra have been used to investigate the pore structure and chemical properties of the resultant catalysts. The structural and spectroscopic analysis indicates both catalysts have a highly ordered 2D hexagonal mesostructure. HPW/SiO₂-EISA can maintain the Keggin structure of HPW molecules and has a high BET surface area (403 m²/g). But in the AF method, the mesostructure of SBA-15 are partially blocked after the introduction of HPW molecules, and the Keggin structure of HPW molecules has been damaged. The catalytic performance results also show that HPW/SiO₂-EISA exhibits higher catalytic activity and stability compared to HPW/SiO₂-AF. As for HPW/SiO₂-EISA, the conversions of DBT, 4,6-DMDBT and BT are found to be 99.6, 97.6, 94.8 %, respectively. It shows a good maintenance of activity even after the 7th cycle of use. While corresponding conversions by using HPW/SiO₂-AF are found to be 90.2, 89.1 and 87.6 %, and the DBT conversion decreases to 75.7 % after the 5th cycle of use.     

HDS reactivities of dibenzothiophenic compounds in a LC-finer LGO and H2S/NH3 inhibition effect

The hydrodesulfurization (HDS) reactivities and the inhibition effects of H₂S and NH₃ were experimentally investigated for 11 difficult-to-remove sulfur compounds contained in LC-finer light gas oil using a commercial NiMo/Al₂O₃ hydrotreating catalyst. Among these sulfur compounds, 4-MDBT was the most reactive while 4,6-DMDBT was the least reactive. It was found that the presence of methyl groups away from the sulfur atom slightly enhanced the HDS reactivities of the methyl substituted DBTs. The observed low reactivity of 4,6-DMDBT was mainly caused by the steric hindrance of the two methyls at the 4 and 6 positions. Both H₂S and NH₃ significantly inhibited the HDS reaction rates for all 11 sulfur species of interest, while 4,6-DMDBT was one of the most inhibited species. At the same concentration (1.0 vol%), H₂S showed a stronger inhibition effect than NH₃. Measurable catalyst deactivation was observed in the course of the experiment that had a relatively even effect on the HDS of all reactants investigated in this study.     

Oxidative Desulfurization of Model Oil over Au/Ti-MWW

Au/Ti-MWW catalysts were prepared by the impregnation of HAuCl₄ on Ti-MWW. Its structure and properties were characterized by X-ray diffraction, N₂ adsorption and UV-visible. The oxidation reactions of thiophene (TH), benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyl-dibenzothiophene (DMDBT) were investigated at mild reaction conditions using H₂O₂ as oxidant. The results showed that Au loading could significantly promote the activity of Ti-MWW for oxidative desulfurization.     

Polyoxometalate-based ionic liquids as catalysts for deep desulfurization of fuels

In order to obtain the ultra low-sulfur diesel, deep desulfurization of diesel oil has become a vital subject of environmental catalysis studies. Extraction and catalytic oxidation desulfurization (ECODS) system is one of the most promising desulfurization processes. A series of Keggin-type POM-based ionic liquids hybrid materials [MIMPS]₃PW₁₂O₄₀·2H₂O (1-(3-sulfonic group) propyl-3-methyl imidazolium phosphotungstate), [Bmim]₃PW₁₂O₄₀ (1-butyl 3-methyl imidazolium phosphotungstate), [Bmim]₃PMo₁₂O₄₀ (1-butyl 3-methyl imidazolium phosphomolybdate) and [Bmim]₄SiW₁₂O₄₀ (1-butyl-3-methyl imidazolium silicotungstate) have been developed in this study, and the reaction has performed using the POM-ILs materials as catalysts, H₂O₂ as oxidant, and ionic liquid (IL) as solvent. Through experimental evaluations, [MIMPS]₃PW₁₂O₄₀·2H₂O was found to be the best catalyst, with an S-removal of 100% at 30 °C for 1 h. The main factors affecting the process including temperature, catalyst dosage, and O/S (H₂O₂/DBT) molar ratio were investigated in detail. Under the optimal conditions, DBT (dibenzothiophene) and 4,6-DMDBT (4,6-dimethyl-dibenzothiophene) could achieve high desulfurization efficiency. Moreover, the reaction system also exhibited high activity in actual diesel oil, which could be reduced from 1113 ppm to 198 ppm. The reaction system could recycle 8-times with a slight decrease in activity.     

Deep oxidative desulfurization of model fuel using ozone generated by dielectric barrier discharge plasma combined with ionic liquid extraction

The dielectric barrier discharge (DBD) is often used to prepare ozone. In this study, a novel room temperature oxidative desulfurization method involving ozone oxidation produced in the DBD reactor combined with ionic liquid (IL) [BMIM]CH₃COO ([BMIM]Ac) extraction was developed. The method was suitable for the deep removal of sulfur (S)-containing compounds from model fuel. By this desulfurization technology, 4,6-dimethyldibenzothiophene (4,6-DMDBT), dibenzothiophene (DBT), benzothiophene (BT) and thiophene (TS) were efficiently removed. Normally, the removal of TS and BT from fuel is highly difficult. However, using the proposed method of this study without any catalyst, the removal rate of TS and BT reached 99.9%. When TiO₂/MCM-41 was used as a catalyst, the S-removal of DBT and 4,6-DMDBT increased to 98.6 and 95.2%, respectively. The sulfur removal activity of the four sulfur compounds decreased in the order of TS > BT >> DBT > 4,6-DMDBT.     

Photocatalytic oxidative desulfurization of dibenzothiophene catalyzed by amorphous TiO2 in ionic liquid

Three types of TiO₂ were synthesized by a hydrolysis and calcination method. The catalysts were characterized by X-ray powder diffraction (XRD), diffuse reflectance spectrum (DRS), Raman spectra, and X-ray photoelectron spectroscopy (XPS). The XRD and Raman spectra indicated that amorphous TiO₂ was successfully obtained at 100 °C. The results indicated that amorphous TiO₂ achieved the highest efficiency of desulfurization. The photocatalytic oxidation of dibenzothiophene (DBT), benzothiophene (BT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and dodecanethiol (RSH) in model oil was studied at room temperature (30 °C) with three catalysts. The system contained amorphous TiO₂, H₂O₂, and [Bmim]BF₄ ionic liquid, ultraviolet (UV), which played vitally important roles in the photocatalytic oxidative desulfurization. Especially, the molar ratio of H₂O₂ and sulfur (O/S) was only 2: 1, which corresponded to the stoichiometric reaction. The sulfur removal of DBT-containing model oil with amorphous TiO₂ could reach 96.6%, which was apparently superior to a system with anatase TiO₂ (23.6%) or with anatase — rutile TiO₂ (18.2%). The system could be recycled seven times without a signicant decrease in photocatalytic activity.     

Inhibition of CoMo/HMS catalyst deactivation in the HDS of 4,6-DMDBT by support modification with phosphate

A series of CoMoS catalysts supported on hexagonal mesoporous silica (HMS) modified with different amounts of phosphate (0.5, 1.0, 1.5 and 2.0 wt.%) were prepared in order to study the influence of phosphate on catalyst deactivation. The catalysts were characterized by a variety of techniques (X-ray fluorescence, N₂ adsorption-desorption at 77 K, FT-IR study of the framework vibration and NO adsorption, NH₃-TPD, H₂-TPR, XPS, ³¹P NMR and TPO/TGA). The sulfided catalysts were tested in the deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) performed in a fixed-bed flow reactor at 598 K, P = 5.0 MPa and WHSV = 46.4 h⁻¹. The catalyst with the largest phosphate content (2.0 wt.%) showed the best catalytic response linked with its low deactivation during on-stream reaction and a larger sulfidation degree of Co species. It was found that coking behavior is closely related with the location of the active sites in the support structure being a lower coke formation on the catalysts having active phases located within support structure. The catalysts modified with a large amount of phosphorous (1.5 and 2.0 wt.% of P₂O₅) were more susceptible to coking and produced a more polymerized coke than P-free sample, as confirmed by TPO/TGA experiments. The presence of P₂O₅ favours the sulfidation degree of Co species and the creation of medium strength acid sites leading to the enhancement of the 4,6-DMDBT HDS reaction toward the isomerization route.     

Efficient oxidative desulfurization (ODS) of model fuel with H2O2 catalyzed by MoO3/γ-Al2O3 under mild and solvent free conditions

An efficient process to remove organic sulfur compounds from model fuel has been explored. Dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) can be completely oxidized into their corresponding sulfones by H₂O₂ over 14 wt.% MoO₃/γ-Al₂O₃ catalyst under mild conditions in 15 min. The effects of solvent, initial sulfide concentration, loading of MoO₃ and amount of catalyst on oxidative removal of DBT were studied. The employments of solvents have decreased the reaction rate of DBT, which can be attributed to the competitive adsorption between the sulfide and solvent. The oxidative reactivity increases in the order of thiophene (Th) < benzothiophene (BT) < DBT < 4, 6-DMDBT. The catalyst can be regenerated by methanol washing at 333 K.     

Inhibition and deactivation in staged hydrodenitrogenation and hydrodesulfurization of medium cycle oil over NiMoS/Al2O3 catalyst

Hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of a commercial medium cycle oil (MCO) were performed over a commercial NiMoS/Al₂O₃ catalyst through both single- and two-stage hydrotreatments at 340°C. The reaction atmosphere was replaced with fresh hydrogen, with or without additional dose of catalyst, for the second-stage treatment to determine the mechanism of reduced activity. Sulfur and nitrogen molecular species in MCO were identified by gas chromatography with an atomic emission detector (GC-AED) to quantify their respective reactivities and susceptibilities to inhibition. Under single-stage (30 min) conditions, the reactivity orders in HDS and HDN were BT>DBT>4-MDBT>4,6-DMDBT and In>alkylIn>Cz>1-Cz>1,8-Cz, respectively. Additional reaction time beyond the initial 30 min, without atmosphere or catalyst replacement, gave little additional conversion. Replacement of the first-stage gas with fresh hydrogen strongly improved second-stage conversions, particularly those of the more refractory species. An additional dose of catalyst for the second stage with hydrogen renewal facilitated additional HDS of dibenzothiophene (DBT), 4-monomethylated DBT (4-MDBT), and 4,6-dimethylated DBT (4,6-DMDBT) which was independent of their initial reactivity, while HDN of carbazole (Cz), 1-Cz, and 1,8-Cz was improved, the least reactive species being most denitrogenated. Such results suggest the strong inhibition of the gaseous products H₂S and NH₃. The catalyst deactivation was most marked with HDN of 1,8-Cz, suggesting that acidity is essential to the reaction. H₂S is suspected to inhibit both S elimination and hydrogenation of S and N species at the level of concentration obtained during desulfurization. The inhibition by remaining substrates may still influence the HDS and HDN of refractory species in the second stage, even if their contents were reduced by the first stage. It appears very important to clarify the inhibition factor of all species on the refractory sulfur species, and to determine the inhibition susceptibility of these species at their lowered concentration to enable the effective achievement of 50 ppm sulfur level in distillate products. The conversions of inhibitors must be accounted for during reactions. Catalyst and reaction configuration to reduce the inhibition by the gaseous products are the keys for deep refining.     

Syngas production via combined oxy-CO2 reforming of methane over Gd2O3-modified Ni/SiO2 catalysts in a fluidized-bed reactor

In this research, Ni/SiO₂ catalyst was modified with different amount of Gd₂O₃ and characterized with temperature-programmed desorption of CO₂ (CO₂-TPD) and NH₃ (NH₃-TPD), temperature-programmed reduction with H₂ (H₂-TPR) and X-ray diffraction (XRD). It was found that Gd₂O₃-modified Ni/SiO₂ catalysts possessed higher CO₂ adsorption and activation ability due to the formation of surface carbonate species. H₂-TPR and XRD characterizations found that the strong interaction among nickel, Gd₂O₃ and SiO₂ took place, which improved the dispersion of Ni. Gd₂O₃-modified Ni/SiO₂ catalysts exhibited higher activity and stability for the combined oxy-CO₂ reforming of methane in fluidized-bed reactor. The H₂/CO ratio in produced syngas could be controlled via controlling reaction temperature and CO₂/O₂ ratio in feed.     

Hydrodesulfurization of hindered dibenzothiophenes on bifunctional NiMo catalysts supported on zeolite–alumina composites

A series of NiMo catalysts supported on HNaY(x)–Al₂O₃ composites with different amounts of HNaY zeolite (x = 0, 5, 10, 20 and 100 wt.% of HNaY) was prepared and tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyl-DBT (4,6-DMDBT). The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-IR spectroscopy of pyridine and nitrogen oxide adsorption (Py and NO-FT-IR), temperature-programmed reduction (TPR), scanning electron microscopy (SEM-EDX) and high-resolution transmission electron microscopy (HRTEM). It was found that the increase in the zeolite content causes changes in the acidic properties of the catalyst (number of acid sites) as well as in the characteristics of the deposited metallic species (location and dispersion). Different activity trends with the amount of the zeolite were found for the DBT and 4,6-DMDBT hydrodesulfurization on NiMo/HNaY-Al₂O₃ catalysts. As for the HDS of DBT the alumina-supported catalyst presents the highest activity. The incorporation of the zeolite causes an initial drop and then the recovery of activity with zeolite content. In contrast, for the 4,6-DMDBT the HDS activity always increases with zeolite content. These two different catalytic behaviors seem to be due to two opposite effects, which affect the contribution of the reaction routes available for the HDS of each reactant, these effects are: (i) the decrease of MoS₂ dispersion caused by the incorporation of zeolite to the catalyst and (ii) the increase of the proportion of Brönsted acid sites with zeolite content. The reaction product distribution indicates that both types of sites, coordinatively unsaturated sites (CUS) of the MoS₂ and zeolite Brönsted acid sites, participate in the 4,6-DMDBT and DBT transformations.     

Removal of thiophenic compounds from liquid fuel by different modified activated carbon cloths

The adsorption behavior of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from n-heptane was investigated onto activated carbon cloth (ACC) and its modified forms at 30 °C in batch condition. ACC was modified by HNO₃, (NH₄)₂S₂O₈, H₂SO₄, HCl and NaOH at ambient temperature. The adsorbents were characterized using nitrogen adsorption/desorption. It was found that the adsorbents are mainly microporous but differ in their surface chemistry, which is related to the effect of oxidizing agent. The adsorption process was studied from both equilibrium and kinetics point of view. The equilibrium experimental data were fitted to the Langmuir, Freundlich and Langmuir-Freundlich by non-linear method. Among the tested adsorbents, the modified ACC with HNO₃ (ACC-HNO₃) had the highest capacity for adsorption of DBT. Kinetic characterization of the adsorption process indicated that the mixed-order and modified pseudo-n-order models can describe the kinetics of adsorption of thiophenic compounds onto ACCs. The ACC and ACC-HNO₃ were used to test the removal efficiency of total sulfur contents (BT, DBT and DMDBT, 150 ppmw for each of them), too. The effect of shaking and ultrasound methods and also temperature and time on the regeneration of saturated ACC-HNO₃ with DBT was studied.