Simultaneous Hydrodesulfurization Research Articles

Synthesis, characterization, and performance evaluation of unsupported tetrametallic CoMoMnAl and CoMoZnAl catalysts for selective hydrodesulfurization (HDS)

New formulations of unsupported tetrametallic catalysts derived from layered double hydroxides (LDH) compounds were synthesized by a constant pH coprecipitation method, characterized, and evaluated in the selective hydrodesulfurization (HDS) of thiophene in the presence of cyclohexene. The layered double hydroxides were prepared using terephthalate (C8H8O2)2- as the interlayer anion with nominal aluminum molar fraction of 0.5, and nominal cobalt to MII (M = Zn or Mn) ratios of 0.2, 0.4 and 0.6. Molybdenum introduction in the LDH precursor was accomplished by an ion exchange process using the heptamolybdate anion. The calcined Mn samples showed a higher surface area than those obtained from Zn. The sulfidation was carried out in situ with a heating ramp up to 673 K and the catalysts were evaluated in a tubular flow reactor. The catalytic evaluation of Zn and Mn-based materials for simultaneous thiophene HDS and cyclohexene hydrogenation (HYD) was conducted at 573 K and 20 bar. The results show that the Zn-based unsupported catalysts synthesized here exhibited higher selectivity for the HDS reaction than an industrial one.

Enhancing simultaneous hydrodesulfurization and hydrodenitrogenation reactions: Kinetic modeling of stacked NiMoP and CoMoP catalysts beds

Stringent environmental regulations require reducing fuel sulfur content for adequate operation of vehicle emission control systems. Deep hydrodesulfurization (HDS) removes over 99 % of sulfur compounds, including the less reactive ones like 4,6-dimethyldibenzothiophene (4,6-DMDBT). However, HDS kinetics is inhibited by compounds like H2S, nitrogenous compounds, and aromatics. This article delves into kinetic modeling of concurrent hydrodesulfurization (HDS) of 4,6-DMDBT and hydrodenitrogenation (HDN) of quinoline (Q) reactions. It explored the use of stacked beds of CoMoP and NiMoP catalysts in two configurations. The effects of temperature and weight hourly space velocity (WHSV) on conversions and product yields were investigated. Higher reaction temperatures, in addition to the expected increase of 4,6-DMDBT and quinoline overall conversions, also led to an increased in hydrogenation selectivity. Kinetic models were developed for these reactions and catalysts, and kinetic parameters were estimated using a hybrid numerical procedure. The configuration where CoMoP was the first catalyst to encounter the reaction feedstock exhibited higher conversions for both reactions. The apparent activation energies for 4,6-DMDBT HDS were 99 and 41 kJ mol−1 for NiMoP and CoMoP, respectively while for HDN, values of 62 and 68 kJ mol−1 were estimated. For the adsorption enthalpy of nitrogenous compounds, values of −59 and −40 kJ mol−1 were observed for NiMoP and CoMoP, respectively.

Kinetics of simultaneous hydrodesulfurization and hydrodenitrogenation reactions using CoMoP/Al2O3 and NiMoP/Al2O3

Hydrodesulfurization (HDS) is a key reaction to achieve diesel production at the specified low sulfur levels and is highly affected by a competing reaction involving nitrogen removal through hydrodenitrogenation (HDN). This work evaluated kinetic parameters of simultaneous reactions of HDS of dibenzothiophene (DBT) and HDN of quinoline (Q) using CoMoP/Al2O3 and NiMoP/Al2O3 catalysts under operational conditions that allow a wide range of reagent conversions. Estimated parameters were evaluated using rigorous statistical analysis. Good fits for the evaluated experimental data were provided by both power-law and Langmuir-Hinshelwood models. Turnover frequency values highlight adsorption and competition effects between nitrogen-containing compounds and sulfur-containing compounds. NiMoP catalyst showed higher hydrogenating power than CoMoP, with larger absolute value of the estimated adsorption enthalpy (−120 kJ.mol−1 for NiMoP and −75 kJ.mol−1 for CoMoP), suggesting strong adsorption of nitrogen compounds. A catalyst with more hydrogenating power is also more capable of performing both HDN and HDS reactions simultaneously.

Simultaneous hydrodesulfurization of thiophene and benzothiophene over NiMoS catalysts supported on γ-Al2O3 composites containing ZSM-5

Alumina composites containing microporous ZSM-5 (Z-5) and mesoporous ZSM-5 (MZ-5), corresponding to xZA and xMZA, were developed by incorporating Z-5 and MZ-5 into γ - Al2O3, respectively. The two series of NiMoS/xMZA and NiMoS/xZA catalysts were prepared with these two composites as supports, respectively, and were used for the simultaneous hydrodesulfurization (HDS) of thiophene (T) and benzothiophene (BT). The results show that NiMoS/xMZA series catalysts exhibit higher HDS activity than that of NiMoS/xZA and NiMoS/γ-Al2O3, and the HDS activity of NiMoS/xMZA catalysts increases with the increase of MZ-5. The high HDS activity can be mainly attributed to the synergistic effects of the efficient diffusing pore channels, high dispersion of type II NiMoS phases, suitable acidity, and moderate Mo-support interaction. Moreover, the product distribution of HDS shows that the NiMoS/xMZA catalysts possess the dominant direct desulfurization (DDS) selectivity and the selectivity increases with the increase of MZ-5 content due to more corner sites and suitable Brønsted (B) acid sites, whereas the NiMoS/xZA catalysts perform more excellent hydrogenation (HYD) selectivity, and the selectivity increases with the increase of Z-5 content because of the existence of more edge sites. Based on this, the possible reaction network for T and BT hydrodesulfurization over the catalysts are proposed.

Simultaneous Hydrodesulfurization of Thiophene and Benzothiophene Over Nimos Catalysts Supported on Γ-Al2o3 Composites Containing Zsm-5

Simultaneous Hydrodesulfurization of Thiophene and Benzothiophene Over Nimos Catalysts Supported on Γ-Al2o3 Composites Containing Zsm-5

Influence of CeO2 loading on the catalytic performance of CoNiMoS/CeO2–Al2O3 toward vacuum gas oil hydrotreatment

This work investigates the effect of CeO2 doping into the CoNiMoS/Al2O3 catalyst on the efficiency of heavy vacuum gas oil (HVGO) hydrotreatment. Particularly, two supports contain 10% and 25% CeO2 to Al2O3 were prepared by co-precipitation method. Metals were subsequently loaded onto these supports via impregnation technique. The produced catalysts had been then sulfided before introduction to the hydrotretment process. Structural characteristics of supports and catalysts were verified by X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), Transmission electron microscope (TEM) and N2-physiosorption technique. Obvious variations in both morphology and values of surface features could be detected via incorporation of ceria with alumina. The10%CeO2 doped catalyst could successfully attain high percentages of simultaneous hydrodesulfurization and hydrodenitrogenation affinity: 94.8% and 95.45% respectively. This increased the catalytic activity, which had been 30% higher than of using alumina individually, could be attributed to the presence of ceria within the composition of support.

Bulk hydrotreating MonW12-nS2 catalysts based on SiMonW12-n heteropolyacids prepared by alumina elimination method

A series of unsupported mono- and bimetallic MonW12-nS2 catalysts were synthesized by alumina elimination from supported MonW12-nS2/Al2O3 samples using acid etching. Alumina supported catalysts have been in turn prepared by using monometallic H4SiMo12O40 and H4SiW12O40 heteropolyacids (HPAs), their mixture with Mo/W atomic ratio equal to 1/11 and 3/9, and mixed bimetallic H4SiMo1W11O40 and H4SiMo3W9O40 HPAs. All catalysts were characterized by N2 adsorption, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), extended X-ray absorption fine structure (EXAFS) spectroscopy and powder X-ray diffraction (XRD) and their performance were evaluated in simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of naphthalene. The etching process led to a successful removal of all the support and of the partially sulfided species, with sulfidation degrees of both Mo and W above 90 % on the final bulk solids. The active phase also underwent a rearrangement, as higher average length and stacking were measured on the bulk catalysts than on the original supported ones. Mixed MoWS2 phase was evidenced in all solids, prepared from mixed HPAs (MonW12-nS2) or from the mixture of monometallic HPAs (RefMonW12-nS2), by EXAFS and ToF-SIMS, with however a larger quantity on the MoW solids. It seems that the mixed MoWS2 phase observed on the supported MoW catalysts is maintained through the etching process, while on RefMonW12-nS2 the mixed phase, observed in a much lesser extent in the corresponding supported catalyst, could result from the aggregation of the monometallic slabs. MonW12-nS2 catalysts were found more effective than the monometallic catalysts and than the corresponding RefMonW12-nS2, in both dibenzothiophene hydrodesulfurization and naphthalene hydrogenation, which was related to the presence of the mixed phase maintained through the etching of the support.

Trimetallic NiMoW and CoMoW catalysts supported on SBA-15 modified with titania or zirconia for deep hydrodesulfurization

SBA-15, Ti-SBA-15 and Zr-SBA-15 were used to prepare trimetallic CoMoW and NiMoW catalysts in order to inquire into the effect of the support’s composition on the catalytic performance in deep hydrodesulfurization (HDS). Supports and catalysts were characterized by N2 physisorption, X-ray diffraction, temperature-programmed reduction, scanning electron microscopy (SEM-EDX) and high-resolution transmission electron microscopy. The catalytic activity was determined in the simultaneous HDS of dibenzothiophene and 4,6-dimethyldibenzothiophene. The most important characteristics of the SBA-15 material were preserved in the titania and zirconia-containing supports and the trimetallic catalysts. The deposited metal oxide species (NiO, CoO, MoO3 and WO3) were well-dispersed. NiMoW catalysts were substantially more active in deep HDS than the corresponding CoMoW ones. Titania and zirconia addition to the supports resulted in higher HDS activity of NiMoW and CoMoW catalysts, being this effect larger for the Ni-promoted samples. The NiMoW/Zr-SBA-15 catalyst was the most active for the elimination of sulfur from both dibenzothiophene and 4,6-dimethyldibenzothiophene. Its activity was twice higher than that of the NiMoW/SBA-15 analog. This was attributed to the high dispersion of the deposited metal species in the sulfided NiMoW/Zr-SBA-15 sample. Regarding the catalysts’ selectivity, it depended more strongly on the promoter used than on the support’s chemical composition.

Effects of Citric Acid Addition Method on the Activity of NiMo/γ-Al2O3 Catalysts in Simultaneous Hydrodesulfurization and Hydrodenitrogenation Reactions

Two NiMo catalysts were prepared by different methods using citric acid to assess the effects of preparation method on dibenzothiophene hydrodesulfurization (HDS) and simultaneous HDS and hydrodenitrogenation: co-impregnation and post-treatment. Characterization of oxide catalysts was performed by nitrogen physisorption, X-ray diffraction, and temperature-programmed sulfidation, while sulfided samples were characterized by temperature-programmed reduction (TPR-S) and NO chemisorption. The catalytic evaluation for HDS reaction was performed in a three-phase reactor, with and without quinoline. The direct desulfurization is the preferred route for the HDS of dibenzothiophene. The post-treatment method was more efficient in achieving higher catalytic activity than co-impregnation. Furthermore, TPR-S and NO chemisorption results show an enhancement in the density of active sites on the catalyst prepared by post-treatment, being more hydrogenating than the one synthesized by co-impregnation. Although the catalyst prepared by post-treatment was more inhibited by quinoline, it remained more active than the one synthesized by co-impregnation.

Kinetic Assessment of the Simultaneous Hydrodesulfurization of Dibenzothiophene and the Hydrogenation of Diverse Polyaromatic Structures

The elimination of sulfur from fossil fuels via hydrodesulfurization (HDS) is paramount to produce cleaner fuels. Ultradeep HDS refers to reducing sulfur in fuels below the 10 ppm level. Nevertheless, under such conditions, dibenzothiophenes (DBTs) are to be desulfurized in the presence of highly complex aromatic structures that possibly exert inhibitory effects. Therefore, this contribution presents a kinetic study of the inhibition effect of diverse aromatic structures: naphthalene (NP), fluorene (FL), and phenanthrene (PHE), on the HDS of dibenzothiophene over a sulfided NiMo/γ-Al2O3 catalyst. Kinetic modeling was based on the Langmuir–Hinshelwood–Hougen–Watson (LHHW) formalism and was submitted to regression analyses with the reparametrized form of the Arrhenius and van’t Hoff equations. Before addressing inhibition effects, the kinetics of the HDS of DBT was revisited. In this sense, observations were better fitted when considering that the two parallel pathways for the HDS of DBT, i.e., the so-calle...

Enhanced catalytic activity of monodispersed porous Al2O3 colloidal spheres with NiMo for simultaneous hydrodesulfurization and hydrogenation.

Novel composites made from monodispersed porous Al-glycolate spheres (NiMo/Al-SP) were synthesized through alcoholysis or hydrolysis treatments. The obtained samples were characterized by a complementary combination of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N2 physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR), and pyridine Fourier transform infrared spectroscopy (Py FT-IR). In addition, the catalytic performances of the resultant catalysts were evaluated in the simultaneous HDS of dibenzothiophene (DBT) and HYD of naphthalene (DBT and naphthalene represent the sulfur-containing compounds and polycyoalkanes, respectively). The experimental results showed that, 71.22% DBT and 88.28% naphthalene were converted by NiMo/Al-SP(H) under the conditions of 270 °C temperature, 5 MPa H2 (initial pressure at room temperature) and 10 h reaction time. The design and preparation of NiMo/Al-SP provide an effective and novel pathway for the development of high-performance catalysts and production processes.

Effects of Phosphorus Content on Simultaneous Ultradeep HDS and HDN Reactions over NiMoP/Alumina Catalysts

The effects of phosphorus content on competitive hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and hydrodenitrogenation (HDN) of quinoline (Q) over NiMo catalysts were evaluated. Reactions were carried out in a trickle-bed high-pressure flow microreactor. HDS of 4,6-DMDBT was strongly inhibited at Q concentrations of 90 ppmw N, mostly hydrogenation (HYD) route in HDS, suggesting that 4,6-DMDBT and Q compete for the same hydrogenation active sites, which was confirmed by the products’ distribution in HDN reactions. Morphology and nature of active sites promoted by phosphorus addition led to different activity performance on competitive HDS and HDN reactions, as evidenced by TOF values. At low concentrations of Q, promoted catalysts maintained activity for both HDS and HDN. High Q levels (above 90 ppmw N) decreased HDS and HDN activity due to stronger inhibition of catalysts. The addition of 1 wt % of phosphorus showed superior activity, attributed to a combination of better dispers...

XPS study of a bulk WP hydrodesulfurization catalyst

The X-ray photoelectron spectroscopy characterization of a bulk WP hydrodesulfurization (HDS) catalyst demonstrated that the actual active surface phase of WP in the HDS of dibenzothiophene (DBT) is a sulfur-containing phase. This tungsten phosphosulfide phase formed faster than the molybdenum phosphosulfide phase, but possessed a lower sulfur content than the corresponding Ni2P and MoP phases. NH3 was the dominant nitrogen-containing species detected in the WP catalyst after simultaneous HDS and hydrodenitrogenation reactions. NH3 decreased the DBT conversion strongly but less than piperidine, indicating that not only N-containing compounds but also NH3 inhibits the HDS activity of WP.

Synthesis of a Ti-SBA-15-NiMo Hydrodesulfurization Catalyst: The Effect of the Hydrothermal Synthesis Temperature of NiMo and Molybdenum Loading on the Catalytic Activity

We report herein the investigation of the catalytic activity on the hydrothermal synthesis temperature (HTsynT; 60–120 °C) and molybdenum loading (5–13 wt %) of NiMo catalyst supported over titanium-modified mesoporous silica (Ti-SBA-15) for the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4-methyldibenzothiophene (4-MDBT) in dodecane. It was found that the dispersion of an NiMo active phase in a one-pot synthesis is size-dependent and mostly controlled by the HTsynT for an efficient HDS catalytic performance. The as-developed catalysts were characterized by N2 physiosorption, X-ray diffraction (XRD), temperature-programmed techniques, and scanning electron microscopy. XRD analysis revealed that MoO3 particles agglomerate to form a high crystalline phase, as a function of the hydrothermal temperature and molybdenum loading, which, in turn, affects the textural properties, number of active sites, and reduction temperature. The catalytic performance for the simultaneous HDS of DBT a...

Effect of pH on Activity of NiMo/Al2O3 Catalysts Prepared with Citric Acid in Simultaneous Hydrodesulfurization and Hydrodenitrogenation Reactions

NiMo/alumina catalysts were prepared by impregnation of metal precursors in the presence of citric acid (CA) at different pHs. Catalysts were characterized by nitrogen physisorption, X-ray diffraction, temperature programmed reduction of sulfided catalysts (TPR-S), temperature programmed sulfidation (TPS) and NO chemisorption of sulfided catalysts. Catalytic activity for dibenzothiophene (DBT) hydrodesulfurization (HDS) was studied in a trickle-bed reactor, with and without quinoline in the reaction feed. Results suggest that HDS of DBT occurs mainly by direct desulfurization route and CA addition at pH 3 was detrimental, resulting in a less active catalyst, which was confirmed by TOF calculations. Furthermore, TPR-S results show that the catalyst prepared at pH 3 presented less coordinatively unsaturated sites (CUS), being less active than the one synthesized at pH 1. Besides that, the catalyst prepared at pH 1 was less inhibited at higher quinoline concentrations.

Development of new hydrodesulfurization NiMo catalysts supported on Al2O3-TiSBA-15 hybrid materials

In the present work, a series of NiMo catalysts supported on hybrid materials consisting of mesoporous TiSBA-15 and conventional γ-alumina were prepared. Three hybrid supports were synthesized with 20, 40 and 60wt.% of TiSBA-15 and compared to pure γ-Al2O3 and TiSBA-15 counterparts. NiMo catalysts were prepared by incipient wetness co-impregnation of aqueous solutions of ammonium heptamolybdate and nickel nitrate precursors. Supports and catalysts were characterized by N2 physisorption, XRD, UV–vis DRS, temperature programmed reduction (TPR) and ammonia TPD. The sulfided NiMo catalysts were characterized by HRTEM and evaluated in the simultaneous hydrodesulfurization of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). All NiMo catalysts supported on hybrid materials showed better dispersion of the catalytically active MoS2 phase than the reference catalyst supported on the conventional γ-alumina material. Their activity was similar to that of the NiMo/γ-Al2O3 catalyst in HDS of DBT, but substantially higher in HDS of 4,6-DMDBT.

Phenomenological kinetics modeling of simultaneous HDS of dibenzothiophene and substituted dibenzothiophene over CoMoP/Al2O3 catalysts

A series of CoMo/γ-Al2O3 catalysts modified with P2O5 were prepared. The phosphorus concentration varied from 0.0 to 1.0wt.% P2O5. The catalysts prepared were evaluated in a batch autoclave reactor to investigate the effect of P2O5 on the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4-methyl dibenzothiophene (4-MDBT). The phenomenological based kinetics models are developed based on the experimental conversion and selectivity data. The analysis of the developed model suggests that a Langmuir–Hinshelwood mechanism fits the experimental data adequately. The rate constants for the formation of BP are 6–8 times higher than the rate constants for the formation of CHB. Similarly, the rate constants for the formation of MBP are 3–5 times higher than the rate constants of MCHB formation. These observations indicate that the HDS of the model compounds through the DDS route is several times faster than the HDS through the HYD route. Furthermore, the rate constant for the formation of BP and CHB is about two times higher than the respective rate constant for the formation of MBP and MCHB. The addition of P2O5 favored the DDS pathway over the HYD pathway for both DBT and 4-MDBT.

HDS performance of NiMo catalysts supported on nanostructured materials containing titania

In the present work, NiMo catalysts supported on titania-containing materials of the SBA family (Ti-SBA-15 and Ti-SBA-16) and on titania nanotubes of different pore diameters were prepared with the aim of selecting the most promising catalysts for deep hydrodesulfurization (HDS) of gas oil. Supports and catalysts were characterized by nitrogen physisorption, XRD, temperature programmed reduction, ammonia TPD, UV–vis DRS and scanning electron microscopy (SEM-EDX). Sulfided catalysts were characterized by HRTEM and tested in the simultaneous HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). For comparison purposes, a conventional NiMo/γ-Al2O3 catalyst was used. In HDS of DBT, all catalysts supported on titania-containing nanostructured materials showed similar activity as the NiMo/γ-Al2O3 reference, but in HDS of 4,6-DMDBT their activities were about twice higher than that of NiMo/γ-Al2O3. Regarding selectivity, for DBT HDS, the presence of titania in the supports resulted in an increase in the proportion of CHB product, whereas for 4,6-DMDBT different behavior was observed. Thus, NiMo catalysts supported on Ti-SBA-15 and Ti-SBA-16 showed similar selectivity as the NiMo/γ-Al2O3. On the contrary, the catalysts supported on titania nanotubes allowed reaching high conversions of 4,6-DMDBT with a much lower proportion of hydrogenated products, which is an interesting result not observed by us previously.

Competitive HDS and HDN reactions over NiMoS/HMS-Al catalysts: Diminishing of the inhibition of HDS reaction by support modification with P

Individual and simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrodenitrogenation (HDN) of carbozole reactions have been studied in the presence of hydrogen (P=55bar) at 310°C in a batch reactor over a series of sulfided NiMo/P/Al-HMS catalysts modified with phosphorus (0.5–2.0wt%). Both oxidic precursors and sulfide catalysts have been characterized by specific surface area, XRD, Raman, TPD-NH3, HRTEM, XPS and IR spectroscopy of adsorbed pyridine. Regardless of the reaction studied, all P-containing catalysts showed higher activity than that to the P-free one. The catalyst modified with optimized amount of P (1wt%) the best HDS activity and exhibited a lowest inhibition factor during simultaneous HDS and HDN, which was close to that of a commercial NiMo/Al2O3 sulfide catalyst. This was linked with formation of irregular MoS2 structures having high concentration of brim sites as well as with its largest total acidity.

Development of improved catalysts for deep HDS of diesel fuels

Deep hydrodesulfurization (HDS) of gas oils continues to attract research interest due to environmental-driven regulations which limit its sulfur content to 10–15 ppm in several countries. This paper highlights some of the recent studies conducted at King Fahd University of Petroleum and Minerals to develop improved HDS catalysts. The first study was focused on the effect of Co/(Co + Mo) ratio in CoMo/Al2O3 catalysts on HDS pathways of benzothiophene (BT) and dibenzothiophene (DBT). Co/Co + Mo ratio exhibited significant influence on the direct desulfurization (DDS) pathway, but showed no influence on the hydrogenation pathway. A Co/Co + Mo ratio of 0.4 exhibited optimum promotion effect of Co for HDS by DDS route and hence overall HDS. The second study investigated the effect of phosphorus addition on simultaneous HDS reactions and their pathways. The results indicate that phosphorus modification of CoMo/γ-Al2O3 catalysts resulted in enhancement of HDS due to increased dispersion of MoO3 and the maximum enhancement was achieved with 1.0 wt % P2O5. Enhancement of HDS rates was in the following order: 4,6-DMDBT (51 %) > 4-MDBT (38 %) > DBT (26 %). In the third approach, a series of NiMo catalysts supported on Al2O3-ZrO2 composites containing 0–10 wt % ZrO2 was synthesized, characterized and evaluated for deep desulfurization of gas oil. An increase of 1.3–2.5 times increase in HDS activity at 320–360 °C was observed due to reduced interaction between Al2O3 and the active metals. A correlation was found between the enhancement of hydrogenation activity of sulfided catalysts and the reducibility of their oxide precursors.