Catalytic Activity For Hydrodesulfurization Research Articles

Suppression of inactive sites in NiMo@amorphous alumina catalysts for hydrodesulfurization reaction: Effect of Ga doping

Hydrodesulfurization (HDS) reaction activity depends on the formation of active NiMoS (completely sulfided multilayer type 2 sites) and inactive NiAl2O4/NixSy phases on the catalyst surface. These inactive phases not only itself inactive for the reaction but also hinder the formation of active NiMoS phases. In addition, the formation of strong Mo-O-Al bonds also lowers the reducibility of the catalyst, suggesting lesser catalytic activity (type 1 sites, partially sulfided single-layer sites). To this end, we report the formation of NiMo/Ga doped amorphous alumina (A-Al2O3) catalysts prepared by the colloidal synthesis method. A-Al2O3 was chosen as a support because it has lower surface energy, better physicochemical properties, and enhanced acidic sites than the crystalline alumina phase, which favours the formation of type 2 sites or weak metal-support interaction (completely sulfided multilayer NiMoS sites). Further, the Ga doping in A-Al2O3 support substitute the tetrahedral Al sites and form GaAl2O4 phases by reducing NiAl2O4 inactive sites, and the free Ni decorate the edges of MoS2 to form HDS active NiMoS sites. Therefore, NiMo/Ga doped A-Al2O3 catalyst (at 1 wt% Ga loading) reported enhanced HDS catalytic activity (25%), HDS reaction rate constant (kHDS-2.15 times) and turn over frequency (TOF-1.3 times) than the conventional NiMo/γ-Al2O3 catalysts.

Testing conditions for CoMo HDS catalyst in the kinetic region: integrated approach using the math calculations and catalytic experiments

The main idea of the investigation was to define testing parameters with the lowest influence of internal and external diffusion on catalytic activity in hydrodesulfurization of dibenzothiophene. Traditional experimental methods were used to determine the conditions for the influence of internal and external diffusion. Simultaneous change of a linear feedstock rate and a catalyst loading at constant weight hour space velocity were used to determine the process temperature (240–260 °C) at which the impact of external diffusion is minimal. Catalytic tests, including the variation of the catalyst fraction size, were carried out to define the conditions with the lowest influence of internal diffusion. It was found that when the catalyst with the fraction size of 0.1–0.25 mm was used, the fluctuation of sulfur conversion was the smallest. Besides, to validate experimental results, the calculations were performed with mass balance equations and expressions used for HDS modeling. The resulting data and catalytic experiments demonstrated that the lowest influence of internal and external diffusion is achieved at a temperature process less than 260 °C and a catalyst fraction of 0.1–0.25 mm.

Effect of Adding Chelating Ligands on the Catalytic Performance of Rh-Promoted MoS2 in the Hydrodesulfurization of Dibenzothiophene

Hydrodesulfurization (HDS) is a widely used process currently employed in petroleum refineries to eliminate organosulfur compounds in fuels. The current hydrotreating process struggles to remove organosulfur compounds with a steric hindrance due to the electronic nature of the current catalysts employed. In this work, the effects of adding chelating ligands such as ethylenediaminetetraacetic acid (EDTA), citric acid (CA) and acetic acid (AA) to rhodium (Rh) and active molybdenum (Mo) species for dibenzothiophene (DBT) HDS catalytic activity was evaluated. HDS activities followed the order of RhMo/ɣ-Al2O3 (88%) > RhMo-AA/ɣ-Al2O3 (73%) > RhMo-CA/ɣ-Al2O3 (72%) > RhMo-EDTA/ɣ-Al2O3 (68%). The observed trend was attributed to the different chelating ligands with varying electronic properties, thus influencing the metal–support interaction and the favorable reduction of the Mo species. RhMo/ɣ-Al2O3 offered the highest HDS activity due to its (i) lower metal–support interaction energy, as observed from the RhMo/ɣ-Al2O3 band gap of 3.779 eV and the slight shift toward the lower BE of Mo 3d, (ii) increased Mo-O-Mo species (NMo-O-Mo ~1.975) and (iii) better sulfidation of Rh and MoO in RhMo/ɣ-Al2O3 compared to the chelated catalysts. The obtained data provides that HDS catalytic activity was mainly driven by the structural nature of the RhMo-based catalyst, which influences the formation of more active sites that can enhance the HDS activity.

Preparation of Ni2P Decorated Black Phosphorus Nanosheets Supported on Two‐Dimensional α‐Zirconium Phosphate and Its Catalysis for Hydrodesulfurization of Dibenzothiophene

AbstractIn this paper, a novel Ni2P/black phosphorus (Ni2P/BP) supported on two‐dimensional α‐zirconium phosphate (α‐ZrP) hybrid material was prepared, and its catalytic activity for hydrodesulfurization (HDS) was investigated. Through the reaction of nickel salt with BP nanosheets obtained by freeze‐assisted exfoliation method, Ni2P nanoparticles can be formed and firmly anchored on the surface of BP, effectively preventing themselves from aggregating. BP is not only used as the phosphorus source for the synthesis of Ni2P, but its superior electron mobility can significantly promote the catalytic HDS activity of Ni2P species. Moreover, the support of two‐dimensional α‐ZrP nanosheets with a large specific surface area has a strong structure, which greatly improves the stability of catalyst. The Ni2P/BP@ZrP catalyst could reach a dibenzothiophene (DBT) conversion of 87.4 % within 6 h at 260 °C, much higher than the traditional NiMo/Al2O3 catalyst (65.6 %), showing a promising application for industrial catalytic desulfurization.

Is it possible to reactivate hydrotreating catalyst poisoned by silicon?

The feasibility of the reactivation of CoMo/Al2O3 hydrotreating catalysts poisoned by Si compounds has been studied. CoMo/Al2O3 catalysts poisoned with 3, 4 and 5 wt.% of silicon were obtained during hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane. Catalysts poisoned by different amount of silicon were regenerated by oxidative treatment and subsequently reactivated using citric acid solution. The catalysts were studied by nitrogen adsorption-desorption method, CHNS analysis, UV–vis, thermal analysis, SEM, HRTEM, XPS. It was shown that the hydrodesulfurization activity of regenerated catalysts decreased with increasing silicon content. According to UV–vis results, the increase in Si content on the spent catalyst leads to the formation of CoOx oxides after oxidative regeneration. Probably, cobalt oxides do not promote MoS2 slabs during sulfidation, convert to inactive Co species and decrease hydrodesulfurization activity. After reactivation procedure, there was the increase in active component particles dispersion, while catalytic activity in hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline increased. It was established that hydrodesulfurization and hydrodenitrogenation activities of CoMo/Al2O3 catalyst with less than 3 wt.% of Si could be completely restored by reactivation.

Solvothermal synthesis of three-dimensional molybdenum and rhenium diselenides and their performance in the hydrodesulfurization of dibenzothiophene

Molybdenum and rhenium selenides hierarchical structures consisting of self-assembled few-layered stacked nanosheets were synthesized via a solvothermal route, by reacting rhenium and molybdenum carbonyls, selenium powder, and p-xylene as solvent. Both materials were evaluated and compared in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The characterization techniques revealed different morphologies for both diselenides: MoSe2 has a flowerlike microstructure composed of few-layered stacked nanosheets, while ReSe2 shows a microspherical structure with smaller and randomly oriented few-layered stacked nanosheets. The HDS catalytic activity displayed by ReSe2 was more than twice than that obtained for MoSe2, with a clear preference for the direct desulfurization (DDS) path.

Ultrasmall Ni-Promoted WS2 Nanocatalyst with Enhanced Number of Edge Atoms for Hydrodesulfurization

Ni-promoted WS2 catalysts are preferred over Ni/Co promoted MoS2 catalysts due to their enhanced HDS catalytic capability towards methylated dibenzothiophene compounds. However, it is challenging to prepare the active Ni-promoted WS2 phase with optimal number of edge/brim sites because WO3 and NiO have different sulfidation temperatures, which favors the formation of non-promoted WS2 and NiSx phase instead of active NiWS phase. Herein, we report a versatile method to prepare ultrasmall Ni promoted WO3 nanoclusters (~ 3 nm) supported over γ-Al2O3 followed by sulfidation. The prepared nanocatalysts possess increased hydrodesulfurization catalytic activity towards dibenzothiophene (conversion for the best catalyst was 92% at 580K) and 4,6 dimethyl dibenzothiophene (conversion for the best catalyst was 57% at 580K) compared to the conventional wet impregnated catalyst possessing similar chemical composition. The increased catalytic activity is attributed to easier reducibility (confirmed by temperature progra...

Effect of pre-activation treatment temperature on hydrodesulfurization catalytic activity of CoMoS/KIT-6

Mesoporous silica-supported cobalt–molybdenum hydrodesulfurization catalysts have been prepared by wetness impregnation, drying and a thermal pre-treatment of impregnated support before activation. Characterization of materials was made by nitrogen adsorption, thermogravimetric analysis, Raman spectroscopy, TEM and XPS. Catalytic activity was determined by hydrodesulfurization of dibenzothiophene (DBT). The results indicate that the thermal pre-treatment carried out at the lower temperature allows the formation of smaller and less stacked active phase structures, with a higher amount of CoMoS phase.

Promotional effect of Ga for Ni2P catalyst on hydrodesulfurization of 4,6-DMDBT

Ni2P catalysts supported on SiO2 and Ga-SiO2 were prepared by incipient wetness impregnation technique, and the effect of the electronic properties of Ni2P on hydrodesulfurization (HDS) performance was studied. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and in situ FT-IR with CO adsorption studies were used to examine structural and electronic properties of the supported Ni2P catalysts. The catalytic activity in hydrodesulfurization (HDS) was measured at 3.0 MPa and at three different temperatures of 613, 628, and 643 K in a three-phase fixed bed reactor using a model feed containing 500 ppm S as 4,6-DMDBT, 6000 ppm S as DMDS, 100 ppm N as quinoline, 1 wt% tetralin, and 0.5 wt% n-nonane in n-tridecane balance. In both cases, the HDS conversion was very high over 90%. For the product distributions, the Ni2P/SiO2 maintained a low direct desulfurization (DDS) selectivity at 26.5%, while the Ni2P/Ga-SiO2 exhibited higher DDS selectivity of 32.1% at 643 K. The Ni K-edge XANES and CO-adsorbed FT-IR analysis confirmed the electron enriched property of Ni2P on SiO2, but with the electron deficiency of Ni2P phase supported on Ga-SiO2 support. These results thus suggest that the electron deficient Ni2P favors σ-bonding with S compounds to promote direct desulfurization of 4.6-DMDBT.

Cobalt-Molybdenum Single-Layered Nanocatalysts Decorated on Carbon Nanotubes and the Influence of Preparation Conditions on Their Hydrodesulfurization Catalytic Activity

Hydrodesulfurization (HDS) of crude oil plays a vital role in the refining of petroleum products. With ever-increasing regulations restricting the allowable concentrations of sulfur in fuel, further research is required to produce more efficient and effective catalysts. Herein, we have synthesized carbon nanotube (CNT)-supported cobalt-molybdenum (CoMo) catalysts for HDS of dibenzothiophene (DBT) via Co-first and Mo-first sequential impregnation as well as co-impregnation. Spectroscopic analysis shows the formation of a CoMo catalyst with no free sulfided Co phase present. Additionally, CoMo catalysts are found to be predominantly single-layered nanocatalysts layered on the CNT support. Temperature-programmed reduction (TPR) measurements show differences in reducing temperature of the sulfided CoMo catalysts prepared by the different methods, but catalyst activities for HDS of DBT did not fully align with the TPR-predicted order. Thus, provided the reaction temperature is high enough, reducibility may not...

Ni2P/ZrO2-SBA-15 Dibenzothiophene Hydrodesulfurization Catalysts: Preparation, Characterization and Evaluation

Ni2P/ZrO2-SBA-15 catalysts with different zirconium n-propoxide/SBA-15 mass ratios were synthesized to evaluate their dibenzothiophene hydrodesulfurization catalytic activity. Effect of ZrO2 introduction was investigated. Supports and catalysts were characterized by BET, XRD, 29Si NMR, XPS and FTIR. The results indicated that zirconium was incorporated into SBA-15 in the forms of [(–O–)2Si(–O–Zr)2] and/or [(–O–)3Si–O–Zr], and that the SBA-15 framework structure was maintained after incorporation of ZrO2. With zirconium content increasing, ZrO2 was transformed from amorphous phase to tetragonal phase. Zirconium incorporation into SBA-15 supports could facilitate to form more dispersed Ni2P active phase. There might be some interaction occurring between the P and Zr species. In addition to Ni2P, another kind of active phase, ZrP, was formed, which might exhibit a better HDS activity than Ni2P. It was observed that at a temperature of 280 °C, pressure of 3.0 MPa, WHSV of 6.5 h−1 and H2 to oil ratio of 450, the Ni2P/Zr-SBA(1.5) catalyst, where 1.5 represents zirconium n-propoxide/SBA-15 mass ratio, showed the highest DBT conversion, which was 86.6%, almost 35% higher than that of the Ni2P/Zr-SBA(0) catalyst.

Sulfur resistant nature of Ni2P catalyst in deep hydrodesulfurization

Catalysts consisting of Ni2P placed on low and high surface area siliceous supports, i.e. SiO2-L, SiO2-H, and Si-MCM-41, were synthesized by TPR (temperature-programmed reduction), and the effect of the sulfur and nitrogen content of the feed on hydrotreating activity was studied. Structural information on the supported Ni2P phase after reaction was obtained by XRD (X-ray diffraction) and EXAFS (extended X-ray absorption fine structure) measurements. The catalytic activity in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) was obtained at 573 and 613K and a pressure of 3.1MPa in an upflow, liquid-gas-solid bed reactor with a feed consisting of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and quinoline dissolved in tridecane as solvent. Using reference compositions of 4,6-DMDBT at levels of 500ppm S, dimethyldisulfide (DMDS) at levels of 6000ppm S, and quinoline at levels of 200ppmN, the order of activity was Ni2P/SiO2-L<Ni2P/SiO2-H<Ni2P/MCM-41, compared on the basis of equal number of sites (230mmol) placed in the reactor. The Ni2P/MCM-41 gave a notably high conversion in HDS of 98% that was substantially above those of a Ni-Mo-S/Al2O3 commercial catalyst which had an HDS conversion of 81%, on a basis of equal quantity of sites (230mmol) placed in the reactor. The sites were titrated by pulse CO uptakes for the phosphides and by pulse O2 adsorption at low temperature for the sulfide. Analysis of the spent samples by EXAFS showed that Ni(2) sites of square pyramidal geometry in Ni2P are bound to sulfur, with a lower NiS coordination, as the particle size decreased, and the order in the number of these sites followed the reactivity Ni2P/SiO2-L<Ni2P/SiO2-H<Ni2P/MCM-41. It is thus concluded that the active Ni(2) site on the highly dispersed Ni2P is much more tolerant to sulfur than the tetrahedral Ni(1) sites also present in the samples.

Insight into thiophene hydrodesulfurization on clean and S-modified MoP(010): a periodic density functional theory study.

The hydrodesulfurization (HDS) of thiophene on clean and S-modified MoP(010) is investigated to understand the HDS mechanism as well as the surface sulfur (S) atom effect using periodic density functional theory (DFT). The results show that thiophene prefers strongly flat adsorption on both the clean and S-modified surfaces, in either the molecular state or the dissociative state breaking simultaneously one C-S bond, and the adsorption of thiophene can be slightly weakened by the surface S atom. Thermodynamic and kinetic analysis indicates that the HDS of thiophene in both the molecular and dissociative adsorption states prefers to take place along the direct desulfurization (DDS) pathway rather than hydrogenation on both the clean and S-modified MoP(010) surfaces. Surface S shows a promotion effect on the HDS catalytic activity of MoP(010), because the energy barrier/rate constant of the rate-determining step on the DDS pathway is decreased/enlarged under the S modification. Compared with the situation of MoP(001), MoP(010) should have relatively low HDS activity, since a higher energy barrier as well as weaker exothermicity is involved in the reaction on the latter surface.

Formation of Rh&lt;sub&gt;2&lt;/sub&gt;P Supported on Na-form Zeolites and Catalytic Activity for Hydrodesulfurization

Formation of Rh&lt;sub&gt;2&lt;/sub&gt;P Supported on Na-form Zeolites and Catalytic Activity for Hydrodesulfurization

The hydroxyapatite nanotube as a promoter to optimize the HDS reaction of NiMo/TiO2 catalyst

A composite containing TiO2 whiskers (TiO2(w)) and hydroxyapatite nanotube (nHA) with mosaic structure functioned as a support was successfully synthesized by a facile route. The TiO2(w) was prepared from potassium titanate and the novel single-crystalline hydroxyapatite nanotubes were synthesized via a distinctive biomimetic route. Properties of support and catalyst were characterized by SEM, TEM, XRD, FT-IR of adsorbed pyridine (in situ FT-IR), BET, TPR, and NH3-TPD. Catalytic activity of NiMo/TiO2(w)-nHA, and the effect of nHA contents on hydrodesulfurization (HDS) activity was performed. Results indicated the incorporation of nHA can weaken the Lewis acidity of TiO2 supports and decrease acidity of the NiMo/TiO2(w)-nHA catalyst. The addition of moderate nHA has weak influence on the textural and structural properties of the catalyst. NiMo/TiO2(w)-nHA exhibits higher HDS catalytic activity than that of NiMo/TiO2(w) catalyst under mild conditions of low temperature and pressure (280°C and 2MPa), and the catalytic performance of NiMo/TiO2(w)-nHA-0.1 is the best. The synergistic effects between TiO2(w) and nHA and acidity regulation contribute to improve the HDS catalytic activity of the nHA-doped samples.

Surface Carbon Activated NiMo/TiO2 Catalyst Towards Highly Efficient Hydrodesulfurization Reaction

By adopting molecular self-assembly, the surface of mesoporous TiO2 whiskers (TiO2(w)) was modified with 18 alkyl phosphate as carbon source. This method was successfully used to form a carbon heterogeneous monolayer on titania surface (TiO2(w)–C) under N2 atmosphere. Novel NiMo/TiO2(w)–C catalysts were prepared by incipient-wetness impregnation. The carriers and catalysts were characterized by N2 adsorption–desorption measurements, NH3-temperature-programmed desorption, Raman Spectra, Fourier transform infrared, scanning electron microscopy, temperature-programmed reduction, and H2S-temperature-programmed desorption. The catalytic activity of TiO2(w)–C as a support, together with the effect of carbon content on hydrodesulfurization (HDS) activity of NiMo/TiO2(w)–C was investigated. The results showed that NiMo/TiO2(w)–C exhibited higher HDS catalytic activity under conditions of low temperature and pressure (280 °C and 2 MPa). Under such mild reaction conditions, NiMo/TiO2(w)–C-0.5 with carbon loading of 0.5 % showed the highest HDS result (100 %). The improved activity of NiMo/TiO2(w)–C-0.5 can be attributed to the TiO2(w) modifying with trace amounts of carbon, which would increase the total acid sites and suppress the carbon deposition on the surface of catalyst. Additionally, the generated carbon nanoparticles can weaken the interaction between TiO2(w) and the HDS product (H2S) and then improve H2S desorption from the catalyst surface, which lead to the outstanding HDS activity.

Effect of the Reduction Temperature on Nickel Phosphide Catalyst Structure and Catalytic Activity for Hydrodesulfurization

Ni2P/TiO2-Al2O3 catalysts were prepared by impregnation of nickel phosphate precursors followed by reduction in hydrogen. The catalysts were characterized by X-ray diffraction (XRD), N2-adsorption specific surface area measurements (BET), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetry differential thermal analysis (TG-DTA). The effects of reduction temperature on catalyst structure and HDS activity were studied using a lab-scale continuous flow fixed-bed reactor.. The results indicated that the catalyst prepared with reduction temperature of 973 K exhibited the best performance. At a reaction temperature of 606 K, a pressure of 3.0 MPa, a hydrogen/oil ratio of 500 (V/V), and a weight hourly space velocity (WHSV) of 2.0 h-1, the conversion of DBT HDS was 96.0%.

Sulfidability and thiophene hydrodesulfurization activity of supported NiMo carbides

Ni–Mo carbides supported on activated carbon were synthesized by carbothermal hydrogen reduction and the effect of the sulfidability on the thiophene hydrodesulfurization catalytic activity was studied. The X-ray diffraction patterns of Ni–Mo carbides showed the presence of β-Mo2C and NiC when the atomic ratio AR=Ni/(Ni+Mo) was between 0.25 and 0.75, while for AR=1, it only was detected metallic Ni. The X-ray photoelectron spectroscopy results showed the distribution of different surface species in the passivated catalysts: Moδ+ (0≤δ≤2), Mo4+, Mo6+, Niδ+ and Ni2+. After sulfiding the carbides were modified in their surface and catalytic activity.

Effect of titanium content on dibenzothiophene HDS performance over Ni2P/Ti-MCM-41 catalyst

Ni2P/Ti-MCM-41 catalysts were successfully prepared under a lower reduction temperature of 400°C, and the effects of Ti on the catalytic properties for hydrodesulfurization (HDS) were investigated. The prepared catalysts were characterized by X-ray diffraction, N2-adsorption specific surface area measurements, Fourier transform infrared spectroscopy of adsorbed pyridine, X-ray photoelectron spectroscopy, transmission electron microscope (TEM) and CO uptake. The incorporation of Ti can enhance the Lewis acidity and the Brönsted acidity of MCM-41 supports and induce proper Lewis acidity of the Ni2P/Ti-MCM-41 catalyst. An appropriate amount of Ti can promote the formation of the Ni2P phase and induce a better Ni2P dispersion. The catalyst prepared with a Ti/Si molar ratio of 1.5% exhibited the highest HDS activity of 99.4%. The Ti electronic effect (through the direct desulfurization route) and the moderate surface Lewis acidity (through the hydrogenation route) may explain the improved HDS catalytic activity of the Ti-doped samples.

Relationship between active phase morphology and catalytic properties of the carbon–alumina-supported Co(Ni)Mo catalysts in HDS and HYD reactions

Effects of activated carbon of a carbon-coated alumina support and active phase morphology of transition metal sulfide (TMS) catalysts in hydrotreatment (HDT) of S-containing compounds were studied. The catalysts were synthesized from Anderson-type heteropoly compounds and characterized with multiple methods: X-ray powder diffraction, N2 physisorption, temperature-programmed desorption of ammonia, pyridine-adsorbed Fourier transform infrared spectroscopy, H2 temperature-programmed reduction, and high-resolution transmission electron microscopy. The catalysts were tested in hydrodesulfurization (HDS) of thiophene, dibenzothiophene and HDT of diesel. The results suggest that the catalytic activity in HDS and hydrogenation reactions depends on the shape of crystallites of the active phase. The results are interpreted using recently proposed concept of interlayer dynamics. This concept is helpful in establishing structure–activity relations for TMS.