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.     

Effect of pore size on bitumen hydrocracking over Al2O3-AlPO4 supported Ni-Mo catalysts

A study of co-precipitated aluminum oxide-aluminum phosphate (AAP) materials as supports of Ni-Mo heavy oil upgrading catalysts has been completed. Results of both short duration (8 h) and longer duration (up to 200 h) experiments at conditions relevant to the commercial H-Oil process are reported and compared with a commercial NiMo/Al₂O₃ catalyst. The initial activity of the Ni-Mo/AAP catalysts correlates with the catalyst average pore diameter which is determined by the P content of the AAP support. An optimum pore diameter of about 20 run exists for HDM whereas for HDS a pore diameter < 10 nm is desirable. After 100 h operation the HDM conversion of the best Ni-Mo/AAP catalyst was approximately 10 percentage points greater than for the commercial catalyst. The HDS and CCR conversions were comparable over the two catalysts. The difference in performance between the catalysts is attributed primarily to the smaller pore size of the Al₂O₃ support compared to the AAP support. The amount of coke deposited on the Ni-Mo/AAP catalyst was less than that on the commercial catalyst, presumably due to differences in pitch conversion levels.     

Preparation,characterization and hydrotreating performances of ZrO2–Al2O3-supported NiMo catalysts

A series of Al₂O₃–ZrO₂ composite supported NiMo catalysts with various ZrO₂ contents were prepared. Several techniques including XRD, SEM, N₂ physisorption, H₂-TPR, and UV–vis DRS were used for typical physico-chemical properties characterization of the ZrO₂–Al₂O₃ composite supports and their NiMo/ZrO₂–Al₂O₃ catalysts. The test results showed that the composite supports prepared by the chemical precipitation method existed as amorphous phase in the samples with insufficient contents of ZrO₂, and the incorporation of ZrO₂ into supports provided a better dispersion of NiMo species, which made their reductions become easier. The pyridine-adsorbed FT-IR results indicated that the Lewis acid sites of catalysts increased significantly by the introduction of ZrO₂ into the supports. The activities of these catalysts for diesel oil hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high pressure micro-reactor system. The results showed that the ZrO₂–Al₂O₃-supported NiMo catalysts with suitable ZrO₂ contents exhibited much higher catalytic activities than that of Al₂O₃-supported one, and when the ZrO₂ contents were 15% and 5%, the NiMo/Al₂O₃–ZrO₂ catalysts presented the highest HDS and HDN activities, respectively.     

Effect of catalyst composition on the hydrodesulphurization and hydrodemetallization of atmospheric residual oil

A series of CoMo/Al₂O₃ catalysts containing a third additive, a Si, Ti, or P compound, were prepared using a consecutive impregnation method. The activities for the hydrodesulphurization (HDS), hydrodemetallization (HDM) and Conradson carbon residue (CCR) reduction of atmospheric residual oil were tested in a semi-batch basket type reactor. Cycle-aging tests were carried out for comparison of catalyst stability. The intrinsic rate constants of HDS from a semi-empirical calculation were used to test the coke tolerance of the catalysts. The CoMo/Al₂O₃ catalyst with a titanium compound added exhibited the highest activity enhancement for HDS and HDM reactions. It was also found that the surface activity maintenance can be effectively improved by the addition of an appropriate amount of titanium compound. The activity and stability of CoMo and NiMo catalysts for the HDS and HDM reactions were also compared.     

Nanosized HY zeolite-alumina composite support for hydrodesulfurization of FCC diesel

A series of hydrodesulfurization (HDS) NiMo catalysts supported on Al₂O₃-NY (denoted as ANY) composites with various amounts of nanosized H-type Y zeolite (denoted as NY) were prepared. The samples were characterized by XRD, BET, TPD, TPR, HRTEM, and FT-IR spectroscopy of pyridine adsorption. The characterization results showed that, compared with NiMo/Al₂O₃, the addition of NY reduced the Metal-support interaction and made the MoS₂ stacking degree higher, slabs shorter and dispersion of edge and corner Mo atoms bigger. The addition of NY also enhanced the overall acidity and the ratio of Brönsted acid to Lewis acid of these catalysts. The fluidized catalytic cracking (FCC) diesel HDS activity was increased with the addition of NY in these catalysts compared with NiMo/Al₂O₃ catalysts. The optimal NY content was found to be 20 wt% in ANY composite support. The highest HDS activity of NiMo/ANY20 was attributed to the synergy of hydrogenation activity, acid amount and textural properties.     

The role of nickel in pyridine hydrodenitrogenation over NiMo/Al2O3

Al₂O₃ supported Mo, Ni, and NiMo/Al₂O₃ catalysts with various Ni contents were prepared to investigate the role of Ni as a promoter in a NiMo bimetallic catalyst system. The hydrodenitrogenation (HDN) reaction of pyridine as a catalytic probe was conducted over these catalysts under the same reaction conditions and the catalysts were characterized using BET surface area measurement, infrared spectroscopy, temperature programmed reduction, DRS and ESR. According to the results of reaction experiments, the NiMo/Al₂O₃ catalyst showed higher activity than Mo/Al₂O₃ catalyst in the HDN reaction and particularly the one with atomic ratio [Ni/(Ni+Mo)]=0.3 showed the best activity for the HDN of pyridine. The findings of this study lead us to suggest that the enhancement in the HDN activity with nickel addition could be attributed to the improvement in the reducibility of molybdenum and the formation of Ni-Mo-O phase.     

Experimental and Kinetics Studies of Aromatic Hydrogenation in a Two‐Stage Hydrotreating Process using NiMo/Al2O3 and NiW/Al2O3 Catalysts

In this work, hydrogenation of aromatic compounds in light gas oil derived from Athabasca bitumen was carried out using a single‐ and two‐stage hydrotreating processes. Experiments were performed in a trickle‐bed reactor using two catalysts namely NiMo/Al₂O₃ and NiW/Al₂O₃. NiMo/Al₂O₃ was used in the first stage for nitrogen and sulphur containing heteroatoms removal whereas NiW/Al₂O₃ was used in the second stage for saturation of the aromatic rings in the hydrocarbon species. Temperature and liquid hourly space velocity (LHSV) were varied from 350‐390°C and 1.0‐1.5 h^?1, respectively, while pressure was maintained constant at 11.0 MPa for all experiments. Results from single‐stage were compared with those from two‐stage process on the basis of reaction time. Kinetic analysis of the single‐stage hydrotreating process showed that HDA and HDS activities were retarded by the presence of hydrogen sulphide that is produced as a by‐product of the HDS process. However, with inter‐stage removal of hydrogen sulphide in the two‐stage process, significant improvement of the HDA and HDS activities were observed.     

A comparative study on the effect of promoter content of hydrodesulfurization catalysts at different evaluation scales

CoMo and NiMo supported Al₂O₃ catalysts have been investigated for hydrotreating of model molecule as well as industrial feedstock. Activity studies were carried out for thiophene and SRGO hydrodesulfurization (HDS) in an atmospheric pressure and batch reactor respectively. These activities on sulfided catalysts were evaluated as a function of promoter content [M/(M + Mo) = 0.30, 0.34, 0.39; M = Co or Ni] using fixed (ca. 8 wt.%) molybdenum content. The promoted catalysts were characterized by textural properties, XRD, and temperature programmed reduction (TPR). TPR spectra of the Co and Ni promoter catalysts showed that Ni promotes the easy reduction of Mo species compared with Co. With the variation of promoter content NiMo catalyst was found to be superior to CoMo catalyst for gas oil HDS, while at low-promoter content the opposite trend was observed for HDS of thiophene. The behavior was attributed to the several reaction mechanisms involved for gas oil HDS. A nice relationship was obtained for hydrodesulfurized gas oil refractive index (RI) and aromatic content, which corresponds to the Ni hydrogenation property.     

Modification of the alumina‐supported Mo‐based hydrodesulfurization catalysts by tungsten

The incorporation effect of tungsten as an activity‐promotional modifier into the Ni‐promoted Mo/γ‐Al₂O₃ catalyst was studied. Series of W‐incorporated catalysts with different content of tungsten were prepared by changing the impregnation order of nickel and tungsten onto a base Mo/γ‐Al₂O₃. Catalytic activities were measured from the atmospheric reactions of thiophene hydrodesulfurization (HDS) and ethylene hydrogenation (HYD). The HDS and HYD activities of the WMo/γ‐Al₂O₃ catalysts (WM series) initially increased and subsequently decreased with increasing content of tungsten as compared with those of their base Mo/γ‐Al₂O₃. The maximal activity promotion occurred at the W/(W + Mo) atomic ratio 0.025. For the Ni‐promoted Mo/γ‐Al₂O₃ catalysts, the effect of W incorporation was greatly dependent on the impregnation order of tungsten. The catalysts prepared by impregnating Ni onto the WMo/γ‐Al₂O₃ catalysts showed the same trend of activity promotion as for the WM series, while those by impregnating W onto a NiMo/γ‐Al₂O₃ catalyst resulted in lower activities than their base NiMo/γ‐Al₂O₃ catalyst. To characterize the catalysts, temperature‐programmed reduction and low‐temperature oxygen chemisorption were conducted. The effects of W incorporation on the NiMo‐based catalysts were discussed in reference to those on the CoMo‐based catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydroprocessing of straight run diesel mixed with light cycle oil from fluid catalytic cracking,using sulfide NiMo catalyst on zeolite-containing supports

It is proposed that the sulfide NiMo system supported on alumina-SAPO-31 composite (NiMo/Al₂O₃-SAP catalyst) be used to obtain high-quality diesel fuel from a mixture of straight run diesel (SRGO) and light cycle oil (LCO) produced by fluid catalytic cracking (FCC). It is shown that the use of this catalyst ensures the synthesis of diesel fuel of higher quality upon hydroprocessing a feedstock with 30 wt % LCO, compared to the traditional sulfide NiMo/Al₂O₃ or CoMo/Al₂O₃ catalysts. It is found that the content of aliphatic hydrocarbons is raised in the products of hydrotreatment, compared to the initial feedstock. This confirms the ability of NiMo/Al₂O₃-SAP catalyst to facilitate the reaction of ring opening. Using the proposed catalyst should improve the quality of diesel fuels obtained via the hydroprocessing of LCO-containing feedstock.     

Mesoporous silica–alumina as support for Pt and Pt–Mo sulfide catalysts: Effect of Pt loading on activity and selectivity in HDS and HDN of model compounds

The potential of mesoporous silica–alumina (MSA) material as support for the preparation of sulfided Pt and Pt–Mo catalysts of varying Pt loadings was studied. The catalysts were characterized by their texture, hydrogen adsorption, transmission electron microscopy, temperature programmed reduction (TPR) and by activity in simultaneous hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine. Sulfided Pt/MSA catalysts with 1.3 and 2 wt.% Pt showed almost the same HDS and higher HDN activities per weight amounts as conventional CoMo and NiMo/Al₂O₃, respectively. The addition of Pt to sulfided Mo/MSA led to promotion in HDS and HDN with an optimal promoter content close to 0.5 wt.%. The results of TPR showed strong positive effect of Pt on reducibility of the MoS₂ phase which obviously reflects in higher activity of the promoted catalysts. The activity of the MSA-supported Pt–Mo catalyst containing 0.5 wt.% Pt was significantly higher than the activity of alumina-supported Pt–Mo catalyst. Generally, Pt–Mo/MSA catalysts promoted by 0.3–2.3 wt.% Pt showed lower HDS and much higher HDN activities as compared to weight amounts of CoMo and NiMo/Al₂O₃. It is proposed that thiophene HDS and pyridine hydrogenation proceed over Pt/MSA and the majority of Pt–Mo/MSA catalysts on the same type of catalytic sites, which are associated with sulfided Pt and MoS₂ phases. On the contrary, piperidine hydrogenolysis takes place on different sites, most likely on metallic Pt fraction or sites created by abstraction of sulfur from MoS₂ in the presence of Pt.     

Kinetics of Bitumen‐Derived Gas Oil Upgrading Using a Commercial NiMo/Al2O3 Catalyst

Hydrotreating (HT) kinetics of Athabasca bitumen‐derived gas oil has been studied between 340 to 420°C using a commercial NiMo/γ‐Al₂O₃ catalyst. The kinetics analyses included overall conversion of high‐boiling species into low‐boiling products, hydrodenitrogenation (HDN) of total, basic and non‐basic nitrogen compounds and hydrodesulfurization (HDS). Three temperature regimes were marked out for the kinetic analyses: low (340‐370°C), intermediate (370‐400°C) and high (400‐420°C). The mechanism for the conversion of high to low‐boiling species was observed to change from one temperature regime to the other, giving rise to different activation energies. HDS and HDN activation energies increased in the order: high < low < intermediate severity temperature regime.     

Mechanisms of hydrodenitrogenation of alkylamines and hydrodesulfurization of alkanethiols on NiMo/Al2O3, CoMo/Al2O3, and Mo/Al2O3

The simultaneous hydrodenitrogenation (HDN) of alkylamines and hydrodesulfurization (HDS) of alkanethiols, with the NH₂ and SH groups attached to primary, secondary, and tertiary carbon atoms, were studied at 270–320 °C and 3 MPa over sulfided NiMo/Al₂O₃, CoMo/Al₂O₃, and Mo/Al₂O₃ catalysts. Pentylamine and 2-hexylamine reacted by substitution with H₂S to form alkanethiols and with another amine molecule to form dialkylamines. Alkenes and alkanes were not formed directly from pentylamine and 2-hexylamine, but indirectly by elimination and hydrogenolysis of the alkanethiol intermediates, as confirmed by their secondary behavior and the similar alkene/alkane ratios in the simultaneous reactions of amines and thiols. Only 2-methyl-2-butylamine, with the NH₂ group attached to a tertiary carbon atom, produced alkenes as primary products by E1 elimination. NiMo/Al₂O₃ and CoMo/Al₂O₃ have a higher activity for the HDS of alkanethiols than does Mo/Al₂O₃; H₂S has a negative influence. This shows that the thiols react on vacancies on the catalyst surface (Lewis acid sites). Mo/Al₂O₃ is the best HDN catalyst; H₂S has a positive influence on the HDN of amines with the NH₂ group attached to a secondary and a tertiary carbon atom. This indicates that the HDN of alkylamines occurs on Brønsted acid sites.     

Hydrodenitrogenation and Hydrodesulphurization of Heavy Gas Oil Using NiMo/Al2O3 Catalyst Containing Phosphorus: Experimental and Kinetic Studies

In this work, a systematic study has been conducted to optimize the process conditions and to evaluate kinetic parameters for hydrodenitrogenation (HDN) and hydrodesulphurization (HDS) of heavy gas oil derived from Athabasca bitumen using NiMo/Al₂O₃ catalysts containing phosphorus (P). In the catalyst, the concentration of phosphorus was maintained at 2.7 wt%. Experiments were performed in a tickle‐bed reactor at the temperature, pressure and liquid hourly space velocity (LHSV) of 340‐420°C, 6.1‐10.2 MPa and 0.5‐2 h^?1, respectively. H₂ flow rate and catalyst weight were maintained constant at 50 mL/min and 4 g, respectively in all cases. Statistical analysis of all experimental data was carried out using ANOVA to optimize the process conditions for HDN and HDS reactions. Kinetic studies for HDN and HDS reactions were studied within the temperature range of 340‐400°C using the power law model as well as the Langmuir‐Hinshelhood model. The power law model showed that HDN and HDS of heavy gas oil follow first order kinetics. The activation energies for HDN and HDS reactions from the power law and Langmuir‐Hinshelwood models were 94 and 96 kJ/mol and 113 and 137 kJ/mol, respectively.     

Deep hydrodesulphurization and hydrogenation of diesel fuels on alumina-supported and bulk molybdenum carbide catalysts

Deep hydrodesulphurization (HDS) of diesel fuels has been carried out on P (Ni)-promoted or non-promoted Mo₂C-supported γ-Al₂O₃ and bulk Mo₂C under standard industrial conditions (613 K, 3 MPa). The effect of the promoter was investigated for different feedstocks on HDS and hydrogenation (HYD) with very low levels of sulfur. The temperature effect was also followed. The HDS conversion indicates that phosphorus promoted alumina supported carbide catalysts are as active as a commercial Co-Mo/Al₂O₃ catalyst for low levels of sulfur in the feed. Furthermore, the refractory compounds such as 4,6-dimethyldibenzothiophene are only transformed on molybdenum carbide catalyst in industrial conditions for hydrotreated gas oils. With gas oils with less than 50 wt ppm in sulfur, phosphorus promoted molybdenum carbide catalysts become more active than commercial catalysts for the HYD of the aromatic compounds and the HDS or the HDN of the feedstock.     

Zeolite beta synthesized with acid-treated metakaolin and its application in diesel hydrodesulfurization

A new type of zeolite beta (denoted as MB) with multi-pore system was synthesized by using in situ synthesized method from kaolin mineral in this study. NiW/Al₂O₃–MB and NiW/TiO₂–Al₂O₃–MB catalysts were prepared and the hydrodesulfurization (HDS) activities of these catalysts were evaluated with FCC diesel feed. The samples were characterized by N₂ physisorption, XRD, SEM, TPR, FT-IR spectroscopy of pyridine adsorption, HRTEM and XPS techniques. The HDS results showed that the MB-containing catalyst exhibited much higher HDS conversion (98.7%) than that of NiW/γ-Al₂O₃ (97.5%). The incorporation of TiO₂ into the composite supports further increased the HDS conversion (99.3%) of NiW/TiO₂–Al₂O₃–MB. The higher HDS activity was mainly associated with the appropriate ratio of B/L (Brönsted acid/Lewis acid) and the enhanced hydrogenation activity.     

Simulation of hydrodesulfurization using artificial neural network

Artificial neural network (ANN) is applied to investigate the hydrodesulfurization (HDS) process with light‐cycle oil as feed and NiMo/Al₂O₃ as catalyst. ANN models frequently work as a “black box” which makes the model invisible to users and always need significant data for training. In this work, a new ANN is proposed. The Langmuir–Hinshelwood kinetic mechanism is incorporated into the model so that the proposed ANN model is forced to follow the given reaction mechanisms. Both advantages of self‐learning ability of ANN and the existing knowledge of HDS were taken into account. Lengthy training process is minimised. Effects of operating temperature, pressure, and LHSV on the sulfur removal rate are studied. The inhibition of nitrogen compounds is also investigated. It is shown that the presence of nitrogen can significantly reduce the conversion rate of sulfur components, in particularly, hard sulfur such as 4,6‐DMDBT.     

Selectivity enhancement of Co-Mo/Al2O3 FCC gasoline hydrodesulfurization catalysts via incorporation of mesoporous Si-SBA-15

Mesoporous Si-SBA-15 was applied to enhance the FCC gasoline selective hydrodesulfurization (HDS) performance of conventional Co-Mo/Al₂O₃ catalysts and the physicochemical properties of the resulting catalyst were compared with those of Co-Mo/Al₂O₃ catalysts incorporated with macroporous kaolin, mesoporous Si-MCM-41 and microporous Si-ZSM-5. The selective HDS performances of all the catalysts were assessed with different FCC gasolines as feedstocks. The results showed that the HDS selectivity of the catalysts was closely related to the Mo sulfidation that depends on catalyst surface area and metal-support interaction. With the superior Mo sulfidation, the Co-Mo/Si-SBA-15-Al₂O₃ catalyst had the optimal HDS selectivity for not only the full-range FCC gasolines but also the heavy fractions thereof. The present article demonstrates the significance of enhancing Mo sulfidation in improving HDS selectivity and thus sheds a light on the development of highly selective HDS catalysts.     

Activity and thermal stability of sonochemically synthesized MoS2 and Ni-promoted MoS2 catalysts

Sonochemically synthesized MoS₂/Al₂O₃, which had a hydrodesulfurization (HDS) activity that was significantly greater than that of a catalyst prepared by impregnation, exhibited low thermal stability due to sintering of MoS₂ crystallites at high temperatures. The thermal stability was improved when the catalyst was promoted with Ni. In this study, we compared the activity and thermal stability of different Ni-promoted MoS₂ catalysts, which were prepared by addition of Ni to MoS₂ using either impregnation (IMP) or chemical vapor deposition (CVD). After use in the HDS of dibenzothiophene (DBT) at 673 K for 2 h, the initial activity of the un-promoted catalyst was partially lost, while that of the Ni-promoted catalysts was preserved. Ni added by CVD interacted more intimately with MoS₂ than Ni added by impregnation because CVD allowed selective deposition of Ni on the MoS₂ edge sites. Another advantage of the CVD method over the impregnation method is that Ni(CO)₄, which was used as the Ni precursor in the former method, could be decomposed at much lower temperatures than in the case of Ni(NO₃)₂, which was used in the impregnation method. As a result, Ni-promoted catalysts prepared using Ni-CVD showed superior HDS activity compared with those prepared using Ni-impregnation.     

Analysis and deep hydrodesulfurization reactivity of Saudi Arabian gas oils

Gas oils obtained from Arabian Light (AL-GO), Arabian Medium (AM-GO) and Arabian Heavy (AH-GO) crude oils were subjected to detailed analysis in terms of reactive and refractory sulfur, nitrogen, as well as aromatic species. Deep hydrodesulfurization (HDS) of these gas oils over SiO₂–Al₂O₃-supported CoMo and NiMo catalysts was studied using autoclave reactor either in one- or two-stage operations. AL-GO was easily and deeply desulfurized to 15 ppm over CoMo/Al₂O₃–SiO₂ (catalyst X) at 340 °C and 5 MPa (H₂) for 2 h. At the same conditions, AM-GO and AH-GO could be desulfurized to 70 and 78 ppm, respectively. Two-staged HDS, by combining CoMo and NiMo catalysts, in successive steps resulted in effective deep HDS. The replacement of hydrogen atmosphere after the first-stage (1 h) enhanced the AH-GO HDS during the second-stage (1 h) to 9 ppm. However, replacing the hydrogen in the second-stage with 5% H₂S in hydrogen inhibited the HDS, resulting in product sulfur content of 15 ppm. Analysis of sulfur species indicate that significant fraction of reactive and refractory sulfur species were removed during the first-stage whereas the remaining refractory sulfur species were removed during the second-stage. Kinetic analysis indicates overwhelming influence of refractive sulfur species on the overall HDS. The results from this study show that two-stage scheme with optimum catalysts in series can be applied to overcome the difficulty to achieve deep HDS of AH-GO.