Hydrodesulfurization of thiophene on carbon nanofiber supported Co/Ni/Mo catalysts

Co, Mo, NiMo and CoMo catalysts supported on alumina, fishbone and platelet carbon nanofibers (CNFs) have been prepared. The dispersion of the oxide phases was qualitatively studied and compared using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reducibility of the catalysts was studied by temperature programmed reduction (TPR). Hydrodesulfurization (HDS) of thiophene was used as a model reaction to compare the activity of different catalysts. The activity tests showed that the alumina supported catalysts exhibited higher activity compared to the corresponding CNF supported catalysts, and the NiMo catalysts were more active than the corresponding CoMo catalysts. The thiophene HDS activity was correlated with the dispersion of the molybdenum species and the reducibility of different catalysts. Interestingly, the CNF supported Co catalysts have higher thiophene HDS activity than the CNF supported Co(Ni)Mo catalysts.     

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.     

Comparative study of the activity of cobalt and nickel as promoters of HDS catalysts

A series of trimetallic (NiCoMo) hydrodesulphurisation supported catalysts were prepared using a successive impregnation method, varying the ratio of promoters Ni/(Ni + Co) and maintaining the ratio (Ni + Co)/Mo constant. Optima for higher thiophene hydrodesulphurisation activity were found for ratios Ni/(Ni + Co) of 0.7 and 0.8. It is suggested that the optima may be strongly dependent on method of catalyst preparation, and/or type of support employed. Presulphidation was found to increase the activity in NiMo more than in CoMo. Testing of commercial catalysts confirmed various differences between CoMo and NiMo catalysts.     

Supported (NiMo,CoMo)-carbide, -nitride phases: Effect of atomic ratios and phosphorus concentration on the HDS of thiophene and dibenzothiophene

A study on the catalytic properties of the transition metals (Ni,Co,Mo)-carbides, -nitrides for thiophene and dibenzothiophene hydrotreating was conducted. The (Ni,Co)-Mo carbides and the corresponding (Ni,Co)-Mo nitride phases showed a catalytic activity higher than conventional bimetallic (Ni,Co)-Mo sulfides. In addition, a study was done on the effect of the atomic ratios, i.e., 0.1 ≤ M⁺/(M⁺ + Mo) ≤ 0.9 where M⁺ stands for Ni or Co, and the concentration of promoters such as phosphorous, which was a structural stabilizing agent. The catalytic performance of the bimetallic NiMo and CoMo carbides and nitrides was studied using thiophene and dibenzothiophene hydrodesulfurization (HDS) as model reactions at 623 K and P = 1 atm. The catalytic activity of the dispersed carbide and nitride phases on the alumina carrier was more significant than that of the reference catalysts, alumina supported NiMo-S and CoMo-S. The metallic character of the NiMo and CoMo carbides was evidenced by their higher hydrogenation activity in thiophene HDS, while the nitrides favored both hydrogenation and hydrogenolysis type reactions.     

Magnesia-Supported Mo, CoMo and NiMo Sulfide Catalysts Prepared by Nonaqueous Impregnation: Parallel HDS/HDN of Thiophene and Pyridine and TEM Microstructure

MgO-supported Mo, CoMo and NiMo sulfide catalysts were prepared by impregnation using slurry MoO₃/methanol and solutions of Ni and Co nitrates in methanol. The catalysts exhibited very high hydrodesulfurization activity and low hydrodenitrogenation activity in competitive reactions of thiophene and pyridine. The promotion effect for HDS of Ni and Co was higher for our MgO-supported MoS₂ catalysts than for conventional Al₂O₃-supported catalysts. The specific features in the TEM images of MgO-supported catalysts as compared to conventional Al₂O₃-supported catalysts were fairly broad MoS₂ slab length distribution and the presence of unusually long MoS₂ slabs.     

Hydrodeoxygenation of stearic acid using Mo modified Ni and Co/alumina catalysts: Effect of calcination temperature

Abstract

The calcination temperature (Cal-Temp) plays a vital role in the performance of supported metal catalysts. In this work, the alumina supported Ni, NiMo, Co, and CoMo catalysts were prepared at different Cal-Temp. The catalysts were characterized by various techniques to identify the catalytically active different surface species to correlate their role in the hydrodeoxygenation of stearic acid. With increasing Cal-Temp, the metal dispersion was increased for Ni, NiMo, and CoMo catalyst (up to 973 K) and decreased for Co catalyst. With increasing Cal-Temp, the catalytic activity was thus increased for Ni and NiMo catalyst and decreased for Co catalyst. The activity of CoMo catalyst was, however, enhanced with rising Cal-Temp up to 973 K and declined slightly after that. The optimum Cal-Temp for Ni, NiMo, Co, and CoMo catalyst was found to be 1023 K, 973 K, 773 K, and 973 K. The reaction followed the decarbonylation route over active metallic centers (Ni and Co) and the HDO route over oxophilic M²⁺?MoO₂ (M = Ni/Co) and reducible cobalt oxide species. The C₁₇ alkane was thus the principal product over Ni catalyst, whereas C₁₈ alkane was the primary product over CoMo and NiMo catalyst. In contrast, both C₁₇ and C₁₈ alkanes were significant over Co catalyst.     

Hydrotreating of gas oil on SBA-15 supported NiMo catalysts

The siliceous and the metal substituted (B or Al)-SBA-15 molecular sieves were used as a support for NiMo hydrotreating catalysts (12 wt.% Mo and 2.4 wt.% Ni). The supports were characterized by X-ray diffraction (XRD), scanning electron microscopy and N₂ adsorption–desorption isotherms. The SBA-15 supported NiMo catalysts in oxide state were characterized by BET surface area analysis and XRD. The sulfided NiMo/SBA-15 catalysts were examined by DRIFT of CO adsorption and TPD of NH₃. The HDN and HDS activities with bitumen derived light gas oil at industrial conditions showed that Al substituted SBA-15 (Al-SBA-15) is the best among the supports studied for NiMo catalyst. A series of NiMo catalysts containing 7–22 wt.% Mo with Ni/Mo weight ratio of 0.2 was prepared using Al-SBA-15 support and characterized by BET surface area analysis, XRD and temperature programmed reduction and DRIFT spectroscopy of adsorbed CO. The DRIFT spectra of adsorbed CO showed the presence of both unpromoted and Ni promoted MoS₂ sites in all the catalysts, and maximum “NiMoS” sites concentration with 17 wt.% of Mo loading. The HDN and HDS activities of NiMo/Al-SBA-15 catalysts were studied using light gas oil at temperature, pressure and WHSV of 370 °C, 1300 psig and 4.5 h⁻¹, respectively. The NiMo/Al-SBA-15 catalyst with 17 wt.% Mo and 3.4 wt.% of Ni is found to be the best catalyst. The HDN and HDS activities of this catalyst are comparable with the conventional Al₂O₃ supported NiMo catalyst in real feed at industrial conditions.     

Effect of EDTA on hydrotreating activity of CoMo/γ-Al2O3 catalyst

γ-Al₂O₃ supported Co (0–4.5 wt%) Mo (9.0 wt%) sulfide catalysts were prepared in the presence and the absence of ethylenediaminetetraacetic acid (EDTA). The hydrodenitrogenation (HDN) activity of these catalysts was studied in the model reaction of 2,6-dimethylaniline (DMA) at 300 °C under 4 MPa. The CoMo/Al₂O₃ catalysts prepared with the EDTA showed higher HDN of DMA than those prepared without EDTA. The maximum of 36% increase in rate constant of HDN of DMA was observed over the catalyst with 3% Co prepared using EDTA. The FT-IR spectroscopy of adsorbed CO on CoMo catalysts showed that EDTA addition promoted the formation of catalytically active “CoMoS” phase as evidenced from increases in intensity of band at 2070 cm⁻¹, which is maximum for 3% Co loaded catalysts. The HDN and hydrodesulfurization (HDS) activity of 3% Co loaded catalyst prepared using EDTA was tested and compared with those catalyst prepared without EDTA in a trickle bed reactor using heavy gas oil derived from Athabasca bitumen in the temperature range 370–400 °C and 8.8 MPa. Improved HDN and HDS conversion of heavy gas oil was obtained for the catalyst prepared with EDTA.     

Effect of Zr-SBA-15 support on catalytic functionalities of Mo, CoMo, NiMo hydrotreating catalysts

SBA-15 and ZrO₂ (10–50 wt.%) containing SBA-15 mesoporous materials were prepared by direct and post-synthesis methods. Characterization using low angle XRD, pore size distribution, CO₂ chemisorption indicate that hexagonal mesoporous structure is retained even after ZrO₂ addition (25 wt.%). Mo, CoMo and NiMo catalysts prepared using these supports were examined by XRD, oxygen chemisorption, temperature programmed reduction (TPR). The catalysts were tested for hydrodesulfurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene. HDS of thiophene for 8%Mo, 3%Co8%Mo, and 3%Ni8%Mo increases with increasing ZrO₂ loading in SBA-15 up to 25 wt.%. Oxygen chemisorption and TPR hydrogen consumption indicated that the molybdenum dispersion and anion vacancies, and catalytic activities are significantly influenced by ZrO₂ content in Zr-SBA-15. A comparison indicated that TiO₂-SBA-15, ZrO₂-SBA-15 supported CoMo catalysts show higher activities for hydrodesulfurization.     

On the formation of cobalt–molybdenum sulfides in silica‐supported hydrotreating model catalysts

Model catalysts, consisting of a conducting substrate with a thin SiO₂ layer on top of which the active catalytic phase is deposited by spincoating impregnation, were applied to study the formation of the active CoMoS phase in HDS catalysts. The catalysts thus prepared showed representative activity in the hydrodesulfurization of thiophene, confirming that these models of HDS catalysts are realistic. Combination of the sulfidation behaviour of Co and Mo studied by XPS and activity measurements shows that the key in the formation of the CoMoS phase is the retardation of the sulfidation of Co. Complexing Co to nitrilotriacetic acid complexes retarded the Co sulfidation, resulting in the most active catalyst. Due to the retardation of Co in these catalysts, the sulfidation of Mo precedes that of Co, thereby creating the ideal conditions for CoMoS formation. In the CoMo catalyst without NTA the sulfidation of Co is also retarded due to a Co–Mo interaction. However, the sulfidation of Mo still lags behind that of Co, resulting in less active phase and a lower activity in thiophene HDS. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Review of Deep Hydrodesulfurization Catalysis

The increasing importance of hydrodesulfurization (HDS) in petroleum processing in order to produce clean-burning fuels has led to a surge of research on the chemistry and engineering of HDS. Most of the earlier works are focused on catalyst characterization by physical methods; on low-pressure reaction studies of compounds like thiophene having relatively high reactivities; on process development; or on CoMo, NiMo, or NiW catalysts supported on alumina, often doped by fluorine or phosphorus. Almost all the reviews have concentrated on alumina-supported CoMo, NiMo, and NiW sulfide catalysts for hydrotreating. Even reviews that are not limited to the above catalytic systems essentially deal with studies of simple compounds like thiophene.     

TiO2-Supported Mo Model Catalysts: Ti as Promoter for Thiophene HDS?

The combination of thiophene hydrodesulfurization (HDS) activity measurements and X-ray photoelectron spectroscopy on flat model systems of sulfided HDS Mo catalysts showed that sulfided Ti-species can act as a promoter in the same way as Co and Ni, although less effectively. This explains the higher thiophene HDS activity and hydrogenation selectivity of Mo/TiO₂ compared with Mo/Al₂O₃, while for Ni-promoted Mo catalysts the difference between the two supports is negligible.     

磷添加方式对NiMo/Al2O3催化剂加氢脱硫性能的影响

采用分步浸渍法制备了不同磷添加方式改性的NiMo/Al₂O₃催化剂,在固定床微反装置上考察了该系列催化剂对焦炉煤气中噻吩加氢脱硫（HDS）性能的影响,采用BET、X射线衍射（XRD）、H₂程序升温还原（H₂-TPR）、NH₃程序升温脱附（NH₃-TPD）、C₄H₄S(H₂)程序升温脱附[C₄H₄S(H₂)-TPD]、X射线光电子能谱（XPS）、高清透射电镜（HRTEM）和拉曼（Raman）等分析手段对催化剂进行表征。结果表明,不同磷添加方式制备NiMo/Al₂O₃催化剂的HDS性能存在较大差异。其中,催化剂PNi-Mo/Al和PMo-Ni/Al表面弱吸附解离活性位增强,对焦炉煤气中噻吩有较好的低温加氢脱硫活性,以含292.5mg/m³噻吩的模拟焦炉煤气为原料时,PNi-Mo/Al在250℃下对噻吩的脱硫率达61%。对于PNi-Mo/Al和PMo-Ni/Al催化剂,先浸渍P、Ni或者P、Mo时,P优先和载体Al₂O₃作用,减弱了活性金属组分Ni、Mo与载体间的相互作用,而又防止Ni或者Mo与载体间相互作用过低而聚集,提高了Ni、Mo在载体表面的均匀分散,生成能够促进硫化形成Ⅱ型活性相Ni-Mo-S的NiMoO₄物种。NiMoO₄和MoO₃之间的协同作用提高了催化剂的硫化度,使HDS活性得以提高。     

Effect of supercritical deposition synthesis on dibenzothiophene hydrodesulfurization over NiMo/Al2O3 nanocatalyst

The synthesis of two NiMo/Al₂O₃ catalysts by the supercritical carbon dioxide/methanol deposition (NiMo‐SCF) and the conventional method of wet coimpregnation (NiMo‐IMP) were conducted. The results of the physical and chemical characterization techniques (adsorption–desorption of nitrogen, oxygen chemisorption, XRD, TPR, TEM, and EDAX) for the NiMo‐SCF and NiMo‐IMP demonstrated high and uniform dispersed deposition of Ni and Mo on the Al₂O₃ support for the newly developed catalyst. The hydrodesulfurization (HDS) of fuel model compound, dibenzothiophene, was used in the evaluation of the NiMo‐SCF catalyst vs. the commercial catalyst (NiMo‐COM). Higher conversion for the NiMo‐SCF catalyst was obtained. The kinetic analysis of the reaction data was carried out to calculate the reaction rate constant of the synthesized and commercial catalysts in the temperature rang of 543–603 K. Analysis of the experimental data using Arrhenius' law resulted in the calculation of frequency factor and activation energy of the HDS for the two catalysts. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Bio gas oils with improved low temperature properties

During hydrodeoxygenation of triglycerides to motor fuel the isomerization reactions have an important role, since the cold flow properties of the product are improved significantly by increase of isoparaffin content of the product in gas oil boiling range. Accordingly, the aim of our research program was to select and investigate suitable catalyst(s) for producing relatively high isoparaffin containing product for a long time of preserved activity. Both not-presulphided CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts have isomerization activity, however, in the case of CoMo/Al₂O₃ catalyst triglyceride conversion is higher by 25.1-30.5 abs%, as well as yields by 24.2-24.6 abs% corresponding by 0.18-0.33 higher i-/n-paraffin ratio than for NiMo/Al₂O₃ under favorable conditions. Thereby products with more advantageous cold flow properties can be produced on CoMo/Al₂O₃ catalyst.     

Catalytic activity of Co,Mo and CoMo supported on NaY zeolite: hydrodesulfurization of gas oil at high pressure

Three series of Co/NaY, Mo/NaY and CoMo/NaY zeolite catalysts with variable metal content, prepared by a conventional impregnation method, were characterized by XRD, IR spectroscopy (oxide state) and acidity measurements (sulfide state), and tested in hydrodesulfurization (HDS) of gas oil at high pressure in the temperature range 275–350°C. The combined results of surface area, XRD and IR showed that in the catalysts with high metal loading a small loss in crystallinity and a partial blockage of the zeolite supercages were produced by Mo oxide species. The number of acid sites, which was lower for the Co/NaY than for the Mo/NaY catalysts, increased with increasing Co or Mo loading, but the strength of the acid sites was stronger for the Co/NaY series. HDS specific activities of the Co/NaY and Mo/NaY monometallic catalysts reached a maximum at very low loadings of Co ( 0.10 at. nm^–2) or Mo ( 0.16 at. nm^–2) by the double action of the metal sulfide species and the strong acid sites generated on the zeolite by the Co or Mo incorporation. In the binary CoMo/NaY catalysts, the synergy between Co and Mo species was significant for high Mo contents only.     

Rationalizing the catalytic performance of γ-alumina-supported Co(Ni)–Mo(W) HDS catalysts prepared by urea-matrix combustion synthesis

A comparative study of the influence of Co (or Ni) promoter loadings and the effect of different sulfurizing agents and sulfurizing temperatures on the structure, morphology and catalytic performance of Mo- or W-based hydrodesulfurization (HDS) catalysts was carried out. Catalyst performance using a tubular fixed-bed reactor and the HDS of thiophene as a model reaction was evaluated. The oxidic and sulfurized states of the HDS catalysts were characterized by laser Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high resolution transmission electron microscopy (HRTEM). It has been found that the urea-matrix combustion (UMxC) synthesis is a simple tool for preparing supported catalysts in a short period of thermal treatment. Several consecutive stages such as urea melting, metal precursor dissolution and chemical reactions take place before and upon combustion process. The C₄H₄S/H₂-activated Co- (or Ni-) promoted MoS₂ (or WS₂) catalysts present a strong synergistic effect (SE) when the Co (or Ni)/Mo (or W) molar ratio is near to 0.5, whereas the C₄/C ₄ ⁼ molar ratios display a weak antagonistic effect. Alumina-supported Ni–W catalyst showed an optimal SE 2.5 times higher than those for Co (or Ni)-promoted Mo HDS catalysts. The kinetic parameters for thiophene-HDS reaction were also determined, suggesting that the C–S bond cleavage reaction for alumina-supported Co(Ni)–Mo HDS catalysts and H₂ activation reaction for Ni-promoted WS₂catalysts play an important role in the rate-limiting step.     

Preparation of Co–Mo/B2O3/Al2O3 catalysts for hydrodesulfurization: Effect of citric acid addition

The effect of citric acid (CA) addition was studied on the HDS of thiophene over Co–Mo/(B)/Al₂O₃ catalysts. The catalysts were characterized by means of LRS, Mo K-edge EXAFS, NO adsorption capacity measurements, and UV–vis spectra. The catalysts were subjected to a chemical vapor deposition (CVD) technique using Co(CO)₃NO as a precursor of Co in order to get deeper insights into the effect of citric acid addition. It was shown that the HDS activity was enhanced by the citric acid addition up to the CA/Mo mole ratio of around 1 and leveled off with further addition. The amount of Co anchored by the CVD was increased by the addition of citric acid, suggesting an increase in the dispersion of MoS₂ particles on the catalyst by the simultaneous presence of Co, Mo and citric acid, in conformity with the increase in the NO adsorption capacity. In contrast to Co–Mo catalysts, the edge dispersion of MoS₂ particles in Mo/B/Al₂O₃ was not affected by the addition of citric acid. The LRS, UV–vis spectra and Mo K-edge EXAFS showed that Co–CA and Mo–CA surface complexes are formed by the addition of citric acid. The Co–CA surface complex is more preferentially formed on CoMo/Al than on CoMo/B/Al, in agreement with a greater promoting effect of citric acid at a lower CA/Mo mole ratio for CoMo/Al than for CoMo/B/Al.     

Hydrotreating of heavy gas oil using CoMo/γ-Al2O3 catalyst prepared by equilibrium deposition filtration

CoMo/γ-Al₂O₃ catalyst containing 16.0 wt% MoO₃ and 3.2 wt% CoO was prepared by equilibrium deposition filtration method (EDF). The CoMo oxidic catalyst was characterized by elemental analysis, N₂ adsorption, XRD, and TPR. The sulfided catalyst was characterized by FTIR of adsorbed CO at 30 °C. Hydrodesulfurization (HDS) and hydrodearomatization activities were evaluated for heavy gas oil (HGO) in a trickle bed reaction system using the following conditions: reaction temperatures of 340, 360, 380 and 400 °C, a reaction pressure of 20, 35, 50 and 65 bar, a liquid hourly space velocity (LHSV) of 1.0, 1.5, 2.0, 2.5 and 3 h⁻¹ and a H₂/feed ratio of 400 L L⁻¹. The experimental results were used to determine apparent reaction orders and activation energies. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared with the conventionally prepared CoMo/γ-Al₂O₃ catalyst containing similar wt% of MoO₃ and CoO. The CoMo catalyst prepared by equilibrium deposition filtration method has higher HDS and HDA rate constants than the conventional catalyst due to an improved dispersion of MoS₂.     

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.