Catalysts For Hydrodesulfurization Of Thiophene Research Articles

Kinetics of thiophene hydrodesulfurization over a supported Mo–Co–Ni catalyst

In this study, the kinetics of thiophene (TH) hydrodesulfurization (HDS) over the Mo–Co–Ni-supported catalyst was investigated. Trimetallic catalyst was synthesized by pore volume impregnation and the metal loadings were 11.5 wt % Mo, 2 wt % Co, and 2 wt % Ni. A large surface area of 243 m 2 /g and a relatively large pore volume of 0.34 cm 3 /g for the fresh Mo–Co–Ni-supported catalyst indicate a good accessibility to the catalytic centers for the HDS reaction. The acid strength distribution of the fresh and spent catalysts, as well as for the support, was determined by thermal desorption of diethylamine (DEA) with increase in temperature from 20 to 600 °C. The weak acid centers are obtained within a temperature range between 160 and 300 °C, followed by medium acid sites up to 440 °C. The strong acid centers are revealed above 440 °C. We found a higher content of weak acid centers for fresh and spent catalysts as well as alumina as compared to medium and strong acid sites. The catalyst stability in terms of conversion as a function of time on stream in a fixed bed flow reactor was examined and almost no loss in the catalyst activity was observed. Consequently, this fact demonstrated superior activity of the Mo–Co–Ni-based catalyst for TH HDS. The activity tests by varying the temperature from 200 to 275 °C and pressure from 30 to 60 bar with various space velocities of 1–4 h −1 were investigated. A Langmuir–Hinshelwood model was used to analyze the kinetic data and to derive activation energy and adsorption parameters for TH HDS. The effect of temperature, pressure, and liquid hourly space velocity on the TH HDS activity was studied.

Temperature sensitive synthesis of γ-Al2O3support with different morphologies for CoMo/γ-Al2O3catalysts for hydrodesulfurization of thiophene and 4,6-dimethyldibenzothiophene

Two different kinds of γ-Al2O3precursors: stick-like ammonium aluminum carbonate hydroxide and willow leaf-like boehmite could be selectively synthesizedviaa facile hydrothermal method by just adjusting reaction temperature.

A controllable synthesis of nitrogen-doped mesoporous carbon supported MoS2catalysts for hydrodesulfurization of thiophene

A highly active and stable catalyst for hydrodesulfurization (HDS) was developed based on thein situformation of MoS2on nitrogen-doped mesoporous carbon (MoS2/NMC).

Modeling the kinetics of sulfidation over NiMo/Al2O3 catalyst for thiophene hydrodesulfurization

A kinetic model has been developed for the sulfidation of NiMo/Al2O3 hydrodesulfurization (HDS) catalyst, which quantitatively establishes a relationship between the HDS activity and sulfidation conditions. The model parameters were estimated by fitting a series of experimental thiophene HDS conversion data over the catalysts sulfurized under different operations. The results show that the developed model satisfactorily predicts the HDS conversion with a total average relative deviation of less than 4 %. Moreover, parametric studies were made to validate the accuracy of the model. The comparison results show that the proposed model is fairly effective in simulating the sulfidation process. It is expected that the model will be used to guide the sulfidation research of supported Mo-based catalysts and to optimize laboratory/pilot-plant sulfiding procedures.

The Support Effect on Hydrogenolysis of Thiophene and Gas–Oil

Results are reported on the support effect on the catalytic activity in thiophene hydrodesulfurization (HDS) of sulfided Ni-Mo catalysts supported on pure niobia, mixed oxides of Nb2O5-TiO2 prepared by sol-gel method, and Nb2O5/TiO2 and Nb2O5/Al2O3 prepared by surface deposition. The prepared samples were characterized using N2 adsorption at −196°C, X-ray diffraction (XRD), and temperature-programmed reduction (TPR) techniques. This study showed activity variation as a function of support composition. The activity of niobia-rich catalysts was no longer promoted by the synergy between Ni and Mo. The absence of synergy between molybdenum and nickel on niobia can be explained by the strong interaction of each metal with niobia at the expense of interaction with each other. It was found that 5 wt% Nb2O5/TiO2-supported catalyst was the better catalyst for thiophene HDS. It was shown that by means of an adequate support design it is possible to significantly increase the functionalities of HDS catalysts. Semiconducting supports like TiO2 can improve the HDS activity by exerting electronic effects on the active phase, helping in this way the formation of sulfur vacancies. The 5 wt% Nb2O5/TiO2 was also tested at high pressure with gas oil feedstock. It is observed with the hydrogeolysis of sulfur compounds against time-on-stream that the activity of this catalyst decreases fast with time.

The effect of Co-promotion on MoS 2 catalysts for hydrodesulfurization of thiophene: A density functional study

We present density functional theory (DFT) calculations of the hydrogenation (HYD) and direct desulfurization (DDS) pathways of thiophene hydrodesulfurization (HDS) over cobalt-promoted MoS 2. We find that the Co–Mo–S edge in its equilibrium state under HDS conditions is reactive toward both hydrogenation and C–S bond scission without the initial creation of vacancies. This can be accomplished such that additional S is bound to the Co–Mo–S subsequent to C–S bond scission and then removed in the final reaction step. We find thus that coordinatively unsaturated sites (CUS) are present in the equilibrium structure, and at these sites HDS can take place without sulfur removal in the first step. No traditional vacancies are formed and the present mechanism is therefore very different from the previously proposed vacancy mechanisms requiring the initial creation of a sulfur vacancy for the reaction to proceed. We find that Co-promotion decreases the barrier of hydrogenation reactions and active site regeneration but increases the barrier of C–S-scission reactions. The net result of Co promotion is found to be an increase in the hydrogenation activity and also of the relative importance of the DDS pathway. We compare our results to available experimental information and find a number of consistencies and parallels. Therefore, we can rationalize the promoting effect of Co such that at the Co–Mo–S edge, good hydrogenation properties are combined with the ability to bind additional sulfur upon C–S-scission. Finally, we propose that the interactions between the Co-promoted S-edge and the non-promoted Mo-edge may play a role in the hydrogenation pathway.

Study of the Role of Lanthanum Containing Titania in Hydrogenolysis of Thiophene and Gas Oil

Pure La2O3 and La2O3-TiO2 mixed oxides are prepared by sol-gel method. Hydrodesulfurization catalysts containing 8 wt% MoO3 and 3 wt% NiO are prepared using these oxides and characterized by Brunauer, Emmett, and Teller (BET) surface area, pore volume, X-ray diffraction, differential thermal analysis, Fourier transform infrared and scanning electron microscopy. The effects of support composition have been investigated in order to determine their influence on hydrodesulfurization catalytic process. Hydrodesulfurization of thiophene model molecule reaction was carried out in a micro-catalytic reactor at 250°C–425°C and atmospheric pressure. Sulfided catalysts showed a wide range of activity variation as a function of support composition, which established that NiMo sulfided active phases strongly depend on the nature and composition of support. It is found that 10% La/Ti supported catalyst was the better catalyst for thiophene hydrodesulfurization. It was also tested at high pressure with a real feed Gas oil.

MoS2–Ni Nanocomposites as Catalysts for Hydrodesulfurization of Thiophene and Thiophene Derivatives

Nanocomposites for the petroleum industry are presented. MoS2 nanotubes with Ni nanoparticles deposited on their surface (see figure) are shown to be very effective for hydrodesulfurization of thiophene and thiophene derivatives at relatively low temperatures, providing a new way of eliminating sulfur pollution and thus enabling the highly efficient and clean utilization of organosulfur compounds.

Cobalt-containing smectite-like mesoporous material as a new type of catalyst for hydrodesulfurization of thiophene

Cobalt‐containing mesoporous smectite‐like material (SM(Co)) was prepared by a hydrothermal method and used as a catalyst for hydrodesulfurization (HDS) of thiophene. It is active by itself and produces mainly butenes and a small amount of n-butane. When platinum is added to this material, the HDS activity is enhanced by 50%, while the product distribution does not change so much. The platinum‐loaded sample should have two types of active sites, one originally present in the smectite‐like material and the other with platinum, the latter being different in nature from a sample of platinum supported on silica gel. Thus, the SM(Co) and Pt/SM(Co) samples are new types of HDS catalysts.

Surface Properties and Activities of Ru/Al2O3 Catalysts for Hydrodesulfurization of Thiophene.

The activities of Ru/Al2O3 catalysts for hydrodesulfurization (HDS) of thiophene were studied, using a differential microreactor at atmospheric pressure. The surface properties of the catalysts were determined by NH3-TPD, XPS analysis, and IR spectroscopy. The Ru/Al2O3 catalysts were pretreated by three different methods: oxidized in air and subsequently reduced in H2 (Ru-OR catalyst), directly reduced in H2 (Ru-R catalyst), and sulfided in 10% H2S/H2 (Ru-S catalyst). All of the catalysts, pretreated at a temperature of 300°C, were among the most active, while the activity of Ru-S at 400°C was the least. Mild sulfidation at 300°C in flowing 10% H2S/H2 promoted the activity of the Ru/Al2O3 catalysts for the HDS of thiophene, while severe sulfidation at 400°C decreased the activity. Two NH3 peaks at low and middle temperatures and one peak of N2 and H2 at high temperature were observed for the three kinds of the catalysts in the NH3-TPD study. The XPS analysis showed that the low-, middle-, and high-temperature peaks in NH3-TPD were assigned to RuO2, acid sites on alumina, and Ru0 metal, respectively. The mass spectrometry indicated that the high-temperature peak of NH3-TPD consisted of N2, formed from the decomposition of NH3 on the ruthenium sites of the catalysts. The FTIR study indicated that the low-temperature peak of NH3-TPD was related to Lewis acid sites of the Ru catalysts. The HDS activity of the Ru/Al2O3 catalysts, for the HDS of thiophene, depended on the metallic ruthenium on the surface of the catalysts, rather than surface acidity measured in NH3-TPD.

Effect of fluoride on the structure and activity of NiW/Al 2O 3 catalysts for HDS of thiophene and HDN of pyridine

The effect of adding different amounts of fluoride to a γ-alumina used as support of NiW/Al 2O 3 catalysts was investigated using X-ray diffraction, diffuse reflectance spectroscopy (DRS), infrared spectroscopy of adsorbed NO (IR-NO), X-ray photoelectron spectroscopy (XPS), surface acidity, specific surface area and catalytic activity measurements. The catalytic activity was evaluated by two model reactions, namely thiophene hydrodesulfurization (HDS) and pyridine hydrogenation (HDN), in the temperature range 573–623 K using a flow system operated at 2 MPa (HDS) or 3 MPa (HDN) total pressure. DRS results of the oxidic precursors suggested that the effect of fluoride incorporation to the alumina support is that it increases slightly the octahedrally coordinated fractions of Ni and W. The XPS results of the sulfided catalysts showed that the dispersion of the Ni and W phases decreased progressively with increasing fluoride content. This technique also showed that these phases were only partially sulfided under the present experimental sulfiding conditions, and that the extent of sulfidation of such phases apparently tends to decrease slightly with increasing fluoride content, in contrast with the results suggested by the IR-NO spectra. The sulfur content of sulfided samples, as measured by chemical analysis, revelated that the sulfidation degree increased only slightly with increasing fluoride content. The activity for thiophene HDS was almost invariant with fluoride addition, but the subsequent hydrogenation of the intermediate products (butenes) was found to decrease linearly with the fluoride content. Possible interpretations for these changes in activity and selectivity, which reflect changes in the relative distribution of the different active sites for the two reactions, are discussed in relation with the structural variations of the active phases described above. In contrast, the activity for pyridine HDN increased considerably with the incorporation of small amounts of fluoride; this increase is mainly attributed to the increase in surface acidity which was observed with fluoride addition.

Structure and catalytic activity of regenerated spent hydrotreating catalysts

Two spent catalysts, obtained from different hydrodemetallation operations, were regenerated by two different treatments, viz. 2% (V/V) O 2/N 2 and air. One spent catalyst (B), contained 3 wt% V and 15 wt% C, while the other (H) contained 10 wt% V, 14 wt% C and 8 wt% Fe. After regeneration in the O 2/N 2 stream, catalyst B showed essentially complete recovery of its original surface area, whereas catalyst H showed only 70% recovery. Both catalysts showed substantial losses in surface area by the air treatment. Catalytic activity tests on the regenerated catalysts for hydrodesulfurization of thiophene and for hydrogenation of 1-hexene showed low recovery of activities, even for the regenerated catalyst in which the surface area had been completely recovered. X-ray diffraction analyses of the spent-regenerated catalysts revealed substantial changes in catalyst structure. Surface area and catalytic activity results were qualitatively explained by these catalyst structural changes.

Catalytic desulfurization (Part 14). Hydrodesulfurization of thiophene over metal-Y zeolite catalysts.

The reduced metal Y zeolites (Me°Y), such as Ni°Y, Co°Y, Cu°Y and Ag°Y, manifested higher catalytic activity than commercial CoMoAl hydrodesulfurization catalyst for hydrodesulfurization of thiophene. The order of the activity of Me°Y was Ni°Y>Co°Y>Cu°Y> Ag°Y>Fe°Y, Cr°Y≈0. The catalytic activity of Me°Y decrcased with increase in the pulse number, but catalytic deactivation against the pulse number improved significantly with increase in the calcination temperature of MeY. The effect of addition of NiO or MoO3 (5wt%) by impregnation on the catalytic activity of Me°Y for hydrodesulfurization of thiophene was examined, but no remarkable promoting effect of NiO or MoO3 was observed.