Higher HDS Activity Research Articles

Effects of lanthanum and ethylenediamine tetraacetic a cid

Using nickel-tungsten as active metals and TiO₂-Al₂O₃ as the support, Ni-W/TiO₂-Al₂O₃ catalysts for the hydrodesulfurization of heavy oil were prepared by wetness impregnation. The effects of the modification of lanthanum, ethylenediamine tetraacetic acid (EDTA)and La in cooperation with EDTA on the structure and hydrodesulfurization performance of the catalysts were investigated. The catalysts were characterized by XRD, BET, H₂-TPR and SEM. The results indicated that La and EDTA could weaken the interaction between support and active component, facilitate the reduction of active component, and benefit the formation of Ni-W-S phase. Addition of La or EDTA could increase the surface area and suppress the agglomeration of active metals on surface, forming smaller and highly dispersed active phase particles. The La, EDTA and combined La and EDTA modified catalysts possessed higher HDS activity than Ni-W sample, Ni-W-La-E catalyst had the highest HDS activity, and its thiophene conversion reached 99.7%.

On the electronic properties and catalytic activity of MoS2–C3N4 materials prepared by one-pot reaction

MoS2–C3N4 composite materials with Mo content from 0.3 to 9 wt% have been prepared by means of one-pot synthesis from ammonium thiomolybdate (NH4)2MoS4 and urea-thiourea mixture. The solids were characterized by several physical techniques and tested in the thiophene hydrodesulfurization model reaction (HDS) and in photocatalytic hydrogen evolution reaction (PHER). Transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) show that even at the smallest Mo contents the solids contain individual MoS2 and C3N4 phases. As attested by powder X-ray diffraction (XRD), addition of (NH4)2MoS4 impacts the properties of obtained C3N4, probably at the growth stage, leading to more disordered carbon nitride phase. However, the materials demonstrate electronic properties close to a superposition of two separate MoS2 and C3N4 phases, as follows from the results of UV–visible diffuse reflectance spectroscopy (UV–vis DRS) combined with Ultraviolet and X-ray photoelectron spectroscopies (UPS, XPS). The band alignment diagram constructed from the UV–vis DRS, XPS and UPS data is of staggered type, the valence band edge of MoS2 being located above that of C3N4. Composite materials have high thiophene HDS activity, increasing in step with the Mo content, which proves fine dispersion of MoS2 phase and good availability of MoS2 edges to the reactants. By contrast, PHER activity first increases and then decreases with the Mo loading, reflecting on the competition between the ability of MoS2 to promote associative desorption of hydrogen and its role as a charge carriers recombination sink.

Dispersed Ni-Mo sulfide catalysts from water-soluble precursors for HDS of BT and DBT via in situ produced H2 under Water gas shift conditions

The Ni-Mo catalysts formed in invert sulfur-containing emulsions through the high-temperature decomposition of water-soluble metal precursors were tested in HDS of benzo- and dibenzothiophenes via in situ hydrogen under WGSR conditions. The formation of highly dispersed sulfide species, fully covered by Ni atoms, as well as separate Ni and Mo sulfides was proved by FT-IR, XRD, TEM, EDX mapping, and XPS techniques. The catalytic evaluation revealed the high HDS activity at 380−420 °C, p(CO) = 5 MPa, the water content of 20 wt.%, and CO:H2O molar ratio of 1.8. The catalytic behavior was estimated depending on the reaction conditions, structural features, and active phase composition. As revealed from products distribution, the lower temperature and reaction time favor the HYD reaction pathway, while the surfactant leads to the dibenzothiophene transformation through the DDS reaction route at higher temperatures. The catalysts were found to be reused at least 6 cycles in the sulfur-assisted HDS of dibenzothiophene.

Influence of alumina precursor on silicon capacity of NiMo/γ-Al2O3 guard bed catalysts for gas oil hydrotreating

Abstract The influence of alumina precursors on NiMo/γ-Al2O3 catalysts for silicon removal from gas oil have been studied. Alumina precursors were prepared by hydrothermal treatment of gibbsite, precipitation of aluminum nitrate by ammonia and precipitation of aluminum nitrate in autoclave. Alumina precursors, supports and catalysts were studied by XRD, nitrogen adsorption-desorption, IR spectroscopy, UV–vis, XPS, SEM, HRTEM. Series of NiMo/γ-Al2O3 catalysts differed in preparation method of alumina precursors was tested in hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane as a model silicon compound. It was shown that prepared alumina precursors were boehmites and dawsonite, which had different particle size. The supports prepared from these alumina precursors were γ-Al2O3 with different particles size. It was shown that there was a dependence of the surface area of the support on the size of primary particles measured by XRD. The higher surface area results in the higher content of OH groups and silicon sorption capacity. Morphology of the sulfide active component also depends on the size of primary particles. The higher length of the particles, the higher slab length of NiMoS phase. The catalyst with the lowest particle size of alumina and highest length of active component had the highest HDS activity.

Application of Uniform Design Method in the Optimization of Hydrothermal Synthesis for Nano MoS2 Catalyst with High HDS Activity

The optimization of catalyst synthesis conditions using traditional single factor method involves extensive experimental time and costs. To overcome the drawbacks, a uniform design method was applied in the hydrothermal synthesis of nano MoS2 catalyst. An optimal synthesis condition is reached with only a few trials. Catalyst synthesis temperature is reduced to 200 °C. The catalyst synthesized at the screened condition shows high hydrotreating activities. The results conclude that the catalyst has thread-like slabs with a lattice structure that is less mature than fully developed MoS2. The characterization results indicate that the appearance of such structure may be due to the weak links of successive MoS2 nuclei. The high catalytic activity is a result of the layered structure and a significantly large number of defects on the slabs.

Synthesis of Porous NiMo Sulphide Act as HDS Catalyst by Alcohol Supercritical Drying Technique

Porous NiMo sulphide was successfully synthesized from ethanol supercritical fluid drying technique using (NH4)2MoS4and Ni(NO3)2as the precursors. It was shown that the NiMo sulphide had extremely high porosity and the specific surface area was 322 m2•g-1. The results of DBT hydrodesulfurization experimental showed that the porous NiMo sulfide prepared had high HDS activity, which was 2.78 times higher than that of a commercialized supported catalyst.

HDS of 4,6-DMDBT over NiMoP/(x)Ti-SBA-15 catalysts prepared with H3PMo12O40

HDS of 4,6-DMDBT over NiMoP/SBA-15 and NiMoP/(x)TiSBA-15 catalysts prepared using an heteropolyacid (H3PMo12O40) and nickel citrate (C12H10Ni3O14) as Mo and Ni precursors was studied. To analyze the effect of calcination temperature on HDS activity, catalysts noncalcined and calcined at 773 K were prepared. The performance of the different catalysts during the hydrodesulfurization of 4,6-dimethyldibenzothiophene was compared with that of a reference catalyst prepared by impregnation with a solution containing ammonium heptamolybdate and nickel nitrate. Kinetic parameters for the HDS of 4,6-DMDBT were estimated using a simplified kinetic model. The catalysts were characterized by N2 physisorption, X-ray diffraction, Raman, and IR of adsorbed CO at ∼100 K. The results show that for catalysts supported on pure SBA-15 the noncalcined catalyst prepared with H3PMo12O40 (NiMoP(H-nc)/SBA-15) presents the highest number of active sites, the higher apparent reaction rate constant for the hydrogenation route, and therefore the best 4,6-DMDBT HDS activity. In contrast, for Ti-modified catalysts, NiMoP/(x)Ti-SBA-15, the highest HDS activity was found when 15% of TiO2 was incorporated to SBA-15 and the catalyst was calcined at 773 K. This catalyst presented the highest TOF.

HDS and HDN activity of (Ni,Co)Mo binary and ternary nitrides prepared by decomposition of hexamethylenetetramine complexes

Highly dispersed pure phases of binary and ternary nitrides (Co,Ni)Mo were prepared using decomposition of hexamethylenetetramine (HMTA) complexes. Their catalytic activity was evaluated in the HDS of thiophene and HDN of quinoline. Three different pre-treatment modes were applied, including direct in situ preparation of nitrides in the catalytic reactor; pre-sulfidation with hydrogen sulfide and soft oxidation in air followed by sulfidation. Pure bimetallic nitrides are highly active HDN catalysts in the absence of sulfur and show substantial synergy effect between Ni or Co and Mo. By contrast, no synergy was observed for thiophene HDS, specific surface rates for binary and ternary nitrides being similar to that of unsupported MoS 2. Transmission microscopy, XRD and XPS studies showed that MoS 2 segregation on the surface occurs during HDS reaction or sulfidation with H 2S. As a result bimetallic catalysts contained nitride particles covered with MoS 2 layers and VIII group metal sulfide crystalline particles in the subsurface layer. The introduction in the preparation sequence of an additional step of oxidation–sulfidation led to a considerable increase of HDS catalytic activity of bimetallic catalysts. Pre-sulfidation of nitrides with H 2S/H 2 mixture resulted in a drastic decrease of specific surface area (Ssp) and very low HDS activity. Soft sulfidation with thiophene under reaction conditions led to high Ssp and high HDS activity per unit of mass.

Spectroscopic study of the electronic interactions in Ru/TiO 2 HDS catalysts

The characteristics of Ru/TiO 2 catalysts sulfided at temperatures from 573 to 873 K were studied by TPR-S, XRD, electron microscopy, EPR, and UV–Visible–NIR. It was found that the structure of the ruthenium sulfided phase formed at the different sulfidation temperatures is essentially the same when supported on alumina or titania. However, when supported on titania effects arising from electronic transfers between the Ru species and the TiO 2 support affect the performance of the catalyst. The high HDS activity of Ru/TiO 2 sulfided at 573 K was explained through the electronic interaction between metallic Ru (coming from the partial reduction of RuS 2) and titania. The low HDS activity of Ru/TiO 2 sulfided at 873 K was explained by the alteration of the already optimum electronic configuration of ruthenium sulfide caused by electron density supplied by the titania support. This provides experimental evidence to support the reported theoretical correlations between electronic structure and HDS activity.

Hydrodesulfurization properties of cobalt–nickel phosphide catalysts: Ni-rich materials are highly active

The HDS properties of a series of Co x Ni 2 − x P y /SiO 2 catalysts have been investigated as a function of the Co/Ni molar ratio (for a fixed P/Me molar ratio) and of the P/Me molar ratio (for a fixed Co/Ni molar ratio). An oxidic precursor composition of Co 0.08Ni 1.92P 2.00 on the silica support yielded the bimetallic phosphide phase having the highest HDS activity, 34% higher than that of an optimized nickel phosphide catalyst prepared from an oxidic precursor having a composition of Ni 2.00P 1.60. X-ray photoelectron spectroscopy revealed Ni-rich Co x Ni 2 − x P y /SiO 2 catalysts to have surface enrichment of P (relative to Ni 2.00P 1.60/SiO 2 and Co 2.00P 1.00/SiO 2 catalysts) and to incorporate remarkably low amounts of S during HDS testing. The high activity of these Co x Ni 2 − x P y /SiO 2 catalysts is attributed to surface enrichment of P relative to nickel phosphide, which results in improved resistance to S incorporation under HDS conditions. Consistent with these findings and the solid-state chemistry evidence that suggests that Ni atoms in Ni-rich Co x Ni 2 − x P y /SiO 2 catalysts occupy disproportionately more pyramidal M(2) sites than tetrahedral M(1) sites, we conclude that the high site densities of these catalysts are due to Ni atoms in surface M(2) sites, which results in P-enriched surfaces that are resistant to site blockage due to S incorporation.

Structure, stability and activity of RuS2 supported on alumina

The relationships between the structure attained by alumina-supported RuS2 during sulfidation, the extent of desulfurization of the sulfided phase during HDS, and the hydrodesulfurization activity of the catalyst were studied by TPS, TPR-S, XRD, FT-IR of CO, and DRS–UV–Vis–NIR. Sulfidation in H2S/N2 generates a mixture of RuS2-pyrite and RuS2-amorphous. As the sulfidation temperature increases, more RuS2-pyrite is produced at the expense of RuS2-amorphous. The later is not stable and undergoes reduction in reaction conditions, producing a sulfur-depleted catalyst (S/Ru<2) with low HDS activity. In contrast, RuS2-pyrite resists the drastic reducing conditions prevailing during HDS and is responsible for the high HDS activity. The changes in the catalyst properties with sulfidation temperature produce an opposite trend in the hydrogenation activity of naphthalene. The structure of the ruthenium sulfide catalyst can be tuned during sulfidation to achieve optimum performance according to the hydrodesulfurization or hydrogenation requirements of the reaction system.

Effect of the modified support γ-Al2O3-CaO on the structure and hydrodesulfurization activity of Mo and Ni-Mo catalysts

The effect of the support γ-Al2O3 modified with CaO by deposition–precipitation method on the structure, catalytic activity and selectivity of Mo and Ni-Mo catalysts for HDS was investigated. The resistance of the catalysts to deactivation by coke formation was also investigated. The samples have been characterized by means of XRD, DRS, XPS, Al27 NMR, TPR, and specific surface area and pore size distribution. The reaction of thiophene hydrodesulphurization, carried out at atmospheric pressure, was used as a model reaction for estimating the activity of the catalyst samples. The obtained results show that the applied method of modification with CaO leads to the formation of support with mesoporous structure and a considerable higher mechanical strength than that of the pure γ-Al2O3. Mo and Ni-Mo catalysts deposited on the modified support have higher HDS activity and resistance to coke formation. The presence of Ca2+ ions in the lattice of the support hinders the formation of crystallites of MoO3 and Al2(MoO4)3 phase. The higher catalytic activity of the samples with modified support is due to the higher degree of their sulfidation.

Reaction pathways on NiMo/Al 2O 3 catalysts for hydrodesulfurization of diesel fuel

The ranking of catalytic activities of several NiMo catalysts was performed using various model compounds: thiophene (TH), tetrahydrothiophene (ThTH), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). So-called type I and type II NiMo catalysts were prepared by varying Mo loading from below to above monolayer coverage. Type I and II differ most at high loading. Below monolayer surface coverage, type II active phase shows higher HG activity than type I. It is likely that type II active phase consists of higher stacking active phases, favoring the HG pathway. Consequently, type II catalyst shows higher HDS activity for TH and 4,6-DMDBT, as these sulfur compounds react mainly via HG pathway. Above monolayer surface coverage, type I active phase forms aggregated crystals on the support alumina, resulting in a low dispersion, whereas type II active phase can maintain high dispersion. Higher loading type I catalyst shows lower DDS activity and only slightly increased HG activity. Higher loading type II phase shows higher DDS and extremely high hydrogenation (HG) activity and, as a consequence, high HDS activity for TH and 4,6-DMDBT. In order to be able to generalize the results, we included a CoMo catalyst in the study. The results at first sight are not fully consistent. Although this catalyst shows a low HG activity in HDS of DBT, it shows a relatively high activity in HDS of 4,6-DMDBT. Two reaction schemes were examined, one of them taking into account a dehydrogenation step. Although a dehydrogenation step could occur under our experimental conditions, the main cause of ranking differences is the differences of susceptibility for NiMo and CoMo catalysts to H 2S.

TiO 2-supported iron–molybdenum hydrodesulfurization catalysts

TiO 2-supported Mo (6 and 12 wt.%) and Fe (0.25–1.0 wt.%) containing catalysts have been prepared using H 3PMo 12O 40 heteropolyacid (HPMo) and Fe salt of HPMo. Catalysts have been characterized by BET, SEM, IR, TPR, XPS methods and by their HDS activity in the reaction of thiophene conversion. Promoting effect of TiO 2 on Mo catalysts was confirmed, higher in case of catalysts with low Mo concentration (6 wt.%) than in case of the catalyst with 12 wt.% Mo. The highest HDS activity and stability was observed after introducing Fe in the form of HPMo countercation (Fe/Mo ∼ 0.1). Iron increases concentration of Mo 6+ and Mo 5+ in octahedral coordination. After sulfidation, the Fe-containing catalysts show presence of different Mo valence states (Mo 4+, Mo 5+, Mo 6+), Fe P, Mo P and/or Fe Mo P bonds that affect the HDS catalytic activity.

Optimum coating of USY as a support component of NiMoS on alumina for deep HDS of gas oil

Four types of alumina and/or USY-zeolite-supported NiMo catalysts (NMA, NMAZ, NMACZ1, NMACZ2) were examined in an autoclave for HDS of straight run gas oil (SRGO; S = 11,780 ppm) and its hydrodesulfurized gas oils (HSRGO; S = 340 ppm) to simulate a first and second layer catalyst. NMACZ1 and NMACZ2 were physical mixtures of alumina and surface modified USY-zeolites with different amounts of alumina, while NMAZ is a physical mixture of alumina and USY-zeolite. ACZ series catalysts were prepared to obtain high HDS activity of NiMo on zeolite-containing supports without extensive cracking of hydrocarbons. USY-zeolite in NMACZ1 was coated with more alumina than that in NMACZ2, which showed the highest HDS activity in the first and second layers, achieving 34 ppm sulfur (ppm S) for the first layer and almost complete removal of sulfur species in the second layer at 340 °C. NMAZ showed high HDS activity for both layers. NMACZ1 showed medium HDS activity for the first layer, but very high HDS activity for refractory sulfur species in the second layer. A large amount of light hydrocarbons were produced over NMAZ through cracking of heavy hydrocatbon, while NMACZ1 and NMACZ2 produced lower amounts of light hydrocarbons, reflecting the greater amount of coating alumina. It must be noted that lower reaction temperatures of 330 and 320 °C achieved almost completely 0 ppm in the second layer, where the hydrocracking was very low level. Their clearly defined HDS activities against each layer may be due to the differences of MoS 2 structures, support acidities and their surface areas, which are in turn due to morphologies of their supports.

Thiophene hydrodesulfurization over alumina-supported β-Mo 2N 0.78 catalyst

Alumina supported β-Mo 2N 0.78 catalyst was synthesized via temperature programmed reaction in the N 2–H 2 mixture gases. Catalyst properties were also investigated by X-ray diffraction (XRD), BET surface area and temperature programmed reduction (TPR) methods. The HDS activity of the catalyst was measured under different Mo loading. The HDS results indicated that there was a suitable Mo loading of β-Mo 2N 0.78/γ-Al 2O 3 catalyst with high HDS activity. The TPR result suggested that sulfur replaced the surface oxygen of the passivated catalyst in the HDS reaction.

Urea–organic matrix method: an alternative approach to prepare CoMoS2/γ-Al2O3 HDS catalyst

An alternative method using urea as organic matrix to prepare CoMoS2/γ-Al2O3 HDS catalysts based on drying (urea-matrix drying, UMxD) or combustion (urea-matrix combustion, UMxC) processes have been developed and compared with the traditional wet methods (sequential, WSI, and co-impregnation, WCI) and chelating method (ChM) in order to determine their influence on the HDS catalytic process. The catalytic performance of the alumina-supported CoMo catalysts was evaluated in a continuous flow reactor using the hydrodesulfurization of thiophene as a model reaction. The oxidic precursors and the sulfurized catalysts were characterized using elemental analysis, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR-H2) and BET surface area measurements. It has been found that the urea–organic matrix method facilitates well-dispersed Co- and Mo-oxo species (mono and polymolybdate) formation, whereas the conventional impregnation techniques lead to mixed-metal oxides formation. This was reflected in the sulfurized phase morphology and structural disorder degree of carbon material deposited on the catalyst surface upon the sulfurizing process using thiophene as sulfurizing agent. The preparation method notably affects the thiophene-HDS specific rates, showing the following activity order: UMxD>UMxC>WCI>WSI>ChM, while an opposite trend for relative rate of HYD to HDS reactions was observed. A carbon structural effect together with high stacking degree of the sulfurized phases seem to be mainly responsible for the high HDS activity of alumina-supported CoMo catalysts prepared by the urea–organic matrix method, which appears very promising for HDS catalysts development.

Hydrodesulfurization of Dibenzothiophene over Cobalt−Molybdenum Nitride Catalysts

Molybdenum nitride (γ-Mo 2 N) and Co-promoted molybdenum nitrides (Co-Mo-N) catalysts with high surface area have been prepared from the reaction of MoO 3 and Co-Mo oxides with N 2 -H 2 and characterized by XRD and BET. The results of measurement of hydrodesulfurization-(HDS) of dibenzothiophene(DBT) supported the following conclusions: (1) γ-Mo 2 N and Co-Mo-N have higher HDS activity and selectivity for C-S bond breakage in dibenzothiophene; (2) different pretreatment conditions affect the HDS activity and selectivity; (3) the HDS activity of the γ-Mo 2 N is significantly improved with the addition of a Co promoter.

A refinement on the notion of type i and II (Co)MoS phases in hydrotreating catalysts

The influence of Mo content on thiophene hydrodesulfurization for alumina- and carbon-supported (Co)Mo catalysts is investigated by TPR, XPS and H2-D2 equilibration. Activity trends for alumina-supported catalysts are explained by a gradual change of the type I MoS2 active phase from a large to a small number of Mo-O-Al anchors. A pure type II phase without such anchors and a high HDS activity is only obtained employing chelating ligands or a carbon support. At low Mo loading a separate oxysulfidic Mo species in strong interaction with alumina exhibits an unexpectedly high HDS activity, which, however, is difficult to promote by Co.

Thiophene hydrodesulfurization on sulfided Ni, W and NiW/USY zeolite catalysts: effect of the preparation method

The effect of the preparation method and metal loading on the hydrodesulfurization ⊙HDS) of thiophene, and on the dispersion and location of Ni and/or W species in Ni, W and NiW sulfides supported on USY zeolite, was investigated by temperature-programmed reduction ⊙TPR), X-ray photoelectron spectroscopy, N 2adsorption and acidity determination. The monometallic Ni catalyst prepared by ion exchange [Ni ⊙int)] exhibited higher initial HDS activity than those prepared by impregnation [Ni ⊙imp)] and by ion exchange and subsequent formation of small NiO clusters by NaOH treatment [Ni ⊙clus)]. For the binary NiW catalyst series with different metal contents, the catalysts prepared by impregnating W onto the Ni ⊙int) one showed activities comparable to those of the catalysts prepared by impregnating Ni onto the W/USY sample. These catalyst series showed much higher activities than those prepared by impregnating W onto the Ni ⊙clus). The characterization results revealed that catalysts displayed significant differences in dispersion, location and sulfidation of the Ni and W phases dependent on the preparation method. However, none of these factors alone accounted for the activity trend. In general, it was found that a combination of high acidity and metal dispersion led to catalysts with high initial HDS activity.