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%.

Influence of precursor compounds on the structural and catalytic properties of CoNiMo/SBA-15 catalysts used in the hydrodesulfurization of dibenzothiophene

In the present research project, it was studied in detail how the incorporation of different precursor compounds and the supplementary addition of amounts of nickel in the MoS2 slabs can influence the structural and catalytic properties of trimetallic CoNiMo catalysts supported on SBA-15 mesoporous support with precise control of the amount and nature of the promoters. The catalysts were prepared by the incipient impregnation method using ammonium heptamolybdate and cobalt and nickel acetate, and nitrate as precursors adding nickel in molar amounts (5, 10, and 20%) of the cobalt atomic loading. Adding the Ni in small amounts allows us to keep the (Co + Ni)/(Co+Ni+Mo) molar ratio near 0.3. The catalysts formed were labeled according to the precursor compounds used (CoNixMo-Ac for acetates and CoNixMo-N for nitrates), where x is the percentage of nickel. Catalysts were then characterized by N2 adsorption-desorption isotherms, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalysts were tested in the HDS of dibenzothiophene (DBT).Results show a significant impact of adding small amounts of nickel and the type of precursor compounds used for the CoNiMo trimetallic catalysts on the final HDS activity. In the case of the catalysts prepared with cobalt and nickel acetates, it was observed that the initial reaction rate values increased as the amount of Ni increased, being the CoNi5Mo-Ac, the catalyst with the lower catalytic activity. Increasing the amount of Ni causes an increase in the HDS of DBT. In the case of the catalysts prepared with nitrates, it could be observed a similar effect. The catalyst with the higher catalytic activity in both series was the CoNi20Mo-Ac. These results agree with the TEM analysis in which a decrease in the slab length of the MoS2 could be regarded as the de Ni amount increase. This means that the type of precursor used has an essential effect on the catalysts since modify their properties and catalytic activity and suggests that the materials synthesized with acetate precursors can help to improve the intrinsic activity of the HDS sites.

Unblocking of NiMo Active Sites for Hydrodesulfurization Catalysts: A Study Focused on Inactive NixSy Segregation

The formation of NixSy/CoxSy phases on the HDS catalyst surface during catalyst preparation poses the following challenges in the HDS reaction: (1) inactive in the reaction, (2) hinder the role of promoters, (3) block the actives sites (NiMoS/CoMoS) at the perimeter, and (4) increase the inert mass on the catalyst surface. Since the formation of NixSy/CoxSy phases is thermodynamically favorable, it is difficult to control this during the catalyst synthesis. In this regard, this work investigates the effect of metal-support interactions and catalyst compositions on NixSy phase separation and removal of NixSy phases from the catalyst surface using acid-leaching method. The HDS activity for NiMo supported on amorphous alumina (NiMo/A-Al2O3) catalysts significantly increased after the acid-leaching treatment by unblocking the active NiMoS sites and increasing the Ni-MoS2 interaction through alumina support leaching. Overall, the HDS activity for leached NiMo/A-Al2O3 catalysts is 25–30% higher than that for conventional NiMo/γ-Al2O3 catalysts.

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.

Synthesis and characterization of lanthanum-modified pseudoboehmite - The precursor of alumina supports and catalysts

The present work shows that the introduction of 0.25–1.25 wt% lanthanum to the composition of aluminum hydroxide at the stage of its hydrothermal synthesis allows increasing the content of the pseudoboehmite phase in the product up to 95 wt% and, as a consequence, reduces the content of the “amorphous” component. Lanthanum uniformly distributes over the surface of aluminum hydroxide as isolated cations with a surface density of 10–15 cations per 10 nm 2 . During plasticizing of lanthanum-modified pseudoboehmite followed by granulation and heat treatment, the formation of the oxide form of La is not observed, and the cations retain their isolated state. The specific surface area of La-modified alumina increases by 18–26 m 2 /g compared to the unmodified sample, while the pore volume remains the same and the average pore diameter slightly reduces. It was found that when the content of La in pseudoboehmite was 1 wt%, the temperature of reaching a residual sulfur content of 10 ppm in the hydrotreated diesel fuel was 5 °C lower comparing to the unmodified sample. • The effect of La addition at the stage of pseudoboehmite preparation was studied. • La promotes the formation of pseudoboehmite phase. • La is present as isolated cations on the surface of pseudoboehmite and alumina. • Catalyst with 1 wt% La shows the highest HDS and HDN activity.

Electron transfer behaviour of ternary Fe-Zn-F active phase and its enhancement of hydrodesulfurization activity of DBT

In this work, a ternary hydrodesulfurization catalyst with fluorine introduced into the FeZn bimetallic active sites was prepared by a step-by-step incipient wetness impregnation. Among them, the sulfur removal ability increases gradually with the addition of F, and then tends to remain constant. Compared with FeZn catalyst, the maximum activity of the fluorinated catalyst can increase to 6 times at 613 K. It is found that the synergy effect exists in the ternary FeZnF species according to the characterization results. As a part of the active phase, not only the acidity of the catalyst was improved and the dispersion of metal species was optimized by F, but also the closed cycle of complex electron transfer among Fe-Zn-F was aggravated resulting in the weaken of Fe-O/Fe-S bond. Therefore, the sulfurization degree of FeZnF(x) was improved which leads to more active sites and noteworthy HDS activity.

Synthesis and Characterization of NiMo Catalysts Supported on Fine Carbon Particles for Hydrotreating: Effects of Metal Loadings in Catalyst Formulation

The by-products collected during the synthesis of carbon nanohorns via the arc discharge synthesis method is comprised of other carbon particles (OCP). At a hydrotreating operating temperature of 370°C, preliminary investigations using a bimetallic catalyst with support originating from the fine fractions of other carbon particles (OCPf) and containing 13 wt% Mo and 2.5 wt% Ni resulted in an HDS and HDN conversion of 78 and 25%, respectively. Variation of metal compositions in catalyst formulation and its impact on hydrotreating activity was therefore considered in this study to enhance the hydrotreating activity of OCPf–supported catalyst, and to determine if the best NiMo/OCPf catalyst achieved from this study could be a viable catalyst for hydrotreating applications. The co-incipient wetness impregnation was used in preparing series of hydrotreating catalysts with Ni and Mo loadings within the range of (2.5–5.0 wt%) and (13–26 wt%) respectively. Overall, the catalyst samples with maximum Ni loading of 5.0 wt% and Mo loadings of either 13 or 19 wt% showed higher dispersion and the ability to form a Type II Ni-Mo-S phase with enhanced activity. The effects of metal compositions on both HDS and HDN activities were correlated with their physicochemical properties.

On the contribution of the cobalt sulfide phase to the global activity of industrial-type CoMo/Al2O3 catalysts in the HDS of DBT

To analyze if the HDS activity is the result of contributions of both CoMoS and cobalt sulfides phases, a series of CoMo/Al2O3 catalysts with increasing Co/(Co+Mo) ratios (r = 0.1, 0.2, 0.3 and 0.4) prepared by simultaneous impregnation, and composites formed with the CoMo/Al2O3 catalysts and Co/Al2O3, were tested in the hydrodesulfurization of dibenzothiophene. The catalysts were characterized by UV–Visible–NIR and infrared of adsorbed CO spectroscopies. The results showed that the amount of CoMoS adsorbing sites remains basically the same in the series of promoted catalysts, while an increase of the precursor of cobalt sulfide is observed. The activity experiments showed that the addition of Co/Al2O3 to Mo/Al2O3 or CoMo/Al2O3 catalysts promotes both the MoS2 and CoMoS phases, and that the rate constants of CoMo/Al2O3 r = 0.2 and CoMo/Al2O3 r = 0.3 can be closely reproduced with composites of CoMo/Al2O3 r = 0.1 with different amounts of Co/Al2O3, indicating that the increased activity in the series of Co-promoted catalysts is related to the presence of cobalt sulfide. It was evidenced that Co-promoted catalysts are complex systems in which several surface species contribute to the global hydrodesulfurization activity and that cobalt sulfide, far from being a spectator in HDS catalysis, has in fact a secondary but significant role in the global performance of industrial-type CoMo/Al2O3 hydrodesulfurization catalysts. All these contributions must be optimized to obtain highly active and selective hydrodesulfurization catalysts.

Ultradispersed (Co)Mo catalysts with high hydrodesulfurization activity

In spite of the huge worldwide interest for single-atom and ultradispersed catalysts, metal atoms coordinated with sulfur are rarely addressed. In this work, ultradispersed molybdenum-based catalysts were obtained by adsorption of three thiomolybdates of different nuclearity (n = 1, 2, 3) on high-surface-area S-doped carbon, followed by sulfidation in H2S/H2 flow at 350 °C. Scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) attest that single atoms and few-atom clusters are predominant on the surface of the materials after adsorption, as well as after sulfidation and thiophene HDS reaction. Independently on the nature of the thiomolybdate precursor, sulfidation leads to catalysts with specific thiophene HDS activity exceeding that of a conventional supported MoS2 reference. Ultradispersed clusters were further promoted with cobalt, yielding HDS turnover frequencies 2–3 times higher than those of reported benchmark CoMoS catalysts. These findings provide new insights into the previously debated issues of structure-activity relationships for HDS catalysts and expand the range of applications of atomically dispersed catalysts.

A hierarchical ZSM-22/PHTS composite material and its hydro-isomerization performance in hydro-upgrading of gasoline

The ZSM-22/PHTS (ZP) composite material assembled from a ZSM-22 zeolite crystal displayed a mesoporous structure. The CoMo/ZPA120 catalyst presented a good balance between HDS activity (95.2%) and lower ΔRON (−1.1).

Characterization and HDS Activity of Mo and NiMo Sulfided Catalyst Prepared by Thioglycolic Acid Assisted Hydrothermal Deposition Method

Characterization and HDS Activity of Mo and NiMo Sulfided Catalyst Prepared by Thioglycolic Acid Assisted Hydrothermal Deposition Method

New approach to unsupported ReS2 nanorod catalyst for upgrading of heavy crude oil using methane as hydrogen source

Highly active ReS2 nanocatalysts were prepared by CVD method and characterized by XRD, BET -BJH, Raman spectroscopy, XPS, TPR, NH3-TPD, SEM, and HRTEM techniques. Catalytic activities were used in upgrading heavy crude oil using methane as hydrogen source. The results showed a significant increase in API and decrease in sulfur and nitrogen content of crude oil. RSM technique was used to investigate the interactive effects of temperature (200–400 °C), pressure (20–40 bar) and dosage of nanocatalyst (0.5–2 wt. %) on the performance of HDS reaction. The results represent that the maximum predicted HDS activity (74.375%) was estimated under the optimal conditions (400 °C, 20 bars, and 2 wt % of nanocatalyst). Also, the effect of reaction temperature, pressure and dosage of ReS2 nanorods catalyst on HDN of heavy crude oil was investigated and highest efficiency in the HDN process (93%) occurred at 400 °C and 40 bar using 2 wt % ReS2.

Enhanced catalytic activity of ultrasmall NiMoW trimetallic nanocatalyst for hydrodesulfurization of fuels

As the need of the hour, it is imperative to develop highly active HDS catalyst capable of desulfurizing refractory organic sulfur compounds (DBT; 4, 6 DMDBT etc.). In comparison to well established bimetallic catalysts (e.g. NiMo/NiW), trimetallic catalysts exhibit synergistic effect between active metal species which promotes both direct desulfurization (DDS) and hydrogenation pathway (HYD) and hence display higher catalytic activity. The synergistic effect is determined by the catalytically active amorphous phase formed due to partial substitution of Mo by W during synthesis of trimetallic nanocatalysts. This can be achieved by synthesizing the catalyst as ultrasmall size nanocatalysts. To this end, in the present study we report NiMoW trimetallic nanocatalysts preparation procedure using colloidal synthesis technique. For the sake of better comparison, Ni/(Ni + Mo + W) molar ratio for all the investigated catalysts (bimetallic and trimetallic) was kept the same (~0.28 ± 0.03). For the hydrodesulfurization of dibenzothiophene (DBT), because of improved synergistic effect, trimetallic NiMoW/γ-Al2O3 showed ~ 36% higher conversion in comparison to NiMo/ γ-Al2O3 and ~ 21% higher DBT conversion in comparison to NiW/ γ-Al2O3 catalyst. The catalytic activity of synthesized nanocatalysts was compared with catalyst prepared using well established metal impregnation method. Improved catalytic activity in case of synthesized NiMoW nanoclusters is attributed to the controlled partial substitution of Mo by W during the colloidal synthesis which enhances the synergistic effect.

Pt-confinement catalyst with dendritic hierarchical pores on excellent sulfur-resistance for hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Metal confinement catalyst MoS2/Pt@TD-6%Ti (TD, TS-1/Dendritic mesoporous silica nanoparticles composite) in dendritic hierarchical pore structures was synthesized and showed excellent sulfur-resistance performance and stabilities in catalytic hydrodesulfurization reactions of probe sulfide molecules. The MoS2/Pt@TD-6%Ti catalyst combines the concepts of Pt-confinement effect and hydrogen spillover of Pt noble metal. The modified micropores of Mo/Pt@TD-6%Ti only allow the migration and dissociation of small H2 molecules (0.289 nm), and effectively keep the sulfur-containing compounds (e.g. H2S, 0.362 nm) outside. Thus, the MoS2/Pt@TD-6%Ti catalyst exhibits higher DBT and 4,6-DMDBT HDS activities because of the synergistic effect of the strong H2 dissociation ability of Pt and desulfurization ability of MoS2 with a lower catalyst cost. This new concept combining H2 dissociation performance of noble metal catalyst with the desulfurization ability of transition metal sulfide MoS2 can protect the noble metal catalyst avoiding deactivation and poison, and finally guarantee the higher activities for DBT and 4,6-DMDBT HDS.

Enhanced HDS and HYD activity of sulfide Co-PMo catalyst supported on alumina and structured mesoporous silica composite

Co-PMo catalysts were prepared from the 12-molybdophosphoric heteropolyacid and cobalt citrate on the base of freshly-synthesized alumina and mixed MCM-41-Al2O3 material. Carriers and catalysts were characterized by the following techniques: X-ray powder diffraction, low-temperature N2 adsorption, NH3-TPD, Raman spectroscopy, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Prepared catalysts were tested in hydrodesulfurization of dibenzothiophene and hydrogenation of naphthalene. It has been shown that mesoporous silica incorporation into alumina can improve morphological properties of the CoMoS active phase as well as the overall HDT activity.

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.

Effects of pore size, mesostructure and aluminum modification on FDU-12 supported NiMo catalysts for hydrodesulfurization

A series of NiMo/FDU-12 catalysts with tunable pore diameters and mesostructures have been controllably synthesized by adjusting the synthetic hydrothermal temperature and applied for the hydrodesulfurization of dibenzothiophene and its derivative. The state-of-the-art electron tomography revealed that the pore sizes of FDU-12 supports were enlarged with the increase in the hydrothermal temperature and the mesostructures were transformed from ordered cage-type pores to locally disordered channels. Meanwhile, the MoS2 morphology altered from small straight bar to semibending arc to spherical shape and finally to larger straight bar with the change of support structures. Among them, FDU-12 hydrothermally treated at 150 °C possessed appropriate pore diameter and connected pore structure and was favorable for the formation of highly active MoS2 with curved morphology; thus, its corresponding catalyst exhibited the best HDS activity. Furthermore, it was indicated that the isomerization pathway could be significantly improved for HDS of 4,6-dimethyldibenzothiophene after the addition of aluminum, which was expected to be applied to the removal of the macromolecular sulfur compounds. Our study sheds lights on the relationship between support effect, active sites morphology and HDS performance, and also provides a guidance for the development of highly active HDS catalysts.

Modified Dendritic Mesoporous Silica Nanospheres Composites: Superior Pore Structure and Acidity for Enhanced Hydrodesulfurization Performance of Dibenzothiophene

Dendritic mesoporous silica nanospheres (DMSNs) with a center-radical pore structure were successfully fabricated with ZSM-5 seeds to synthesize hierarchically meso–microporous ZSM-5/DMSN (ZD) materials which were used as the support for preparing HDS catalysts. The catalytic activities were evaluated by adopting DBT as the model oil. ZD composites and the corresponding catalysts were well characterized by XRD, XPS, HRTEM, and other techniques. The characterization results manifested that the specific center-radical pore structure was retained after incorporation of microporous zeolite ZSM-5; thus, ZD exhibited a wide pore diameter of about 17 nm, which was definitely preferable for mass transfer in the S removal process. Meanwhile, the open pore channels enhanced the accessibility of the active sites on the internal surface of the catalysts. Introducing ZSM-5 seeds into the framework of DMSNs also improved the acidity and modulated the metal–support interaction as well. As a result, NiMo/ZD series catalysts demonstrated high HDS activities, of which NiMo/ZD-3 achieved the highest HDS efficiency of 98.3%. The superior catalytic performance not only originated from the large center-radical pore structure and good acidity of support but also related to the suitable metal–support interaction and perfect dispersion of the metallic active sites.

Peptization of alumina by ammonia to adjust catalytic properties of NiMo/B-Al2O3 hydrotreating catalysts

NiMo/B-Al2O3 catalysts for VGO hydrotreating differed in peptizing agent for supports preparation (nitric acid or ammonium solution) have been studied. The molar ratio of HNO3/Al2O3 = 0.03 and NH3aqua/Al2O3 = 0.09 and 0.15 were used. Supports and catalysts were studied by the nitrogen and mercury adsorption, IR-spectroscopy of adsorbed CO, XRD, 11B and 27Al NMR, UV–vis DRS, HRTEM, XPS. NiMo/B-Al2O3 catalyst peptized by ammonia at molar ratio of NH3/Al2O3 = 0.09 contains higher amount of NiMoS phase than catalysts peptized by nitric acid. Boron catalyst based support peptized by nitric acid is characterized by active component particles with lower slab length. Simultaneous presence of ammonia and boron results in increase of the slab length of active component, while stacking number decreases. According to the results of catalytic testing in HDS of DBT, boron-containing catalysts are more active. However, NiMo/B-Al2O3 catalyst obtained using ammonia with molar ratio of NH3/Al2O3 = 0.09 has higher activity in HDS of DBT in comparison with NiMo/B-Al2O3 catalyst obtained using nitric acid. Testing in VGO hydrotreating confirmed that utilization of ammonia as a peptizing agent for support preparation significantly improves the activity of boron catalyst in HDS and HDN reactions.

NiMo Catalysts Supported on Al-Based Mixed Oxide Prepared By Hydrothermal Method: Effect of Zn/Al Ratio and Addition of Silica on HDS Activity

The effect of Zn/Al ratio and addition of silica to Al–Znx oxides on the structure and catalytic properties of supported NiMo catalysts in hydrodesulfurization reaction of thiophene was studied. NiMo catalysts were synthesized by simultaneous impregnation of Ni acetate and 12-molybdophosphoric acid on Al–Znx and Al–Zn0.16–Si mixed oxide (with x = Zn/Al ratio of 0.05–0.57) prepared by hydrothermal synthesis at 180 °C. Colloidal SiO2 was added to the Al–Znx oxides (Si/Al = 0.3 ratio) to modify textural and structural properties of NiMo catalysts. These materials were characterized by N2 physisorption, SEM, XRD, FTIR, UV–Vis DRS, TPR–H2, TPD–NH3, XPS, HRTEM and tested in thiophene conversion at 280–400 °C and 1.0 MPa. It was found out that the surface area of the supports calcined at 500 °C, decreases with the increasing Zn/Al ratio, which could be due to the interaction of the Zn with the alumina, leading to formation of Zn-spinel. After impregnation of the supports with NiMo active components, the presence of Zn increases the amount of surface Mo in octahedral sites at Zn/Al = 0.21 ratio. At this ratio maximum in HDS activity of NiMo/Al–Znx samples was observed. Addition of silica to Al-Zn mixed oxide (Zn/Al = 0.16) leads to more active NiMo catalyst due to formation of more Ni(Zn)–Mo–S active species as revealed by XRD and HRTEM.