Hydrodesulfurization Of Dibenzothiophene Research Articles

Preparation of Ni2P with a Surface Nickel Phosphosulfide Layer by Reduction of Mixtures of Na4P2S6 and NiCl2

AbstractA series of physical mixtures of Na4P2S6 and NiCl2 (P‐NiPS(x), where x represents the P/Ni molar ratio) were employed for the preparation of Ni2P. For comparison, a sulfur‐containing Ni2P catalyst (Ni2P‐S) and a sulfur‐free Ni2P catalyst (Ni2P‐TPR) were prepared by reduction of Ni2P2S6 and a nickel phosphate precursor, respectively. The reduction of the P‐NiPS(x) precursors with P/Ni ratios above 2/3 yielded Ni2P catalysts with a distinct nickel phosphosulfide layer (NiPS(x)), and the Ni2P phase started to form at ca. 200 °C. The reduction of Ni2P2S6 to Ni2P most likely follows a disproportionation mechanism. The P3+ species in Ni2P2S6 disproportionate to PH3 and P5+ during the reduction, and PH3 further reacts with nickel and sulfur species to form Ni2P and the surface nickel phosphosulfide layer. The sulfur atoms in the nickel phosphosulfide phase were in the form of S2−. The introduction of sulfur to Ni2P favored the hydrogenation pathway of the hydrodesulfurization (HDS) of dibenzothiophene (DBT), but hardly affected the direct desulfurization (DDS) pathway and inhibited the hydrogenation of biphenyl. The DDS pathway rate constants of DBT HDS over the Ni2P‐TPR and NiPS(x) catalysts were observed to increase linearly with the increase in their surface Ni atomic concentrations.

Interplay Between Ni and Brønsted and Lewis Acid Sites in the Hydrodesulfurization of Dibenzothiophene.

Ni-MoS2/γ-Al2O3 catalysts are commonly used in hydrotreating to enhance fossil fuel quality. The extensive research on these catalysts reveals a gap in understanding the role of Ni, often underestimated as an inactive sulfide phase or just a MoS2 promoter. In this work, we focused on analyzing whether well-dispersed supported nickel nanoparticles can be active in the hydrodesulfurization of dibenzothiophene. We dispersed Ni by Strong Electrostatic Adsorption (SEA) method across four supports with different types of acidity: silica (~ neutral acidity), γ-Al2O3 (Lewis acidity), H+-Y zeolite, and microporous-mesoporous H+-Y zeolite (both with Brønsted-Lewis acidity). Our findings reveal that Ni is indeed active in dibenzothiophene hydrodesulfurization, even with alumina and silica as supports, although their catalytic activity declines abruptly in the first hours. Contrastingly, the acid nature of zeolites imparts sustained stability and performance, attributed to robust metal-support interactions. The efficacy of the SEA method and the added mesoporosity in zeolites further amplify catalytic efficiency. Overall, we demonstrate that Ni nanoparticles may perform as a hydrogenating metal in the same manner as noble metals such as Pt and Pd perform in hydrodesulfurization. We discuss some of the probable reasons for such performance and remark on the role of Ni in hydrotreatment.

Comparison of the HDS DBT reaction using bulk and supported catalysts

The paper describes in detail the procedure for the preparation of a granular bulk NiMoW catalyst and a supported reference NiMo/Al2O3 catalyst. Mention is made of investigations of the supported and bulk catalysts by various physico-chemical methods (nitrogen adsorption-desorption method, X-ray photoelectron spectroscopy, TPD-NH3, HRTEM and X-ray diffraction analysis). The experiments to estimate catalytic activity and compare rate constant of hydrodesulfurization of dibenzothiophene using both catalysts have been carried out. It is shown that textural properties of the catalysts significantly differ. The supported catalyst has more developed specific surface area and pore volume than the bulk catalyst. TPD-NH3 showed an increased acidity of the supported catalyst in comparison the bulk catalyst. It is shown by the X-ray photoelectron spectroscopy method that in both samples Mo on the surface is present exclusively in the form of Mo4+ ion. However, the bulk catalyst differs from the supported catalyst in that it contains a larger amount of Ni as part of the active NiMo(W)S phase. The catalytic activity tests demonstrated that the bulk catalyst is more active at 240, 250 and 260°C, it is discovered that the rate constant in hydrodesulfurization of dibenzothiophene for the bulk NiMoW catalyst is twice higher at 240ºC than that of the supported NiMo/Al2O3 catalyst.

MOF-derived CoP/C catalyst for efficient dibenzothiophene hydrodesulfurization

The design of an active and sulfur-resistant catalyst for dibenzothiophene (DBT) hydrodesulfurization (HDS) in crude oil purification is highly desirable but remains a grand challenge. Here, two carbon-supported cobalt phosphide catalysts Co2P/C and CoP/C, and a reference sample Co/C are successfully synthesized using a metal–organic-frameworks (MOFs) precursor. A P/Co ratio dependence on crystal phases is found, leading to the formation of two pure-phase cobalt phosphide catalysts CoP/C and Co2P/C. Catalyst evaluation in HDS of DBT shows that the CoP/C catalyst exhibits a higher activity and stability than Co2P/C and Co/C, giving a 93.7 % DBT conversion with 100 h stability under 3 MPa and 380 ◦C. Moreover, a 67.4 % biphenyl yield characterizes the dominance of the direct desulfurization (DDS) pathway. The obtained catalytic performance over the CoP/C catalyst is also superior to the published cobalt phosphide catalysts. Multiple characterization techniques co-evidence that the copious specific surface area, efficient electron transport from Co to P, high thermal stability of Co nanoparticles (NPs), and strong sulfur resistance account for the enhanced catalytic performance of CoP/C. The findings of this report suggest that phosphorus-modified cobalt over the carbon support can act as a promising catalyst for the HDS of DBT.

Effects of Pyrolyzing and Phosphiding on Dibenzothiophene Hydrodesulfurization of MOF-Derived Ni2P

Effects of Pyrolyzing and Phosphiding on Dibenzothiophene Hydrodesulfurization of MOF-Derived Ni2P

Hydrodesulfurization of Dibenzothiophene: A Machine Learning Approach.

The hydrodesulfurization (HDS) process is widely used in the industry to eliminate sulfur compounds from fuels. However, removing dibenzothiophene (DBT) and its derivatives is a challenge. Here, the key aspects that affect the efficiency of catalysts in the HDS of DBT were investigated using machine learning (ML) algorithms. The conversion of DBT and selectivity was estimated by applying Lasso, Ridge, and Random Forest regression techniques. For the estimation of conversion of DBT, Random Forest and Lasso offer adequate predictions. At the same time, regularized regressions have similar outcomes, which are suitable for selectivity estimations. According to the regression coefficient, the structural parameters are essential predictors for selectivity, highlighting the pore size, and slab length. These properties can connect with aspects like the availability of active sites. The insights gained through ML techniques about the HDS catalysts agree with the interpretations of previous experimental reports.

Synthesis and Characterization of NiMoS/TiMg and NiWS/TiMg Nanocatalysts and Their Application in the Hydrodesulfurization of Dibenzothiophene

Synthesis and Characterization of NiMoS/TiMg and NiWS/TiMg Nanocatalysts and Their Application in the Hydrodesulfurization of Dibenzothiophene

Sulfured NiMo catalysts on TiO2-Nb2O5 nanocomposites for efficient hydrodesulfurization performance

The implementation of increasingly stringent environmental regulations has increased the demand for more active catalysts in hydrotreating. This study proposes the synthesis, characterization, and evaluation of bimetallic NiMo catalysts supported on TiO2-Nb2O5 nanocomposites for dibenzothiophene hydrodesulfurization. Samples containing 3, 5, and 10 wt% Nb2O5 were synthesized to examine the influence of Nb content on their catalytic activity and selectivity. Supports and oxidized catalysts were characterized using various techniques, including SEM-EDS, N2 physisorption, powder XRD, UV–vis DRS, Raman spectroscopy, and H2-TPR, while sulfured catalysts were further characterized by XPS and HRTEM. NiMo/TiNb3 and NiMo/TiNb5 catalysts displayed propene and diisopropyl ether as the main products in the 2-propanol dehydration reaction. A correlation was observed between hydrogenating capabilities in the HDS and dehydration tests with the Nb loading, suggesting that an optimal combination of Lewis/Brønsted acid sites enhances the BP/CHB ratio. All Nb-containing samples exhibited superior activity compared to their Nb-free counterparts, as indicated by the higher values of the pseudo-first-order rate constants (kHDS), which were higher for the NiMo/TiNb3 catalyst. These results were also associated with the respective textural characteristics, metal dispersion, and species distribution.

Synergistic effect between CoSx and MoS2 at the micrometer scale: Considerable promotion of the hydrodesulfurization of DBT

The future implementation of ultralow sulfur fuel regulations requires researchers to have an excellent understanding of the mechanism of the synergistic effect between the Co(Ni) and (Mo)W sulfides in supported Co(Ni)Mo(W)S hydrodesulfurization (HDS) catalysts. This synergistic effect occurs when the distance between two metals is on the mm or nm scale. To investigate the promotion of HDS on the µm scale, a series of Co and Mo multilayer flake catalysts with a thickness of 1 mm were prepared by laminate molding. The distance between CoSx and MoS2 in these specially structured catalysts was adjustable on the µm scale by controlling the order and quality of the catalyst powder. The results for the HDS of dibenzothiophene (DBT) demonstrate that there is an obvious synergistic effect between CoSx and MoS2 on the µm scale. The results of pyridine IR spectroscopy indicate that this synergy is due to CoSx and MoS2 synergistically generating more coordinatively unsaturated sites (CUSs) and -SH active sites at the μm scale, thus increasing the HDS activity. Moreover, the catalyst activity increases as the distance between CoSx and MoS2 decreases, and the fact that the feed comes into contact with CoSx first greatly improves the activity.

Hierarchically porous ZSM-5/SBA-15 composite: Tuning pore structure and acidity for hydrodesulfurization of dibenzothiophene

Series ZSM-5/SBA-15 (ZS15-x) composites with different pore structure and acidity were synthesized, and the corresponding NiMo/ZS15-x catalysts were prepared for dibenzothiophene (DBT) hydrodesulfurization (HDS). The controlled introduction of ZSM-5 nanocrystal imparts more acid sites to the NiMo/ZS15 catalyst without altering its fundamental morphology. Furthermore, the increased presence of acid sites enhances the HDS effect of NiMo/ZS15-x catalysts. Simultaneously, the introduction of ZSM-5 nanocrystal modulates the interactions between metal and support (MSI), thereby promoting the dispersion of the active sites. The optimized NiMo/ZS15-50 exhibited superior HDS activities of 98.9 % for DBT, with the optimal reaction rate constant of 3.0 × 10−7 mol/g s−1 and turnover frequency of 2.0 × 10−4 s−1. This can be attributed to its two-dimensional open channels, suitable acidic sites and highly dispersed MoS2. The increased proportion of the ZSM-5 framework and enhanced acidity are advantageous for DBT HDS.

Monodisperse dendritic micro-mesoporous composite self-assembled with tiny TS-1 seeds as efficient catalysts for hydrodesulfurization of dibenzothiophenes

Novel TS-1/dendritic mesoporous silica nanoparticles (TS-1/DMSNs, TD) micro-mesoporous composites with different morphology were prepared for NiMo catalysts (NiMo/TD-TEA). Series catalysts were tested in dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) reactions in a fix-bed reactor. TS-1 were uniformly compounded with mesoporous materials in the form of Si-O-Ti bonds, which did not affect the typical dendritic morphology. The introduction of TEA could inhibit the growth of support particles, and modulate the acidity and the metal-support interaction (MSI) of catalysts. Optimized NiMo/TD-TEA catalyst showed the optimal DBT (98.0 %) and 4,6-DMDBT (92.3 %) desulfurization rate as well as the excellent hydrogenation (HYD) selectivity for DBT and 4,6-DMDBT HDS with the optimal reaction rate constant (12.2 mol·g−1·h−1, 6.7 mol·g−1·h−1) and turnover frequency (2.3 h−1, 1.4 h−1). By correlating to the catalyst acidity–activity and active phase–activity, the activity and selectivity were not only depended on the presence of Brønsted (B) acid and the total acid content but also associated with the dispersion and morphology of MoS2 slabs.

CoPMoV Sulfide Catalysts Supported on Natural Halloysite Nanotubes in Hydrotreating of Dibenzothiophene and Naphthalene

Mixed sulfided CoMo catalysts supported on γ-Al2O3 and halloysite nanotubes (HNTs) were synthesized by incipient wetness impregnation with salt solutions of Keggin-type phosphorus- and vanadium-containing heteropolyacids. The synthesized materials were characterized by low-temperature nitrogen adsorption, energy dispersive X-ray fluorescence analysis, temperature-programmed reduction (both for the oxide and sulfide catalysts), and Raman spectroscopy, and were tested in hydrogenation of naphthalene and hydrodesulfurization of dibenzothiophene. The HNT-supported catalyst exhibited a greater activity in these reactions.

The Influence of Metal–Support Interactions on the Performance of Ni-MoS2/Al2O3 Catalysts for Dibenzothiophene Hydrodesulfurization

In this present work, a new kind of sulfurized hydrodesulfurization catalyst was synthesized via the hydrothermal treatment of MoS2, NiCO3·2Ni(OH)2·4H2O, and Al2O3 precursors, followed by annealing under a H2 atmosphere, which does not require a sulfurization process compared to traditional preparation methods. The influence of the annealing temperature and the type of Al2O3 precursor on the interactions between MoS2 and Al2O3 were studied using X-ray fluorescence spectroscopy, X-ray diffraction, N2 adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicated an increase in the number of stacked layers of the MoS2 catalyst, accompanied by a decrease in the degree of decoration of Ni atoms onto MoS2 nanoslabs, as a result of the strengthened MoS2–Al2O3 interaction. Subsequently, the efficiency of hydrodesulfurization (HDS) was evaluated using dibenzothiophene as a representative reactant, while establishing a correlation between the structure of the catalyst and its performance. The catalysts, using pseudo-boehmite as the precursor and calcined at 500 °C, synthesized by calcining pseudo-boehmite as the precursor for Al2O3 at a temperature of 500 °C and possessing suitable metal–support interactions, exhibited a reduced number of MoS2 stacking layers and lateral dimensions, along with an optimal decoration degree of Ni atoms, thereby resulting in the highest level of HDS activity.

Study on the Performance of Ni-MoS2 Catalysts with Different MoS2 Structures for Dibenzothiophene Hydrodesulfurization.

Hydrodesulfurization (HDS) is an important process for the production of clean fuel oil, and the development of a new environmentally friendly, low-cost sulfided catalyst is key research in hydrogenation technology. Herein, commercial bulk MoS2 and NiCO3·2NiOH2·4H2O were first hydrothermally treated and then calcined in a H2 or N2 atmosphere to obtain Ni-MoS2 HDS catalysts with different structures. Mechanisms of hydrothermal treatment and calcination on Ni-MoS2 catalyst structures were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS). The catalytic performance of Ni-MoS2 catalysts was evaluated by the HDS reaction of dibenzothiophene (DBT) on a fixed bed reactor, and the structure-activity relationship between the structures of the Ni-MoS2 catalyst and the HDS of DBT was discussed. The results showed that the lateral size, the number of stacked layers, and the S/Mo atomic ratio of MoS2 in the catalyst decreased and then increased with the increase of the hydrothermal treatment temperature, reaching the minimum at the hydrothermal treatment temperature of 150 °C, i.e., the lateral size of MoS2 in the catalyst was 20-36 nm, the number of stacked layers of MoS2 was 5.4, and the S/Mo ratio in the catalyst was 1.80. In addition, the effects of different calcination temperatures and calcination atmospheres on the catalyst structures were investigated at the optimum hydrothermal treatment temperature. The Ni-Mo-S and NixSy ratios of the catalysts increased and then decreased with the increasing calcination temperature under a H2 atmosphere, reaching a maximum at a calcination temperature of 400 °C. Therefore, DBT exhibited the best HDS activity over the H-NiMo-150-400 catalyst, and the desulfurization rate of DBT reached 94.7% at a reaction temperature of 320 °C.

Modulation of Pt states on Pt/ZnO for atmospheric ultra-deep desulfurization of dibenzothiophene and sustainable utilization

The relationship between active metals and desulfurization activity, ultra-deep desulfurization at atmospheric pressure, and the sustainable utilization of ZnO-based adsorbents are positive significance for designing high-efficiency adsorbents in the field of reactive adsorption desulfurization (RADS) to achieve atmospheric zero sulfur and promote sustainable development of adsorbents. However, no efficient approach has been developed to systematically and simultaneously study all three aspects. In this work, we explored Pt/ZnO with different Pt states by metal-support interaction and oxygen vacancy modulation for atmospheric RADS of dibenzothiophene (DBT). The relationship between metal-active Pt states and the desulfurization activity of DBT was well established. The limiting step of atmospheric DBT desulfurization over Pt/ZnO was proposed, providing a new understanding and supplementing of the current RADS reaction. Moreover, the feasibility of Pt/ZnO to achieve ultra-deep desulfurization of DBT under atmospheric H2 pressure was analyzed from kinetics (51.8 kJ/mol) and thermodynamics (kRADS = 4.4*10^7). The spent Pt/ZnO adsorbent with a saturated sulfur capacity could be sustainable utilized as a highly efficient (408 μmolDBT/gPt*min) and sulfur-tolerant (155 h) catalyst for DBT hydrodesulfurization. The work aims to suggest designs for efficient and sustainable adsorbents based on Pt/ZnO for ultra-deep desulfurization at atmospheric pressure, establishing the scientific basis for industrial applications of this process.

Al-modified yolk-shell silica particle-supported NiMo catalysts for ultradeep hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene: Efficient accessibility of active sites and suitable acidity

Yolk-shell SiO2 particles (YP) with center-radial meso-channels were fabricated through a simple and effective method. Al-containing YP-supported NiMo catalysts with different Al amounts (NiMo/AYP-x, x = Si/Al molar proportion) were prepared and dibenzothiophene (DBT) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT) were employed as the probes to evaluate the hydrodesulfurization (HDS) catalytic performance. The as-prepared AYP-x carriers and corresponding catalysts were characterized by some advanced characterizations to obtain deeper correlations between physicochemical properties and the HDS performance. The average pore sizes of series AYP-x supports are above 6.0 nm, which favors the mass transfer of organic sulfides. The cavity between the yolk and the shell is beneficial for the enrichment of S-containing compounds and the accessibility between reactants and active metals. Aluminum embedded into the silica framework could facilitate the formation of Lewis (L) and Brønsted (B) acid sites and adjust the metal-support interaction (MSI). Among all the as-synthesized catalysts, NiMo/AYP-20 catalyst shows the highest HDS activities. The improved HDS activity of NiMo/AYP-20 catalyst is attributed to the perfect combination of excellent structural properties of the yolk-shell mesoporous silica, enhanced acidity, moderate MSI, and good accessibility/dispersion of active components.

Dendritic micro-mesoporous composites via nano-assembly strategy towards high-efficiency catalysts for hydrodesulfurization of dibenzothiophenes

Based on the three-dimensional center-radial framework structure of dendritic mesoporous silica nanospheres (DMSNs), a unique type of hierarchical micro-mesoporous composite material, namely, Beta-DMSNs (BD) was prepared through a nano-assembly method, which was utilized as superior supports for high-efficiency catalysts (NiMo/BD) for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The controllable introduction of Beta nanocrystals endows the NiMo/BD catalysts with more acidic and catalytic active sites, and shows no influence on the dendritic morphology of the mesoporous supports, resulting in the remarkable HDS performance of NiMo/BD catalysts. Owing to the dendritic open channels, high surface area, abundant acidic sites and highly dispersed MoS2 active phases, the optimized NiMo/BD exhibited superior HDS activities of 99.1% and 98.3% for DBT and 4,6-DMDBT, respectively, with the optimal reaction rate constant of 3.0 × 10−7 mol g−1 s−1 and 2.4 × 10−7 mol g−1 s−1, and with the turnover frequency of 5.9 × 10−4 s−1 and 4.8 × 10−4 s−1. Besides, the enhanced Brønsted acid and the synergistic effect of Brønsted & Lewis acid contributed to the superior isomerization selectivity for 4,6-DMDBT, which was conducive to its HDS.

Tuning active sites in MoS2-based catalysts via H2O2 etching to enhance hydrodesulfurization performance

A H2O2 etching strategy was adopted to introduce coordinatively unsaturated sites (CUS) on MoS2-based catalysts for dibenzothiophene (DBT) hydrodesulfurization (HDS). The CUS concentrations on MoS2 slabs were finely regulated by changing the concentrations of H2O2 solution. With the increasing H2O2 concentrations (0.1–0.3 mol/L), The CUS concentrations on MoS2 slabs increased gradually. However, the high-concentration H2O2 etching (0.5 mol/L) increased the MoOxSy and MoO3 contents on MoS2 slabs compared to etching with the H2O2 concentration of 0.3 mol/L, which led to the less CUS concentration in the sulfided Mo–H-0.5 catalyst than in the sulfided Mo–H-0.3 catalyst. A microstructure-activity correlation indicated that the CUS introduced by H2O2 etching on MoS2 slabs significantly enhanced DBT HDS. Different Co loadings were further introduced into Mo–H-0.3, which had the most CUS concentration, and the corresponding 0.2-CoMo catalyst with the highest CoMoS content (3.853 wt%) exhibited the highest reaction rate constant of 6.95 × 10−6 mol g−1 s−1 among these CoMo catalysts.

CoPMoV Sulfide Catalysts Supported on Natural Halloysite Nanotubes in Hydrotreating of Dibenzothiophene and Naphthalene

Mixed sulfided CoMo catalysts supported on γ-Al2O3 and halloysite nanotubes (HNTs) were synthesized by incipient wetness impregnation with salt solutions of Keggin-type phosphorus- and vanadium-containing heteropolyacids. The synthesized materials were characterized by low-temperature nitrogen adsorption, energy dispersive X-ray fluorescence analysis, temperature-programmed reduction (both for the oxide and sulfide catalysts), and Raman spectroscopy, and were tested in hydrogenation of naphthalene and hydrodesulfurization of dibenzothiophene. The HNT-supported catalyst exhibited a greater activity in these reactions.

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.