MoS2 Slabs Research Articles

Sulfidation of CoMoP catalysts: genesis of the Mo multiscale organization from oxides to sulfides

MoS2 active phase found in CoMoP/Al2O3 catalysts can be described as a multiscale Mo organization with MoS2 slabs and slab aggregates. The aim of this paper is to understand how such multiscale organization is formed from the oxide initial state. Sulfidation of two catalysts impregnated with 26 %wt MoO3, one dried, the other one freeze‐dried, has been followed ex situ by EXAFS, XPS and ASAXS. Initially, two types of Mo oxide precursors are present on the support such as dispersed MoO42‐ species and oxide aggregates constituted of heteropolyanions, polymolybdates and H6AlMo6O246‐ Anderson HPA (AlMo6). A 3‐step genesis is highlighted during the sulfidation regardless of the catalyst: i) AlMo6 depolymerizes into MoO42‐ entities from RT to 240°C, ii) MoO42‐ is preferentially sulfided compared to other entities and slab aggregates sulfidation is delayed in the presence of important MoO42‐ amount, iii) restructuration of the slabs within slab aggregates occurs during sulfidation of the latter and leads to their expansion. The drying method (drying or freeze‐drying) influences the kinetics of this 3‐steps genesis. As the freeze‐dried catalyst presents more AlMo6 and thus MoO42‐, a late restructuration within aggregates leads to larger ones. Initial speciation of the catalysts determines the final Mo multiscale organization.

A novel and facile strategy for the preparation of highly reactive NiMo/γ-Al2O3 hydrodesulfurization catalyst

Traditionally, the commercial Ni(Co)Mo(W)/Al2O3 hydrodesulfurization (HDS) catalysts were prepared with corresponding oxidation precursors and then sulfured with CS2 or H2S, which is complex and time-consuming. Herein, a novel “O-S exchanging” strategy was proposed to directly synthesize a series of highly efficient Ni-MoS2/Al2O3 HDS catalysts with various Mo loading using MoS42− solution as a novel active precursor, and their catalytic performances were evaluated for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS. The experimental results showed that under the same reaction conditions, the catalyst with 15 wt% MoO3 (S-CAT-15) exhibited a HDS rate up to 99.8 % for 240 h, which was not only nearly two times higher than that of O-CAT-15 counterpart prepared by the conventional oxidation precursor with the same metal loading, but also even 1.6 times higher than that of O-CAT-20 with a higher metal loading, demonstrating its excellent HDS performance and outstanding stability. The deep characterization analyses unveiled that the superior HDS performance of S-CAT-15 was attributed to this novel strategy, which not only notably improved the sulfidation of Mo species, but also considerably promoted the decoration of Ni atoms onto the edges of MoS2 slabs forming more reactive Type-II Ni-Mo-S sites, thereby remarkably enhancing the HDS performances of S-CAT catalysts. This work may offer a novel protocol to guide the fabrication of more efficient industrial hydrogenation catalysts in the future.

Engineering the accessibility of active sites in mixed 1 T-2H MoS2 nanoflowers via NaClO etching for deep hydrodesulfurization of dibenzothiophene

A NaClO etching strategy was adopted to engineer the active structure of mixed 1T-2H MoS2 nanoflowers and prepare efficient hydrodesulfurization (HDS) catalysts. In the original MoS2-P catalyst, the 2H-MoS2 phase was exposed after MoS2 slabs were etched using NaClO. Sodium ion insertion with high concentrations increased the interlayer spacing of MoS2 slabs and increased the transformation of 2H-MoS2 to 1T-MoS2 phases. With increase in the concentration of NaClO solution, the proportions of 1T-MoS2 in the MoS2-N-x catalysts initially increased and then decreased. They then reached a maximum when the NaClO concentration was 1.0 mol/L. Owing to the thermodynamic instability of 1T-MoS2, the proportions of 1T-MoS2 in the sulfided MoS2-P and MoS2-N-x catalysts were less than those of the corresponding unsulfided catalysts. However, among sulfided MoS2-P and MoS2-N-x catalysts, the sulfided MoS2-N-1.0 catalyst demonstrated the highest proportion of the 1T-MoS2 phase, the best dispersion of the MoS2 slabs, and the most coordinatively unsaturated sites, thus providing itself with the optimal HDS performance for removing dibenzothiophene.

Hydrophobic surface modification and morphology tuning of supported KNiMoS-based catalyst for synergistically enhanced higher alcohols synthesis via CO hydrogenation

MoS2-based catalysts have gained significant attention in higher alcohols synthesis (HAS) via CO hydrogenation. However, the water–gas shift (WGS) to produce CO2 in HAS is undesirable reaction, which will reduce the efficiency of carbon utilization. Here, we provide a facile strategy with hydrophobic surface modification and metal-support interaction modulation to design a series of KNiMoS/MgAl catalysts. The organic modified SiO2 shell with excellent hydrophobicity effectively shortens the residence of water formed in HAS, and further suppress the generation of CO2 and low-chain hydrocarbons. Moreover, the moderate metal-support interaction between MoS2-based active species and MgAl support can regulate the dispersion and sulfidation extent of MoS2 slabs to provide more active sites for alcohol formation. The MoS2 slabs with predominant double-layer structure enhance the C–C propagation and CO insertion in HAS. And as a result, the optimal KNiMoS/MgAl@Si(c)-5 achieves total alcohols selectivity of 74.7 %, C2+OH selectivity of 85.8 % in total alcohols, and C2+ alcohols space–time yield of 107.8 mg gcat-1h−1, where C2+ alcohols space–time yield is 3.50 and 2.71 times than those on KNiMoS/MgAl(H) and KNiMoS/MgAl, respectively. Notably, the total selectivity of CO2 and hydrocarbons is less than 23.2 %, and selectivity ratio of C2-4OH to methanol can be overturned from 1.9 to 6.0. The dependence of HAS performance on the morphology of MoS2 slabs were also demonstrated to get insight into the structure-performance relationship. This work provides a facile strategy with tunable hydrophobic surface and metal-support interaction of MoS2-based catalysts for further improvement of catalytic performance.

Flower-like hierarchical TS-1/Al2O3 composite supported NiMo catalysts for efficient hydrodesulfurization of dibenzothiophenes

Flower-like Al2O3 materials were successfully incorporated by TS-1 nanocrystals to synthesize Flower-like TS-1-Al2O3 (FTA) micro-mesoporous composite by a facile nano self-assembly method. FTA supported NiMo bimetallic catalysts (NiMo/FTA) were further constructed and applied to the hydrodesulfurization (HDS) reactions for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). FTA composites were constructed from flower-like pore structures stacked with nanosheets, which are conducive to the even load and dispersion of active species and the diffusion of macromolecular sulfur-containing compounds with relatively low resistance. The fabrication of TS-1 nanocrystals effectively enhanced the acidic sites, regulated the metal-support interaction, which could increase the stacking layer of MoS2 slabs, and producing more NiMoS-II type active phase. NiMo/FTA-10 presented the excellent HDS conversion of DBT (99.3 %) and 4,6-DMDBT (93.2 %) at 10 h−1, the highest reaction rate constant (2.6 × 10-7 mol g−1 s−1) and turnover frequency values (6.7 × 10-4 s−1) for 4,6-DMDBT HDS reaction. Compared to the direct desulfurization route (DDS), hydrogenation route (HYD) and isomerization route (ISO) can effectively eliminate the steric hindrance of 4,6-DMDBT, which is more conducive to the HDS reaction.

Optimizing the Incorporation Modes of TiO2 in TiO2-Al2O3 Composites for Enhancing Hydrodesulfurization Performance of Corresponding NiMoP-Supported Catalysts

TiO2-Al2O3 supports with different incorporation methods of titania were synthesized via three methods: impregnation (TA-I), co-precipitation (TA-CP), and co-precipitation–hydrothermal treatment (TA-HT). And the NiMoP catalysts prepared on the corresponding supports were evaluated for hydrodesulfurization (HDS) reactions. The results demonstrated that the Ti atoms in TA-I are attached to alumina through hydroxyl groups, while the Ti atoms in TA-CP and TA-HT can be dispersed in the alumina skeleton. Variations in the incorporation modes of TiO2 affect the support properties, consequently influencing the nature of the active metal on the supports. The Ti atoms dispersed in the Al2O3 skeleton allow an increase in the basic hydroxyl groups. Meanwhile, TiO2 in TA-CP and TA-HT can absorb hydrogen molecules and be partially reduced. Furthermore, metal species supported on the TA-CP and TA-HT are more easily reduced and better dispersed. For the NiMoP catalysts prepared with TA-CP and TA-HT, the Ti element promotes the sulfidation degree of Mo, besides shortening the average (Ni)MoS2 slab. The catalysts prepared with TA-CP exhibited superior activity for 4,6-DMDBT hydrodesulfurization. This can be ascribed not only to the relatively high sulfidation degree of Mo and proportion of the NiMoS active phase but also to the well-dispersed (Ni)MoS2 slabs. Moreover, the Ti4+ ions dispersed in the Al2O3 skeleton can be partially reduced to act as electron donors, enhancing the metallic character of the S layers in MoS2, which facilitates the improvement of the hydrogenation desulfurization activity.

Controlled construction of Co3S4@CoMoS yolk-shell sphere for efficient hydrodesulfurization promoted by hydrogen spillover effect

A yolk-shell structured Co3S4@CoMoS catalyst was prepared through Oswald ripening method and subsequently used for hydrodesulfurization (HDS) reaction. The shells, constructed from Co-promoted MoS2 nanosheets, possess abundant active sites and facilitate the adsorption of reactants through the development of pore channels. The MoS2 sheets are arranged in a staggered and convoluted manner, creating numerous defect sites. The shorter MoS2 slabs provide a wide distribution of reactive sites, ensuring efficient reactions. The Co3S4 species within the inner core acts as an auxiliary active phase, inducing the hydrogen spillover effect in the HDS system. This facilitates the transfer of active hydrogen species to the CoMoS shell, where both CoMoS and Co3S4 phases synergistically enhance the HDS reaction. The Co3S4@CoMoS catalyst achieved up to 99.2% dibenzothiophene (DBT) conversion and 94.9% 4,6-dimethyldibenzothiophene conversion at the lower dosage (30 mg). The structure-activity relationships between active phase and HDS activity were investigated via in-situ infrared spectroscopy and other characterizations as well as density functional theory calculations.

Ordered mesoporous Mg-modified silica to confine MoS2 slabs with high sulfidation and dispersion for higher alcohol synthesis via CO hydrogenation

KNiMoS as one of the most promising catalysts for the synthesis of higher alcohols (HA) from syngas but still remains challenge in the trade-off between catalytic activity and selectivity. Herein, a series of Mg-modified mesoporous silica (Mg-MS-x) with tunable morphology and pore size were synthesized by the modified-Stöber method which serve as support for KNiMoS catalysts to confine MoS2 active phases for higher alcohol synthesis (HAS) via CO hydrogenation. The ordered mesoporous Mg-modified silica enable the adjustable structure of MoS2 slabs via confinement effect, and thus enhancing the dispersion and proportion of NiMoS active phases. As a result, KNiMoS/Mg-MS-20 with dominant double-layer MoS2 stacking (∼31.2 %) and proper slab length presents the highest alcohol selectivity of 66.3 %, C2+OH selectivity of 80.5 % in the alcohol and space–time yield (STY) of 91.6 mg g-1h−1 for C2+OH. The connections between HAS performance and the structural property of ordered mesopore confined MoS2 catalysts were also discussed to get insight into the structure-performance relationship. This work proposed a promising route to fabricate ordered mesoporous silica confined KNiMoS with different morphology and pore size, which significantly enhance the selectivity of HA and the ratio of C2+OH/ROH in selective CO hydrogenation.

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.

In situ synthesis of mesoporous NiS2-MoS2 sphere-flower hybrid for hydrodesulfurization of thiophene and 4,6-dimethyl-dibenzothiophene

A series of new NiS2-MoS2-x (x = 0–0.5) sphere-flower hybrids with different Ni/Mo molar ratios, synthesized via a one-pot hydrothermal method, were used as catalysts for hydrodesulfurization (HDS) of thiophene (TP) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT). The characterizations show that the microstructure of MoS2, including the size of MoS2 nano-flowers, the length of MoS2 slabs, and the number of defects, was regulated by changing Ni/Mo ratios. Increasing the Ni/Mo ratio in the NiS2-MoS2-x catalysts significantly boosts their HDS activity, with the optimum ratio being 0.2. In addition, the NiS2-MoS2-0.2 catalyst exhibits the best direct desulfurization performance, which is associated with the minimum ratio of average slab length (Lav) to average stacking number (Nav) as well as the highest concentration of Ni-promoted Mo sites and sulfur vacancies. Moreover, Ni-containing NiS2-MoS2-x catalysts, characterized by a highly stable sphere-flower configuration, exhibit superior structural stability and catalytic durability than the Ni-free NiS2-MoS2-0 catalyst.

NiMoS nanocubes for the selective removal of sulfur from 3-methyl-thiophene

In this study, NiMoS nanocubes were prepared by simple hydrothermal synthesis using low-cost precursors. The HRTEM micrographs exhibited variation in the size and definition of the particle shape with the Mo/Ni molar ratio. The crystallographic composition of the nanocubes also varies with the molar ratio passing from Ni3S4 polydymite, NiSO4·6 H2O, and NiS phases in the Mo/Ni low values to NiS2 in the Mo/Ni= 1.0 as revealed by the X-ray diffraction study. Meanwhile, the surface of the nanocubes resulted enriched with Mo as the Mo/Ni ratio increases, as XPS analysis demonstrated. These materials exhibited outstanding catalytic activity in the hydrodesulfurization reaction of a naphtha model compound under atmospheric pressure conditions. The selectivity displayed indicated low saturation of the C5 olefins obtained as products in all ranges of temperature tested. The high activity observed was explained in terms of the Ni inverse promotion effect on MoS2 slabs present at the nanocubes outer surface.

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.

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.

Active phase morphology engineering of NiMo/Al2O3 through La introduction for boosting hydrodesulfurization of 4,6-DMDBT

Herein, we designed and constructed a mesoporous LaAlOx via a solvent evaporation induced self-assembly protocol. The structure and physicochemical property of the corresponding NiMo supported catalyst was analyzed by a set of characterizations, and its catalytic activity was investigated for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene. It has confirmed that the incorporation of La profoundly facilitate the generation of “Type II” NiMoS phase by weakening the interaction of Mo–O–Al leakage and promoting the sulfidation of both Ni and Mo oxides as well as changing the morphology of Ni promoted MoS2 slabs, thereafter boosting the HDS performance substantially. The finding here may contribute to the fundamental understanding of structure-activity in ultra-deep desulfurization and inspire the advancement of highly-efficient HDS catalyst in future.

Understanding the Role of Potassium Addition on the Active Centers and Reaction Pathway of MoS2 Catalysts for Water Gas Shift Reaction

AbstractMoS2 is a promising sulfur‐resistant candidate for water‐gas shift (WGS) reaction, and its catalytic efficiency can be promoted by alkali metal. In this work, a series of K‐modified MoS2/Al2O3 catalysts with variable K/Mo ratios were prepared to elucidate the promotion role of potassium through IR spectroscopy studies. CO adsorption followed by IR spectroscopy shows that after potassium addition the number of accessible edge sites of MoS2 slabs is decreased. Meanwhile, the downward shift of v(CO/MoS2) indicates that the presence of potassium increases the electronic density of Mo atoms. This electronic effect activates terminal S atoms, favoring their reaction with CO to form COS at lower temperature than in absence of K. Additionally, conversely to the case of MoS2/Al2O3 catalysts, little or even no formate species are observed on K‐modified MoS2 catalysts during IR operando studies, implying a change of the WGS reaction route that would explain the beneficial effect of K on MoS2 edge site activity.

Synthesis of cube MgO@AC and catalytic performance of its supported CoMo for hydrodesulfurization of 4,6-dimethyldibenzothiophene

The cube MgO has been modified with different weight percent of activated carbon, which was synthesized by the carbon precursor pyrolysis and pre-deposition method. The fluidity of asphalt powder at high temperatures was used to coat MgCO3 and asphalt powder was activated with CO2 released in the high-temperature calcination process of MgCO3 precursor MgO, which complement each other. CoMo supported catalyst was successfully synthesized and used for HDS of 4,6-DMDBT. The introduction of the non-homogeneous carbon layers can increase the number of stacking layers of the MoS2 slab as well as shorten the length, indicating that carbon layers can effectively adjust the surface properties of MgO, which are in favor of the formation of “type Ⅱ” CoMoS active phase. The highest HDS conversion rate of 84.71 % was observed over the CoMo/M@AC-0.2 catalyst at 300 ℃ and 8 h−1 conditions, which was 32.78 % higher than that of the CoMo/Al2O3 catalyst.

Influence of the Ageing and Drying Steps of a CoMoP/γ‐Al2O3 Catalyst onto the Multi‐Scale Molybdenum Active Phase Organization

AbstractTo study the influence of ageing and drying steps onto the multiscale Mo active phase arrangement (i. e. MoS2 slabs and slab aggregates), a series of highly loaded CoMoP/γ‐Al2O3 catalysts aged, unaged, dried or freeze‐dried were prepared and tested in toluene hydrogenation. Electron Probe Micro Analyses (EPMA) and Anomalous Small Angle X‐Ray Scattering (ASAXS) permit to highlight the influence of each preparation steps. A growth of Mo entities occurs during ageing along with metal diffusion inside the support and leads to longer slabs. The same occurs during drying with metal redistribution due to solvent evaporation. Concomitantly, a fragmentation of slab aggregates takes place and leads to numerous small slabs aggregates. Slab length and aggregates amount were found to drive the catalytic activity, which translates the relationship between activity, number of active sites and their accessibility. Conversely, macroscopic metal distribution into the extrudates appears to have no impact on the catalytic performance.

Impacts of support properties on the vacuum residue slurry-phase hydrocracking performance of Mo catalysts

To deeply understand the effects of support properties on the performance of Mo-based slurry-phase hydrocracking catalysts, four Mo-based catalysts supported on amorphous silica alumina (ASA), γ-Al2O3, ultra-stable Y (USY) zeolite and SiO2 were prepared by the incipient wetness impregnation method, respectively, and their catalytic performances were compared in the vacuum residue (VR) hydrocracking process. It is found that the Mo/ASA catalyst exhibits the highest VR conversion among the different catalysts, indicating that both the appropriate amount of acid sites, especially B acid sites and larger mesoporous volume of ASA can enhance the VR hydrocracking into light distillates. Furthermore, Mo catalysts supported on the different supports show quite different product distributions in VR hydrocracking. The Mo/ASA catalyst provides higher yields of naphtha and middle distillates and lower yields of gas and coke compared with other catalysts, it is attributed to the highest MoS2 slab dispersion, the highest sulfuration degree of Mo species, and the most Mo atoms located at the edge sites for the Mo/ASA catalyst, as observed by HRTEM and XPS analyses. These features of Mo/ASA are beneficial for the hydrogenation of intermediate products and polycyclic aromatic hydrocarbons to restrict the gas and coke formation.

A study on the role of Ti/Si atomic ratios in the hydrodenitrogenation activity of NiMo/TiO2-SiO2 catalyst

TiO2-SiO2 composites with different Ti/Si atomic ratios were synthesized by an optimized pre-hydrolysis-co-precipitation method while the corresponding NiMo supported hydrodenitrogenation (HDN) catalysts were prepared by incipient wetness impregnation method. The significant structure of serial TiO2-SiO2 composites was determined by XRD, FT-IR, N2 physical adsorption–desorption and NH3-TPD techniques, and the distributions of TiO2 particles within SiO2 matrix were also illustrated under the help of SEM-EDS. In this work, it can be concluded that the Ti/Si atomic ratio has a large effect on the textural characteristics and the acidity distribution of composites. Among the self-made composites, TS-1 samples (Ti: Si = 1) presented the highest specific surface area (SBET = 230.42 m2/g) and the highest proportion of weak acidity. And then, characterization of the NiMo/TS-n catalysts were performed by H2-TPR, HRTEM and XPS. Among the NiMo/TS-n catalysts, NiMo/TS-1 catalysts presented the particularly favorable dispersion of active metals and the largest proportion of “Ni-Mo-S” active phase. The results of the adsorption tests showed that NiMo/TS-4 catalysts presented the maximum value of adsorption coefficient (ACQ). Compared these ACQ, these adsorption sites of quinoline were attributed to the CUS supported by “Ni-Mo-S” structures as well as the strong acid sites by excessive TiO2 particles. Finally, these catalysts were tested by feeding 1.0 wt% quinoline as the reactant under the constant reaction conditions. However, the results of HDN evaluation showed that NiMo/TS-1 catalyst exhibited the best HDN activity (51.31 %) and the highest value of turnover frequency (TOFQ = 4.77 h−1), which was attributed to the formation of maximum Ti-O-Si bonds providing moderate acidity, appropriate MSI, suitable size of MoS2 slabs and “Ni-Mo-S” active phase having high concentration of CUS and Mo-SH/S2− species.

Resta-like preconditioning for self-consistent field iterations in the linearized augmented planewave method

Convergence in self-consistent-field cycles can be a major computational bottleneck of density-functional theory calculations. We propose a Resta-like preconditioning method for full-potential all-electron calculations in the linearized augmented planewave method to smoothly converge to self-consistency. We implemented this preconditioner in the exciting code and apply it to the two semiconducting systems of MoS2 slabs and P-rich GaP(100) surfaces as well as the metallic system Au(111), containing a sufficiently large amount of vacuum. Two magnetic systems of 19-atoms Fe and Co are also considered. Our calculations demonstrate that the implemented scheme performs reliably as well as more efficiently regardless of system size, suppressing long-range charge sloshing. While the suitability of this preconditioning higher for semiconducting systems, the convergence for metals is, depending on the system, only slightly de- or increased and thus still trustworthy to apply. Furthermore, a mixing algorithm with the preconditioner shows an improvement over that with the Kerker preconditioner for the investigated semiconducting systems.