CoMo Sulfide Research Articles

Influence of the crystalline structure of Co-Mo precursors on the hydrodesulfurization performance of unsupported tube-like Co-Mo sulfide catalysts

Influence of the crystalline structure of Co-Mo precursors on the hydrodesulfurization performance of unsupported tube-like Co-Mo sulfide catalysts

CoMo Sulfide Catalysts Supported on Natural Halloysite Nanotubes: Dealumination as an Effective Approach to Improve Catalytic Performance

CoMo Sulfide Catalysts Supported on Natural Halloysite Nanotubes: Dealumination as an Effective Approach to Improve Catalytic Performance

Synergistic conversion of acid gases (H2S and CO2) to valuable chemicals: Carbonyl sulfide synthesis over vacancy-defective CoMo sulfide catalysts

Synergistically convert acid gases to valuable chemicals is meaningful. Herein, unsupported CoMo sulfide catalysts with abundant sulfur vacancies were fabricated to attain synergistical conversion of H2S and CO2 to COS. Various metal sulfides were obtained, such as Co3S4, Co9S8 and vacancy-defective MoS2. Besides, simultaneous sulfidation of Mo with Co prompted formation of CoMoS phase, which enhanced catalytic performance. Among them, CoAlMo-S catalyst exhibited superior activity, allowing for equilibrium COS yield (6%, 300 ℃). DFT calculations indicate that chemisorbed H2S induced CO2 activation via van der Waals interaction between C atom in CO2 and S atom in H2S, contributed to efficient C–S bond formation. Sulfur vacancy significantly promoted dissociative adsorption of H2S while Co atom in CoMoS phase was beneficial for CO2 adsorption and facilitated C–S bond construction. This work not only achieves H2S pollution control and carbon emission reduction, but also provides an alternative approach to synthesis COS.

Effects of temperature and time on the facile low-temperature pre-sulfurization of tube-like unsupported Co-Mo catalysts for hydrodesulfurization

A Co-Mo sulfide catalyst with tube-like structure was prepared through a low-temperature pre-sulfurization process using rod-like CoMoO4 as the precursor. The pre-sulfurization temperature greatly affected the total pore volume, the concentration of CoMoS species, the microstructure of (Co)MoS2 slabs and the catalytic desulfurization activity. The increased temperature can promote the formation of hollow structure and the sulfurization degree of the precursor. It was found that the excessive temperature induced the Co atoms to form more isolated Co9S8 species, hindering the formation of highly active CoMoS species. Therefore, appropriate temperature is more favorable to form the (Co)MoS2 slabs with shorter length and higher stacking number, leading to more coordinatively unsaturated sites, especially the corner sites. According to the results of hydrodesulfurization reaction, the reaction rate of dibenzothiophene and the yields of liquid products are highly depended on the number of surface-active sites, which are mainly originated from the Type II CoMoS species. Moreover, the extended pre-sulfurization time can further improve the catalytic desulfurization activity of the catalyst at an appropriate pre-sulfurization temperature.

Catalytic depolymerization of the dealkaline lignin over Co–Mo–S catalysts in supercritical ethanol

In this work, lignin depolymerization was examined over CoMo sulfide catalysts supported on different carriers in supercritical ethanol system. The temperature, time, MoS2 and carrier effects on the lignin depolymerization were investigated. 95.76% liquefaction yield with negligible char was achieved over Co–Mo–S/ZrO2 at 340 °C for 150 min. The liquid product was mainly composed of C4–C8 alcohols, C4–C10 esters and C7–C10 aromatic compounds. The synergistic effect of active sites and acid-base sites on support played an important role in lignin depolymerization. Furthermore, the Co–Mo–S/ZrO2 catalyst is reusable with 8% loss in liquefaction yield after 5 cyclic runs. We believe that acid/base carriers or additives that can promote the medium to generate abundant free radicals or ions to replace external hydrogen pressure are one of the prospects for the design of depolymerization lignin catalysts.

Tailoring of Surface Acidic Sites in Co-MoS2 Catalysts for Hydrodeoxygenation Reaction.

CoMo sulfides are typical catalysts for selective hydrodeoxygenation (HDO) of phenolics to aromatics which is important in bio-oil upgrading. However, it is still a challenge to promote the intrinsic activity of Co-MoS2 catalysts. Defect chemistry provides a good option to improve surface reactivity in catalysis. In this work, we report a facile H2O2 etching method to tailor the concentration of surface acidic sites. The molar ratio of H2O2/MoS2 can be altered to tune sulfur defects on the MoS2 surface for stabilizing Co species to form CoMoS active sites. The optimized Co-MoS2-2 catalyst, with the highest concentration of acidic sites, exhibits 3.4 times higher activity than the Co-MoS2-0 sample in the HDO of p-cresol to toluene. It is also found the HDO activity shows a linear relationship with the amount of surface acid (both Lewis and Brønsted acid) over the Co-MoS2-x catalysts. We believe that the understanding of the role of surface acidity would provide new opportunities for the rational design of efficient Co-MoS2 catalysts.

Co-promoted few-layer and defect-rich MoS2 for enhanced hydrodeoxygenation of p-cresol

Unsupported CoMo sulfide catalysts are good candidates in the hydrodeoxygenation (HDO) of phenol compounds to aromatics which is important for bio-oil upgrading. However, the key to prepare efficient catalysts is how to increase the content of Co-Mo-S active phase as much as possible. Herein, a dual strategy of layer and defect engineering was realized for the synthesis of few-layer and defect-rich MoS2 (MoS2-FL-DR) through a simple one-pot hydrothermal method. By decreasing the layer number and manufacturing abundant defects on the basal planes, more coordinatively unsaturated sites (CUS) were formed to provide additional sites to accommodate Co atoms. After promoted with Co, Co/MoS2-FL-DR exhibited an excellent performance in the HDO of p-cresol, with p-cresol conversion of 100 % and toluene selectivity of 99.7 % at 230 °C. This catalyst also showed a relative good stability after reaction for 72 h. The excellent performance was attributed to the few-layer and defect-rich structure of MoS2 and the formation of large amount Co-Mo-S active phase.

Combined HR TEM and STEM-EDX evaluation – The key to better understanding of the Co-Mo sulfide active phase in real-life Co-Mo-P/Al2O3 catalysts

Co-Mo/Al2O3 used model and real-life catalysts from a diesel test are characterized by HR (S)TEM-EDX on ultra-thin sections to give a very complete description of MoS2 morphology, sulfidability and CoSx segregation. Image analysis is used to calculate the populations of different Mo sites. The low metal model catalyst contains only small 1–3 nm MoS2 structures. The real-life catalysts with higher metal content (dried Type II versus calcined Type I/II, H2S gas phase versus liquid phase sulfiding) are more complex and heterogeneous. Their MoS2 dispersion and Co segregation are related to the local compositions and start-up procedure. The median stack length and stacking from image analysis are much lower than the first visual impressions, dominated by short and large structures, respectively. The real-life catalysts are different from the model catalyst with respect to active phase characteristics and balance between brim and edge sites, which results in different catalyst activities and selectivities.

Significant impact of γ-Al2O3 facet structure on the character and performance of surface Co-Mo sulfides for CO removal in H2 fuel via water gas shift

Three morphologically uniform γ-Al2O3 crystallites [Al2O3 hexagonal plates (Al2O3-HP), stacked hexagonal plates (Al2O3-SHP) and rods (Al2O3-R)] were controllably synthesized. The Co-Mo oxide precursor was loaded on these γ-Al2O3 substrates via aqueous incipient wetness impregnation and transformed to the sulfides under 10% H2S/H2 (v/v) atmosphere. The mainly exposed facet of Al2O3-HP and Al2O3-SHP was identified to be the (110) and (100)/(111), respectively; whereas a polycrystalline structure was observed over Al2O3-R. The original structural feature of oxide precursors, i.e., 2D polymeric/monomeric as well as 3D polymeric/MoO3 species substantially varied over Al2O3-HP, Al2O3-SHP, and Al2O3-R, which in turn determines the effectiveness in sulfidation of surface oxide precursors. The richness of MoS2/Co9S8/Co-Mo-S species, and less fraction of partially sulphurated CoMoOxS2 as well as CoOx/SOx2− entities were recognized over Al2O3-HP. Based on the areal activity at 250 °C, the sulfides-Al2O3 (110) interface is approximately 6–13.8 times more active than the poly-crystalline or commercial γ-Al2O3 supported sulfides for water gas shift (WGS) in a hydrogen-rich stream. The sulfides-Al2O3 (110) interface also notably outperformed the sulfides-Al2O3 (100)/(111) interfaces for the reaction.

Synthesis of unsupported Co-Mo hydrodesulfurization catalysts with ethanol-water mixed solvent: Effects of the ethanol/water ratio on active phase composition, morphology and activity

Co-Mo sulfide catalysts with different particle size and structures were prepared in ethanol-water mixed solvent followed by a low-temperature sulfurization process, and were tested in dibenzothiophene hydrodesulfurization. The effects of the ethanol/water ratio on the particle size of precursors, active phase composition, active site number, morphology, and hydrodesulfurization activity of the final catalysts were investigated. The atomic ratio of Co/Mo and active phase morphology of catalysts closely relate to the dielectric constant of ethanol-water mixed solvent. Appropriate dielectric constant favors the formation of (Co)MoS2 slabs with shorter length (∼ 5.0 nm) and higher stacking number (∼ 4.3 layers), resulting in more coordinatively unsaturated sites, especially in the corner sites. The catalytic activity not only depends on the active sites of CoMoS phase, but also on that of Co9S8 and MoS2 phases because of synergistic effect. For MoS2 and CoMoS phases, the corner sites show higher direct desulfurization activity than the edge sites.

Multiscale structural optimization: Highly efficient hollow iron-doped metal sulfide heterostructures as bifunctional electrocatalysts for water splitting

Hollow iron-doped Co–Mo sulfide (H–Fe–CoMoS) heterostructures with a highly efficient water-splitting catalytic ability were achieved by applying a multiscale optimization strategy. Morphological and compositional optimization on a macroscale achieved by assembling a bimetallic Co–Mo sulfide (CoMoS) heterostructure in a hollow-structured composite (H–CoMoS) gave the electrocatalyst an ability to conduct enhanced bifunctional activities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Intrinsic electronic structure optimization on a microscale achieved by introducing a small amount of iron (Fe) into H–CoMoS (H–Fe–CoMoS) further improved its catalytic activity and stability. Electrochemical measurements revealed that this multiscale structural optimization promoted enhanced electrical conductivity and increased the number of electrochemical active sites on the H–Fe–CoMoS, leading to its remarkable electrocatalytic performance as a bifunctional catalyst for both HER and OER in alkaline media. The H–Fe–CoMoS showed overpotentials of 282 mV and 137 mV to achieve a current density of 10 mA cm −2 for OER and HER, respectively, which are comparable to the performance of the benchmark OER catalyst RuO 2 and HER catalyst Pt/C. • A multiscale optimization strategy is used to get a highly efficient electrocatalyst. • Bimetallic CoMoS heterostructures show bifunctional activities for both HER and OER. • Nanosized hollow metal sulfide was prepared using block polymer as a soft-template. • Fe-doping into the catalyst facilitates water splitting kinetics.

Highly dispersed Co-Mo sulfide nanoparticles on reduced graphene oxide for lithium and sodium ion storage

A novel hybrid, highly dispersed spinel Co-Mo sulfide nanoparticles on reduced graphene oxide (Co3S4/CoMo2S4@rGO), is reported as anode for lithium and sodium ion storage. The hybrid is synthesized by one-step hydrothermal method but exhibits excellent lithium and sodium storage performances. The as-synthesized Co3S4/CoMo2S4@rGO presents reversible capacity of 595.4 mA·h·g−1 and 408.8 mA·h·g−1 after 100 cycles at a current density of 0.2 A·g−1 for lithium and sodium ion storages, respectively. Such superior performances are attributed to the unique composition and structure of Co3S4/CoMo2S4@rGO. The rGO provides a good electronically conductive network and ensures the formation of spinel Co3S4/CoMo2S4 nanoparticles, the Co3S4/CoMo2S4 nanoparticles provide large reaction surface for lithium and sodium intercalation/deintercalation, and the spinel structure allows fast lithium and sodium ion diffusion in three dimensions.

Sulfated ZrO2 supported CoMo sulfide catalyst by surface exsolution for enhanced hydrodeoxygenation of lignin-derived ethers to aromatics

Catalytic transformation of lignin is a sustainable way to provide aromatics, which depends on the structure and property of catalytic sites. A bifunctional sulfated ZrO2 supported CoMo sulfide catalyst has been synthesized by in situ exsolution approach. The exsolved CoMo-sZr(exs) catalyst significantly enhanced the initial C–O bond cleavage rate (0.058 mol·g−1·h−1) compared to the impregnated and physically mixed sulfated ZrO2 supported CoMo sulfide catalysts. Notably, the reusability tests also showed that the as-prepared catalyst presented total ethers conversion of 94% with aromatics yield of 86% after four consecutive cycles. This was related to the appropriate sulfide-support interaction, acid sites and highly-dispersed CoMo sulfide, in conformity with the catalyst characterization. Thereby it could facilitate reactant adsorption and effectively break down the C–O bonds in lignin derived fragments to form aromatics. This work points out a new avenue for the design of effective bifunctional catalysts for lignin depolymerization.

Hydrodeoxygenation of oleic acid and palmitic acid to hydrocarbon-like biofuel over unsupported Ni-Mo and Co-Mo sulfide catalysts

Second generation biodiesel, so-called bio-hydrogenated diesel (BHD), can be produced from hydrotreatment of vegetable oils. The hydrogenation (HDO) of oleic acid and palmitic acid as model compounds of palm oil over unsupported Ni-Mo and Co-Mo sulfide catalysts was performed in a Parr reactor to produce BHD. The effects of reaction parameters: temperature, hydrogen pressure and the atomic ratio of catalysts (Ni/(Ni + Mo) or Co/(Co + Mo)) on the conversion and product yields (mainly n-C15, n-C16, n-C17 and n-C18 hydrocarbons) were evaluated. The results show that the high pressure favored HDO pathway, while high temperature strongly affected the decarboxylation and decarbonylation pathways. At optimal conditions for oleic acid HDO, the efficient catalyst was NiMoS2 catalyst (Ni/(Ni + Mo) = 0.2) which gave high oleic acid conversion (100%), n-C18 selectivity (78.8%) and n-C18 yield (70.3%) whereas, for palmitic acid HDO, NiMoS2 catalyst (Ni/(Ni + Mo) = 0.2) also gave high palmitic acid conversion (95.2%), n-C16 selectivity (78.5%) and n-C16 yield (65.6%).

Leaching and Preparation of Co-Mo Sulfide/Oxide Nanoparticles from Spent Catalyst

Acid leaching of spent molybdenum (Mo) catalyst followed by a simple pH-selective precipitation route for recovery of Co-Mo sulfide/oxide complexes in high yield has been investigated. The effect of leaching parameters such as temperature, pulp density, particle size, time, and acid concentration on the dissolution efficiency of aforesaid metal ion was studied, revealing that the Mo and Co dissolution increased with increase in the acid concentration, temperature, and contact time but increase in the particle size led to the opposite effect on the metal ion dissolution. The optimized leaching parameters, which resulted in dissolution of 95% Mo along with 53% Co under the size fraction of 90 + 75 µm, were 20% pulp density, 3% H2SO4 concentration (V/V), 80°C, and contact time of 3 h. Precipitation experiments were carried out on mixed Co-Mo sulfide/oxide nanoparticles at different pH values, adjusted using Na2S or NaOH. The Co-Mo sulfide nanoflakes obtained at the optimum pH were annealed and their physicochemical properties characterized. The feasibility of precipitation of mixed Co-Mo oxide material by pH adjustment was also shown. At low pH, chemically bound Co-Mo oxide with crystalline nature was observed, whereas at high pH, physically entrapped Mo phase on Co(OH)2 was detected. Scanning electron microscopy (SEM) of the precipitate obtained at pH 5 revealed nanofiber crystalline grains, whereas the precipitate obtained at pH 7 showed gel-like nature with aggregate morphology, and at pH 12, the precipitate was formed of denser amorphous aggregates with larger particles. A flow sheet based on the optimal results for preparation of Co-Mo sulfides or oxides is presented and discussed.

Characterisation and performance of hydrotalcite-derived CoMo sulphide catalysts for selective HDS in the presence of olefin

Infrared spectroscopy of adsorbed CO showed that, in hydrotalcite-derived CoMoMgAl catalysts, Co-promoted sites catalyse HDS, and un-promoted sites, hydrogenation.

Regeneration of CoMo Sulfide Exhaustive Hydrofining Catalysts Using Organic Reagents

Commercial cobalt-molybdenum catalyst after use for two years for diesel fraction hydrofining was oxidatively regenerated and activated with organic acids (citric and thioglycolic), ethylene glycol, and combined solution. It is shown that the main reasons for the loss of activity of the studied catalyst during its use are coke deposition on the catalyst surface and change in the properties of the applied active phase, which intensify in the oxidative regeneration process. Treatment of the oxidatively regenerated catalyst with solution of the studied reagents can fully restore the activity in the reaction of hydrodesulfurization of dibenzothiophene, and in the case where combined citric acid and ethylene glycol solution is used the observed hydrodesulfurization reaction rate constant exceeds the value obtained on fresh catalyst.

Binary and Ternary Earth-Abundant Transition Metal Phosphides As Electrocatalysts and Photocatalysts for Water Splitting

To provide a sustainable carbon free energy system while moving away from fossil fuels and greenhouse gas (CO2) generating energy sources, an inexpensive and reliable process to produce hydrogen has to be implemented. Water splitting by electrolysis has been thought of as the ideal way to produce hydrogen but the current electrolysis of water requires energy or rare materials that make the process neither carbon independent or feasible due to the amount energy gained vs energy input. In this talk there are two methods to perform the electrolysis of water: a) electrocatalytic water-splitting and b) solar photo-electrochemical water-splitting. Recently, transition metal phosphides (TMP) have shown promising catalytic properties for the water splitting half reactions. Two key aspects to studying TMPs for the electrolysis of water are 1) to generate hydrogen with as little energy input as possible; meaning using materials that can harness solar energy or that have significantly low overpotentials for each water splitting half reactions and 2) to find competitive materials to rival the performance and stability of platinum and other noble metals so that industrial production and manufacturing may be achieved. This talk will focus on binary and ternary transition metal phosphides as electocatalysts and photocatalysts for the hydrogen and oxygen evolution reactions; transition metals of focus primarily include Nickel, Molybdenum, and Cobalt with Platinum and Titanium as reference metals. Phosphorus (P) atoms have been determined to stabilize the TMP surface structure and thus the concentration of surface P is a key factor in controlling the surface activity. To control size, shape and crystallinity, a colloidal synthesis method was used to synthesize the nano particles. MoxCo2-xP and Ni2-xMoxP ternary TMPs were synthesized owing to their synergistic effects towards electrocatalysis. These two specific ternary phosphides are being considered for the proposed work influenced by commercial hydrotreating ternary catalyst system (sulfided Co-Mo and Ni-Mo). Nickel phosphide is of primary interest resulting from its consistent performance over other TMPs as an electrocatalyst for water splitting. As electrocatalysts, TMPs show low overpotentials and good stability for the hydrogen-evolution reaction (HER) and oxygen-evolution reaction (OER) under relevant current densities (10 mA/cm2) without any sacrificial agent present. The particles show high stability under most conditions, specifically in acidic electrolytes. In our group, work has been done to synthesize, characterize and test TMP nanoparticles as electrocatalysts and photocatalysts using PEC methods for the HER and OER to understand the material’s electrochemical behavior. Electrode preparation methods may influence the behavior, stability and reproducibility of the electrode. Therefore, multiple preparation methods were conducted to determine the true performance of the material. FTO on glass and Titanium foil were used as substrates/current collectors for the catalytic nano-particles. The electrocatalytic performance of the binary and ternary TMPs have been evaluated as well as the photocatalytic performance. The photocatalytic testing was evaluated under 1 SUN (100mW/cm2) illumination from a 150 W Xe Lamp with and without an AM1.5 filter. The photocatalytic performance was evaluated for the materials tuned to have more semiconductor characteristics and that show signs of photovoltage. Various ratios of metal to phosphide and metal to metal alloys were examined to study the effect of the electrocatalytic and photocatalytic performance and the material’s stability.

Highly selective hydrodesulfurization of gasoline on unsupported Co-Mo sulfide catalysts: Effect of MoS2 morphology

To remove sulfur-containing molecules from gasoline via hydrodesulfurization (HDS) while minimizing olefin hydrogenation is quite difficult. In this work, we report that an unsupported Co-Mo catalyst can achieve high HDS activity with low activity in olefin hydrogenation. The HDS selectivity of the Co-Mo catalyst is fourfold that of CoMo/γ-Al2O3 for both model gasoline and full-range FCC gasoline. For Co-Mo sulfide catalysts, we found that the MoS2 slab morphologies such as curvature, stacking number and slab length were important factors influencing the catalytic performance. Co-Mo catalyst with longer slab length and higher stacking number of MoS2 exhibited higher HDS selectivity. Nevertheless, it was found that the slab length showed much more influence on HDS selectivity than the stacking number. Furthermore, the curved MoS2 could facilitate the olefin isomerization. Present work provides a new way to develop a highly selective HDS catalyst by controlling the MoS2 morphology.

STUDY OF CoMo CATALYSTS SUPPORTED ON HIERARCHICAL MESOPOROUS ZEOLITES FOR HYDRODESULFURIZATION OF DIBENZOTHIOPHENE

Three zeolites systems (ZSM-5, Faujasite Y, Mordenite) were prepared by using a supramolecular surfactant assembly method. Samples were labeled depending on the obtained phase, F (faujasite) and M (ZSM-5), 1 for (Dimethyloctadecyl[3- (trimethoxysilyl)propyl] ammonium chloride (DMOTPAC) and 2 by using cetyltrimethylammonium bromide-polyethylene glycol (CTAB-PEG). The textural properties for supports exhibited a unimodal pore size distribution around 3.9 nm. The TEM images showed the formation of different structures and morphologies, depending on the type of sample. The TPD of NH3 results indicated a clear variation in the quantities of acid sites following the trend F2>F1>M2>M1. These materials were used to support Co-Mo sulfides and they were tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The CoMo catalysts showed the activities trend: CoMo/M1>CoMo/M2>CoMo/F1> CoMo/F2. This behavior resulted in agreement with length and stacking of MoS2 slabs as well as with the NO adsorption amount. The tendency displayed by the surface acidity resulted inverse to the HDS activity and also was inversely proportional to the length and stacking of MoS2 slabs. Thus, the highest the acid sites amount the lowest the slab length and stacking.