CoMo Catalysts Research Articles

Ammonia-free synthesis of Mo/CoMgAl catalysts with excellent activities in water-gas shift reaction

A series of CoMgAl mixed oxides with homogeneous Co dispersion were prepared using co-precipitation method. The CoMgAl composites were then doped with Mo species, giving Mo/Co(x)MgAl (x=Co/(Co+Mg)) catalysts for water-gas shift reaction (WGSR). In the synthesis of these catalysts, there is limited release of ammonia, which is traditionally common in the generation of Mo-Co catalysts for WGSR. The Mo/Co(x)MgAl catalysts were characterized using techniques such as XRD, N2-physisorption, H2-TPR, H2S-TPS, Raman, HRTEM and XPS. It is noted that the Mo/Co(5%)MgAl catalyst gives 91.2% CO conversion at 350 °C, which is close to the equilibrium CO conversion (91.7%). The H2S-TPS results disclose that there is decrease in activation energy for Mo sulfidation with increase of Co content in Mo/Co(x)MgAl, indicating the presence of Co promotes Mo sulfidation. The outcomes of HRTEM and XPS analyses reveal that the role of Co is to decrease stacking number and slab length of MoS2 moieties. The EDX elemental analysis suggests synergism between Co and MoS2, especially in the case of Mo/Co(5%)MgAl. With the formation of small-size MoS2 slabs and enhanced Co-MoS2 synergistic effect, the Mo/Co(5%)MgAl catalyst has high exposure of active sites, leading to improved catalytic activities in WGSR.

Comparison of γ and δ-Al2O3 supported CoMo catalysts in the hydrodesulfurization of straight-run gas oil

The effect of two different crystal species of alumina on hydrodesulfurization activity of the corresponding CoMo catalysts was studied. Cylindrical extruded alumina with two different crystal structures i.e. γ-Al2O3 and δ-Al2O3 was prepared using boehmite and nitric acid as a peptizing agent by calcination at 550 ˚C and 900 ˚C, respectively. The Al2O3 support were impregnated with 9 wt.% of Mo and 2 wt.% Co via incipient wetness impregnation method. The CoMo/Al2O3 catalysts were used for hydrodesulfurization (HDS) and hydrodenitrification (HDN) of Iranian straight-run gas oil (ISRGO). The supports and catalysts were characterized by nitrogen adsorption-desorption isotherm, XRD, UV-vis-DRS, TPD, TPR and ICP-OES. The HDS activity of CoMo/γ-Al2O3 catalyst was higher than that of CoMo/δ-Al2O3 and was found to be 95.74%. This result was due to the formation of larger CoMoO4 and MoO3 crystals in CoMo/δ-Al2O3 catalyst which reduces the active metal phase dispersion and the performance of the catalyst. The HDS activity of CoMo/γ-Al2O3 catalyst was remarkable as the metal content of the catalyst was low. The HDN activity of CoMo/γ-Al2O3 was also about 66%.

Catalysis performance of nonpromoted and co-promoted MoS2 catalysts on a hydrodesulfurization reaction: A DFT study

To elucidate the function of the metal Co in the hydrodesulfurization (HDS) process, a closed cycle mechanism, including generation/regeneration of sulfur vacancy, adsorption of thiophene and complete HDS reaction of thiophene (hydrogenation (HYD) and direct desulfurization (DDS) pathways), was investigated via density functional theory (DFT-D) calculations on pure MoS2 and Co-MoS2 catalysts. All possible products were taken into consideration; for example, both HYD and DDS pathways could produce four kinds of products (butadiene, 1-butene, 2-butene, and butane), while the HYD pathway on the S edge of 100% Co-MoS2 catalyst produced three of the same products without butane. From the functional analysis of Co, the Co promoter has changed the original reaction mechanism and related product distribution. The sulfur vacancy on the 50% Co-promoted S edge exhibited the most commendable HDS activity, and 2-butene is obviously improved. Whereas 50% of the Co-promoted Mo edge inhibits the HDS process, Co-doping in the Mo edge could limit its catalysis performance. The generation/regeneration of sulfur vacancies could be the rate-limiting step on the S edge of nonpromoted and Co-promoted MoS2 catalysts; however, it will not be the rate-limiting step on the Mo edge.

Effect of Carbonization on CoMoS Catalyst supports in the Hydrodeoxygenation of Guaiacol as a Model Bio-Oil Compound

CoMoS/Cx/Sup Catalysts were prepared using 12-molybdophosphoric heteropolyacid and cobalt citrate. The supports were Al2O3, SiO2, nos, ZrO2, and carbonized Cr/Sup derived substrates (2 and 6 mass % carbon). The catalytic properties of these samples in the hydrodeoxygenation of guaiacol in a microflow apparatus were studied. With increasing carbon content in the supports, the length and number of MoS2 layers in the package increase in all the samples, apparently due to a decrease in the strength of the particle interaction with the more inert carbonized surface. Furthermore, the dispersion of the molybdenum particles on the catalyst surface, the content of promoter in the CoMoS active phase, and the extent of promotion of the crystallite edges differ significantly. The reasons were examined for the observed behavior and possible activity interrelationship during the hydrodeoxygenation of guaiacol with the parameters of the catalyst and active phase nanoparticles.

Synthesis, application and kinetic modeling of CeOx–Si–CoMo catalysts for the hydrodesulfurization of dibenzothiophene

CeOx–Si–CoMo catalysts for efficient hydrodesulfurization (HDS) activity of dibenzothiophene: role of ceria in catalyst activity and product selectivity.

Effect of Co incorporation and support selection on deoxygenation selectivity and stability of (Co)Mo catalysts in anisole HDO

A series of supported Co modified Mo catalysts was prepared by varying the Co/Mo ratio in the range from 0 to 1 while maintaining the Mo loading at ca. 10 wt%. A sequential incipient wetness impregnation method, with Mo being introduced first, using aqueous solutions of the corresponding precursor salts was employed during the synthesis procedure. Three supports, i.e., Al2O3, ZrO2, and TiO2 differing in textural and acidic properties were investigated. Material physicochemical characteristics were evaluated through ICP-OES, N2-sorption, XRD, H2-TPR, NH3-TPD, O2-TPO, STEM-EDX and XPS techniques. The anisole HDO performance of these CoMo catalysts was evaluated at gas phase conditions in a fixed bed tubular reactor in plug flow regime. The catalysts performance is correlated with properties such as reducibility, acidity, and metal-support interactions. Cobalt addition enhanced the total HDO selectivity by 45% as compared to Mo catalysts. Alumina catalysts displayed higher initial activity (Xanisole≈97%) relative to titania and zirconia supported variants (Xanisole <40%) at identical operating conditions. Titania supported catalysts exhibited rather higher stability compared to zirconia and alumina catalysts over 50 h time on stream (TOS), while zirconia catalysts displayed the highest HDO selectivity (up to 86%). Characterization studies of pre and post-reaction catalysts indicate Mo5+ to be the main active phase while over-reduction to lower Mo states (Mo4+ and Mo3+) as well as carbon deposition are identified as the cause for catalyst activity decrease with TOS.

Effect of boron on the efficiency of MoCo catalysts supported on alumina for the hydrodesulfurization of liquid fuels

Abstract The effect of boron content on hydrodesulphurization (HDS) activity was investigated under different optimized conditions. γ-Al2O3 was loaded with MoCo and then doped with boron. The obtained materials, i.e. AlMoCoB0%, AlMoCoB2%, and AlMoCoB5% were characterized by N2-physisorption, X-ray diffraction, temperature programmed analysis by reduction and desorption, Fourier-transform infrared spectroscopy, a scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The catalytic activity of the prepared catalysts was evaluated for the HDS of dibenzothiophene (DBT) using a Parr batch reactor at T = 300 °C and under 50 bar hydrogen partial pressure. The textural properties of the prepared catalysts were enhanced by introducing the boron. For example, the BET surface area of AlMoCoB5% was 206 m2/g which is higher than that of both AlMoCoB0% and AlMoCoB2%. The acidity and dispersion AlMoCoB5% were 0.77 and 2.46 (mmol/g), respectively, which increase its HDS activity. The boron enhanced the particle dispersion, leading to an improvement in the catalytic activity of the MoCo catalysts in the elimination of sulfur content. Experimental factors (such as temperature, pressure, the dosage of the catalysts and contact time) were investigated and optimized using a central composite design. The results revealed that the HDS was improved by increasing the temperature, pressure, and catalyst dosage. The optimum contact time was found to be 6 h with a dosage of 0.6 g. The experimental results indicated that AlMoCoB5% has the highest HDS activity, achieving more than 98% of sulfur removal, which is below the allowed sulfur level. The excellent catalytic activity of the AlMoCoB5% catalyst in the HDS of DBT is particularly useful for the ultradeep HDS of fuels.

Forming Atom–Vacancy Interface on the MoS2 Catalyst for Efficient Hydrodeoxygenation Reactions

AbstractAtomically dispersed supported catalysts show superior catalytic activity and selectivity in diverse reactions, while the challenging part is identifying the active sites and revealing the reaction mechanisms, which play essential roles in rational design of efficient catalysts to massive energy consumption reduction. Herein, an atom vacancy interface (AVI) model is proposed, for the first time, based on a case study of atomically dispersed Co atoms distributed on 2H‐MoS2 surfaces as promising catalysts for hydrodeoxygenation (HDO) reactions. The results show that the reactive single Co atom promotes the H2 activation and leads to largely increased sulfur vacancies adjacent to the metals and the formation of metal vacancy interfaces on the MoS2 surface. Detailed reaction mechanism studies demonstrate that the AVI model is quite different from edge vacancy dominated unprompted MoS2 and traditionally prepared CoMoS2 catalysts. The novel structure results in a considerable reduction of energy barriers of three elementary steps including CO scission, hydrogenation processes, and catalytic center regeneration, and eventually boots the HDO reaction at low temperature.

Synthesis of molybdenum cobalt nanocatalysts supported on carbon for hydrodesulfurization of liquid fuels

The effects of activated carbon support on the characteristics and efficiency of CoMo catalysts in the dibenzothiophene hydrodesulfurization were studied. Catalysts of Mo and Co were made with and without loading on activated carbon (AC) to form ACMoCo and MoCo catalysts, respectively. The AC support was synthesized from waste automobile tires material. The metal species (Mo and Co) were loaded by wetness impregnation of the salt solutions of the respective metals. The prepared materials were characterized by N2-physisorption, temperature programmed analysis by desorption and reduction, X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy, inductively coupled plasma and Fourier transform Infra-red. The results indicated that ACMoCo showed a better performance in hydrodesulfurization starting with a model oil dibenzothiophene containing 500 ppm-S. 98.8% removal of the sulfur was achieved with ACMoCo compared to 73.5% for the MoCo under the same reaction conditions. The increased catalytic activity of ACMoCo catalyst in dibenzothiophene hydrodesulfurization can be explained by the nature of the catalyst support, which is of the high surface area and high acidity which attract the dibenzothiophene being of basicity nature. The analysis of the support on the catalyst activity was carried out based on the sulfur removal efficiency.

Facile production of biofuel via solvent-free deoxygenation of oleic acid using a CoMo catalyst

Support- and sulfide-free cobalt molybdenum catalysts are prepared via different synthetic procedures for catalytic deoxygenation of oleic acid under inert (N2) and solvent-free conditions. Among the tested catalysts, the CoMo catalyst prepared via a sol-gel method achieves the highest catalytic performance, namely, 88.9% oleic acid conversion, with 48.1% C9–C17 selectivity, and 69.6% oxygen removal rate, owing to its excellent physical properties. Additionally, oxygen vacancy is formed in CoMo catalyst during sol-gel synthesis process and it also effect on the catalytic activity. Examination of the deoxygenation reaction over pre-reduced catalysts reveals that the CoMoO4 species is the active species in the CoMo catalysts. The fuel properties of the resultant products are affected strongly by the catalytic performances of the CoMo catalysts. The biofuel produced using the CoMo catalyst prepared via the sol-gel method showed the highest calorific value (10,119 cal/g) and the lowest viscosity (31.5 cP), and, consequently, this CoMo catalyst exhibits the highest catalytic activity and has significant potential for application in biofuel production.

Triglycerides Hydrocracking Reaction of Nyamplung Oil with Non-sulfided CoMo/γ-Al2O3 Catalysts

The purpose of this research are to study the temperature influence in hydrocracking process of the nyamplung oil (Calophyllum inophyllum) using a non-sulfided CoMo/γ-Al2O3 catalyst and to develop a simple kinetic model in interpreting the data of hydrocracking products. The experiment was carried out in a pressurized batch reactor operated pressure up 30 bar. The CoMo catalyst supported with γ-Al2O3 was prepared through impregnation method without sulfidation process. The operating temperature varied from 200 to 350 oC. The results show that the non-sulfided CoMo/γ-Al2O3 catalysts, nyamplung oil triglycerides can converted into gasoil and gasoline-like hydrocarbons. The triglyceride hydrocracking reaction of nyamplung oil followed a several stages, i.e., hydrogenation, dehydrogenation, and cracking. Based on the compounds contained in liquid product, hydrocracking reaction was dominated by decarboxylation. The products obtained in hydrocracking process of nyamplung oil are classified to gasoil (C11-C18) and gasoline (C5-C10). The triglycerides hydrocracking reaction of nyamplung oil was assumed by following a series reaction mechanism and a simple kinetic model used for determined the kinetics constants. The highest reaction conversion is 99.10% obtained at temperature of 350 °C for 160 minutes reaction time.

CoMo Hydrotreating Catalysts Supported on Al2O3, SiO2 and SBA-15 Prepared from Single Co2Mo10-Heteropolyacid: In Search of Self-Promotion Effect

CoMo hydrotreating catalysts with varied metal loading (1–4 Mo at nm− 2) based on Co2Mo10 heteropolyacid (HPA) and different supports (γ-Al2O3, SBA-15, SiO2) were prepared by incipient wetness impregnation. The catalysts were characterized by N2 physisorption, high resolution transmission electron microscopy (HRTEM), Raman and X-ray photoelectron spectroscopy (XPS). Catalytic activity was evaluated in co-hydrotreating (HDT) of the model feed containing dibenzothiophene (DBT) and naphthalene. The catalytic properties of CoMo catalysts were shown to depend on the morphological characteristics of CoMoS species, its promotion degree, and metal loading. The sulfidation degree of the initial precursor and effective cobalt amount in the CoMoS species increased with the Mo loading increase from 1 to 4 at nm− 2 in all studied catalysts. The DBT conversion maximum was achieved over CoMo/Al2O3 and CoMo/SBA-15 with 4 Mo at nm− 2. CoMo/SBA-15 catalysts had higher TOF numbers both in DBT HDS and in naphthalene hydrogenation (HYD) at the surface concentration of Mo same as in the other samples. These results can be attributed to optimal morphology of sulfide particles and the Co/Mo promotion degree due to a more suitable interaction between the active phase and support in mesoporous silica channels.

Effect of partial Mo substitution by W on HDS activity using sulfide CoMoW/Al2O3–TiO2 catalysts

A series of Al2O3–TiO2-supported trimetallic CoMoW catalysts were prepared with the aim to study the effect of Mo substitution by W on the catalyst performance in deep hydrodesulfurization (HDS) reaction. The oxide catalyst precursors were characterized by N2 physisorption, temperature-programmed desorption of NH3 (TPD-NH3), temperature-programmed reduction (TPR), diffuse reflectance spectroscopy (DRS UV–vis) and Raman spectroscopy. Sulfided catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), and tested in the dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction carried out in a batch reactor at T = 320 °C and total H2 pressure of 5.5 MPa. It was found that partial substitution of Mo by W leads to enhancement of catalyst metal and acid functions. The W-rich catalyst (W/Mo atomic ratio of 1.2) exhibited the best catalytic behavior and a larger selectivity toward HYD route products than W-free CoMo counterpart. The catalyst structure-activity correlation suggested that this is due to the combined effects of the best dispersion of metal oxides, the enhance of the catalyst acidity, a lower stacking of Mo(W)S2 layers and the formation of mixed “Co–Mo(W)–S” phase. In contrast, the less active phase (CoMo2S4) was formed on the surface of the conventional CoMo catalyst. For all catalysts, The HDS reaction proceeds via direct desulfurization (DDS) and hydrogenation (HYD) reaction routes, the former being the main reaction route.

Tuning of diameter and electronic type of CCVD grown SWCNTs: A comparative study on Co-Mo and Co-Ru bimetallic catalyst systems

Wafer-level catalytic chemical vapour deposition (CCVD) of semiconducting enriched single-walled carbon nanotubes (sc-SWCNTs) with high quality is of high interest for industrial realization of SWCNT-based sensor and electronic applications. While bimetallic catalysts systems are known to favor type-enriched growth of SWCNTs, surface morphological evolution of different bimetallic catalyst stacks during catalyst conditioning as well as its impact on SWCNTs growth is not clearly understood. Here, we present a systematic study on the effect of bimetallic catalyst composition, layer stack thickness configuration as well as CCVD process parameters on the composition of grown SWCNTs. Besides the well-known Co and Co-Mo system, the Co-Ru system was investigated. We found that in case of Co-Mo bimetallic system, highest degree of sc-SWCNTs content is achieved using bilayer configuration Co-Mo:0.2–0.1 nm processed at 810 °C and 20 kPa total pressure. In case of Co-Ru bimetallic system, highest degree of sc-SWCNTs content is achieved using Co-Ru:0.1–0.1 nm processed at 840 °C and 10 kPa total pressure.

Cobalt-Molybdenum Single-Layered Nanocatalysts Decorated on Carbon Nanotubes and the Influence of Preparation Conditions on Their Hydrodesulfurization Catalytic Activity

Hydrodesulfurization (HDS) of crude oil plays a vital role in the refining of petroleum products. With ever-increasing regulations restricting the allowable concentrations of sulfur in fuel, further research is required to produce more efficient and effective catalysts. Herein, we have synthesized carbon nanotube (CNT)-supported cobalt-molybdenum (CoMo) catalysts for HDS of dibenzothiophene (DBT) via Co-first and Mo-first sequential impregnation as well as co-impregnation. Spectroscopic analysis shows the formation of a CoMo catalyst with no free sulfided Co phase present. Additionally, CoMo catalysts are found to be predominantly single-layered nanocatalysts layered on the CNT support. Temperature-programmed reduction (TPR) measurements show differences in reducing temperature of the sulfided CoMo catalysts prepared by the different methods, but catalyst activities for HDS of DBT did not fully align with the TPR-predicted order. Thus, provided the reaction temperature is high enough, reducibility may not...

Visualizing hydrogen-induced reshaping and edge activation in MoS2 and Co-promoted MoS2 catalyst clusters

Hydrodesulfurization catalysis ensures upgrading and purification of fossil fuels to comply with increasingly strict regulations on S emissions. The future shift toward more diverse and lower-quality crude oil supplies, high in S content, requires attention to improvements of the complex sulfided CoMo catalyst based on a fundamental understanding of its working principles. In this study, we use scanning tunneling microscopy to directly visualize and quantify how reducing conditions transforms both cluster shapes and edge terminations in MoS2 and promoted CoMoS-type hydrodesulfurization catalysts. The reduced catalyst clusters are shown to be terminated with a fractional coverage of sulfur, representative of the catalyst in its active state. By adsorption of a proton-accepting molecular marker, we can furthermore directly evidence the presence of catalytically relevant S–H groups on the Co-promoted edge. The experimentally observed cluster structure is predicted by theory to be identical to the structure present under catalytic working conditions.

Hydrogen and Carbon Nanotubes Production by Catalytic of Ethanol Over the Co-Mo Catalysts.

A series of Cobalt-Carbon, Cobalt-Molybdenum-Carbon catalysts were prepared by impregnation. The molar ratios of Co:Mo were 9:1, 8:2 and 7:3 and the total metal weights of them in the supported catalysts were 5 wt%. Moreover, the effects of reaction temperature and the Co:Mo molar ratios on the produce hydrogen and carbon nanotubes were investigated systematically. Of all the catalysts, Co-Mo (5 wt%, Co:Mo = 9:1)/C was the most effective one on the basis of hydrogen yield (84%), ethanol conversion (95%) and the quality of carbon nanotubes at 600 °C. A small amount of Mo added into the Co/C catalysts resulted in increasing in the yield of hydrogen and improving on quality of carbon nanotubes from ethanol decomposition over the Co-Mo catalysts.

Effect of structure and stability of active phase on catalytic performance of hydrotreating catalysts

For environmental protection and efficient utilization of oil resources, higher requirements for the selectivity, activity and stability of hydrotreating catalysts are proposed. To effectively solve this issue, the influence of structure and stability of active phase on catalytic performance of hydrotreating catalysts was reviewed. It was realized that the active phase structure essentially depends on the extent of metal-support interaction, and can be properly designed by adjusting catalyst preparation parameters (e.g. support properties and metal precursors in the impregnating solution) and sulfidation conditions (e.g. pressure, temperature and gas composition). As the hydrotreating conditions for gasoline, diesel and residue become severer, the active phase structures need much higher stability. The selectivity of gasoline hydrodesulfurization can be notably increased by selective post-treatment of the active phase structure. Well-dispersed active phase slabs with moderate metal-support interaction are needed for highly active and stable CoMo and NiMo diesel catalysts. New generation NiMo catalyst by strengthening metal-support interaction exhibits better residue hydrodesulfurization activity and stability.

Alumina-carbon nanofiber composite as a support for MoCo catalysts in hydrodesulfurization reactions

Developing more effective catalysts for the hydrodesulfurization (HDS) process has gained more importance in recent decades to produce ultraclean fuel. In the current study, a novel carbon nanofiber doped alumina (AlCNF) was prepared as a support for the MoCo catalyst for the HDS reaction of dibenzothiophene (DBT). The in-situ prepared composites were characterized by using Brunauer–Emmett–Teller (BET), temperature-programmed reduction (TPR) powder X-ray diffraction (XRD), scanning electron microscope (SEM), infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). The catalytic activity of the MoCo catalysts supported on nanofiber doped alumina (AlCNFMoCo) was tested and compared with the MoCo catalysts supported on alumina (AlMoCo). The AlCNFMoCo catalyst reduced the sulfur concentration in the liquid fuel down to below the allowed limit in a 6 h reaction time, showing a higher catalytic activity compared to AlMoCo. The improved catalytic activity of AlCNFMoCo can be explained by the high mesoporous surface area and the better dispersion of the MoCo metals on the AlCNF support compared to the alumina support. BET analysis indicated that the textural properties were improved by introducing CNF. The surface areas of AlMoCo and AlCNFMoCo were 166 and 200 m2/g. The SEM images indicated that the catalyst nanoparticles were well distributed on the surface of the CNF.

Reactivity of cyclohexene using ordered mesoporous materials based on calcined CoFeAl hydrotalcite-supported CoMo catalysts

Co2+, Fe3+ and Al3+ tertiary hydrotalcite-type solids were synthesized, calcined and impregnated with Mo (15 wt% MoO3) and Co (3Mo:Co) in order to get different catalytic precursors: CoMo/CoFeAl. As-synthesized hydrotalcites and their catalytic precursors were characterized by different physicochemical techniques, such as: X-ray fluorescence, N2 adsorption–desorption isotherms (BET specific surface area, BJH pore volume and diameter), Fourier transform infrared spectroscopy, X-ray diffraction and temperature-programmed desorption of carbon dioxide. These CoMo/CoFeAl catalytic precursors were previously pre-sulfided with CS2 and tested in the cyclohexene hydrogenation reaction. Results indicated that these sulfide catalysts showed very low activity in comparison with the conventional CoMo/Al2O3 catalyst used as reference, possibly to their high basicity. These catalysts could have the advantage of retaining the octane number of gasoline, by low hydrogenation of olefins.