NiMo Catalysts Research Articles

Thermal and Structural Characterization of Coke Deposition on Spent NiMo Catalyst Used During Catalytic Upgrading of Heavy Oil

Catalyst deactivation has become a major concern in the refining industry globally. The deactivation of hydroprocessing catalyst by coke deposition reduces its useful life, the on-stream time of the process involved and the profitability of upgrading heavy oils to useful products. There are various methods used in thermal and structural characterization but for the purpose of this research journal, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) were carried out on both fresh and spent NiMo catalyst. The TGA results of the spent catalyst samples indicates the presence of coke species with the major portion of the species being ‘medium’ and ‘hard’ coke (second and third stage). There was also no significant change in loss of weight with change in heating rate. In comparison to the fresh catalyst, the SEM micrograph of the used catalyst indicates the formation of poor porous-structure and block-shaped crystallites depicting the sintering of particles because of the higher calcination temperature. O–C–O bond stretching vibrations with an anatase morphology were observed using FTIR on the spent catalyst sample confirming the presence of the coke species while the XRD results showed the formation and nature of carbonaceous deposits on the spent catalyst’s surfaces. A rutile phase with a tetragonal symmetry was detected for spent NiMo diffraction peaks, with the major phase indicating the presence of Carbon with a hexagonal phase.

Pitfall on the interpretation of double layer capacitance increase after accelerated stress test of hydrogen evolution reaction on NiMo catalysts

Critical investigation of methods used to screen the catalytic activity of different electrocatalysts is crucial for the development of water electrolysis technology. One of such protocols to justify the catalytic activity trend among different catalysts involves determining their electrochemically active surface area (ECSA) which is usually estimated from non-Faradic double layered capacitance (Cdl) of the catalyst material. Furthermore, catalytic current normalized with ECSA is frequently used to gain insight into the intrinsic activity of a catalyst. Since not all the metallic catalysts are highly stable under the electrolysis conditions, it is highly important, though rarely explored, to investigate whether or not the adsorption/desorption of leached/dissolved multivalent metal ions influences the measurement of non-Faradic Cdl. Here, we explore the possible influence of Mo leached from NiMo alloy on the measured Cdl of NiMo. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), Cdl of NiMo alloy was measured before and after carrying out long term (chronopotentiometric and CV cycling) hydrogen evolution reaction (HER) in alkaline conditions. After extended HER testing, we observe a notable rise (∼22 % averaging all our experiments) in the Cdl of NiMo alloy when measured with traditional methods. Interestingly, only 8 % of this increase can be attributed to an expansion in surface area. We hypothesize that the majority of the increase in Cdl stems from the higher amount of charges stored through leached multivalent ions, which accumulate within surface cavities.

Revealing the Role of Mo Leaching in the Structural Transformation of NiMo Thin Film Catalysts upon Hydrogen Evolution Reaction.

NiMo alloys are considered highly promising non-noble Hydrogen Evolution Reaction (HER) catalysts. Besides the synergistic effect of alloying elements, recent attention is drawn to the Mo leaching from the catalyst. This work investigates the role of Mo in NiMo alloys during HER, aiming to understand the interplay between compositional, structural, and electronic factors on the activity, and their effects on the electrode material and catalyst properties. For this purpose, sputter-deposited low roughness NixMo100-x thin films are produced. The investigation of catalyst performance depending on their chemical composition shows a volcano-shaped plot, peaking for the Ni65Mo35 alloy with the highest intrinsic activity in alkaline HER. A comprehensive electrode surface analysis combining transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy identifies the leaching of Mo on a structural level and indicates the formation of a Ni(OH)2-rich surface area. The ultimate surface characteristics of the NiMo catalysts depend on the initial composition and the electrochemical procedure. Based on the findings, it conclude that the observed catalytic properties of NiMo alloys in HER are determined by a complex interplay of increasing roughness, available surface species and their synergies. The leaching of Mo has a proven structural effect and is considered one of several factors contributing to the enhanced catalyst activity.

Deoxygenation and isomerization activity balance for NiMo/ZSM-23 catalysts as an effect of Mo/(Ni+Mo) ratio in hydroprocessing of fatty acids

Series of Ni-Mo catalysts based on ZSM-23 zeolite were synthesized by incipient wetness impregnation – with a fixed content of Ni (5 wt. %). These catalysts were tested in a hydroprocessing of a mixture of fatty acids (C16-C18) in a flow reactor at a temperature of 300 °C, a pressure of 2.5 MPa and WHSV = 8.4 h-1. The influence of the ratio of metals on the formation of forms of the active component, as well as on the activity, selectivity to iso-alkanes and the stability of catalysts during the hydroprocessing of a mixture of undiluted fatty acids was determined. The ratio of metals was investigated in the range from 0 to 1. The highest deoxygenation activity and highest isoalkanes yield were found for sample with Mo/(Ni+Mo) ratio equal 0.25, in which, according to the XPS, the Mo/(Ni+Mo) ratio on the surface is 0.4.

Optimized spacing of active sites in Ni-Mo catalysts enhances ethanol production in syngas conversion

The direct conversion of syngas to ethanol is highly attractive but remains challenging due to low CO conversion and poor EtOH/ROH. We investigated the conversion of syngas over a KNiMo2C catalyst modified with carbon dots (CDs) derived from Ligustrum lucidum leaves. On the Ni0.54Mo-A catalyst, a CO conversion of 43.4 % was achieved, with oxygenates selectivity and EtOH/ROH，reaching 48.2 % and 63.7 %, the space-time yield of ethanol was 132.5 mg/gcat/h. Comprehensive characterization revealed that CDs regulate the distance between Ni-Mo active sites, preventing excessive proximity and maintaining an optimal separation. This adjustment significantly enhances EtOH/ROH by modulating the probability of carbon chain growth. A potential new reaction pathway for directly converting syngas to ethanol is proposed, The C-C coupling of CHx* with *COOH or *CO2 is identified as a key step in carbon chain growth. This work provides a new catalytic pathway for the syngas to ethanol industry.

Efficient conversion of used palm cooking oil into biogasoline over hydrothermally prepared sulfated mesoporous silica loaded with NiMo catalyst

Fossil-based fuels remain a primary global energy source, but their finite and non-renewable nature raises concerns about long-term sustainability. These issues underscore the urgent need for renewable and eco-friendly alternatives such as converting vegetable oil into biofuel. The present work reported biogasoline production from used palm cooking oil catalyzed by sulfated mesoporous silica impregnated with nickel-molybdenum bimetal using the hydrothermal method for both steps. We evaluated the effect of sulfuric acid concentration and metal loading amount on the acidity of the resulting catalysts. Catalysts' performance was assessed through the catalytic cracking and hydrocracking processes with a catalyst-to-feed ratio of 1 % at 550 °C and an atmospheric pressure. In comparison to mesoporous silica (MS) and sulfated mesoporous silica (SMS-2), along with an increase in acidity, NiMo-impregnated mesoporous silica (NiMo 1/SMS-2) exhibited superior catalytic performance in biogasoline production in the presence of H2 gas, achieving liquid product conversion and gasoline selectivity of 55.9 % and 52.37 %, respectively. These results are an excellent step for developing biogasoline in a safer process and confirm the capability of mesoporous silica-based catalysts in biofuel production.

Bimodal mesoporous AlMCM-41 supported NiMo catalysts for efficient hydrodesulfurization of 4,6-dimethyldibenzothiophene

In this research, a bimodal mesoporous AlMCM-41 (B-AM41) material was prepared and applied to support NiMo catalysts for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene. Additionally, catalysts supported on smaller and larger single-pore AlMCM-41 (S-AM41 and L-AM41) were also prepared as reference catalysts. Detailed characterizations show that the proportion, stacking degree, and length of the MoS2 active phase on the different catalysts are distinct. As a result, HDS evaluation indicates that the NiMo/B-AM41 catalyst exhibited better catalytic activity with a reaction rate constant of 10.4 × 10−8 mol g−1 s−1 and a turnover frequency of 7.0 × 10−4 s−1, significantly surpassing the S-AM41 and L-AM41 supported catalysts. The superior activity of the NiMo/B-AM41 catalyst can be attributed to a high sulfidation degree that provides sufficient highly dispersed type Ⅱ MoS2 phases with minimal stacking and moderate slab length. Moreover, the bimodal mesoporous structure promotes the diffusion of 4,6-DMDBT and benefits its contact with active sites.

Efficient Catalytic Hydrocracking of Crude Palm Oil Over EDTA Template-assisted SiO2-Al2O3/NiMo Catalysts

The development of hydrocracking catalysts for crude palm oil (CPO) is a challenging process due to its limited textural or pore accessibility and low acidity properties. Therefore, this study aims to develop a series of SiO2-Al2O3-x/NiMo catalysts using different Al mass (x = 5, 10, 25 g) assisted with EDTA to enhance their physicochemical properties. During the procedures, bimetallic NiMo species were dispersed into SiO2-Al2O3-x using the wet impregnation method. The structural, textural, surface morphology, particle size distribution, and acidity properties of the products were then assessed. Catalytic activity of catalysts on hydrocracking of CPO was evaluated at 350 °C for 2 h, H2 gas pressure of 20 bar, and mixed at 1500 rpm. The results showed that increasing Al mass caused an increment in the total acidity, acid site density, and surface area of SiO2-Al2O3-x. In addition, SiO2-Al2O3-25 provided better support properties, allowing preferable NiMo dispersion. Hydrocracking assessment showed that CPO conversion was increased at higher Al mass, producing the highest bio-aviation and biogasoline fractions yield. Based on these results, SiO2-Al2O3-x/NiMo successfully enhanced CPO conversion of unloaded SiO2-Al2O3-x, as well as increased the yield of bio-aviation and biogasoline fractions.

Linking Ab initio density functional theory with modelling reaction microkinetics to understand catalytic fatty acids hydro-deoxygenation intermediate species selectivity

Catalyst surfaces enable the catalytic reactions via binding of substrates and lowering the reaction barriers to obtain the desired products. Separating the binding process from the reaction barriers enables us the understanding of surface properties and enables the reaction engineering strategies such as choice of solvents or functional groups protections. Through the modelling of the hydrodeoxygenation (HDO) of fatty acids, namely Stearic, Oleic, Linoleic, Myristic and Decanoic acid we show why the alkanes are the ideal solvent choice for NiMoS catalyst, why the alcohols side products form, regardless of the kinetic constant indicating fast dehydration, why the aldehydes intermediates are rarely detected and why hydrogenation of double bonds supersedes other kinetics events. We confirm the DFT calculations by integrating them into the kinetic model which confirms that the obtained results are sensible and usable in reaction engineering. The results are supported by the detailed characterization of the NiMoS catalyst.

Renewable Diesel Production over Mo-Ni Catalysts Supported on Silica

Nickel catalysts promoted with Mo and supported on silica were studied for renewable diesel production from triglyceride biomass, through the selective deoxygenation process. The catalysts were prepared by wet co-impregnation of the SiO2 with different Ni/(Ni + Mo) atomic ratios (0/0.84/0.91/0.95/0.98/1) and a total metal content equal to 50%. They were characterized by XRD, XPS, N2 physisorption, H2-TPR, and NH3-TPD. Evaluation of the catalysts for the transformation of sunflower oil to renewable (green) diesel took place in a high-pressure semi-batch reactor, under solvent-free conditions. A very small addition of Mo, namely the synergistic Ni/(Ni + Mo) atomic ratio equal to 0.95, proved to be the optimum one for a significant enhancement of the catalytic performance of the metallic Ni/SiO2 catalyst, achieving 98 wt.% renewable diesel production. This promoting action of Mo has been attributed to the significant increase of the metallic Ni active phase surface area, the suitable regulation of surface acidity, the acceleration of the hydro-deoxygenation pathway (HDO), the creation of surface oxygen vacancies, and the diminution of coke formation provoked by Mo addition.

Preparation of presulfided oil-soluble NiMo catalyst for slurry bed hydrocracking of vacuum residue

Here, a method is proposed for constructing presulfided oil-soluble NiMo catalysts using tetrathiomolybdate nickel ammonium as a precursor via a chelating ligand exchange strategy. Leveraging the close chemical bonding between Ni and Mo atoms, the NiMo catalyst can undergo in-situ self-sulfidation to generate active NiMoS sites and a composite structure of Ni3S2 and MoS2 nano phase in tight contact, thus exhibiting strong synergistic effects. The NiMo catalyst exhibited outstanding performance in hydrocracking of vacuum residue (VR) achieving a 64.7 wt% VR conversion while maintaining a coke yield of 0.51 wt%, as well as the excellent hydrogenation activity of polycyclic aromatic hydrocarbons. Combined with density functional theory calculations, it was further revealed that the presence of Ni reduces the energy barrier for H2 dissociation on MoS2, thereby enhancing the hydrogenation activity of the catalyst and its ability to suppress coke formation. This work validates the efficient bimetallic synergistic catalytic effect of presulfided oil-soluble NiMo catalysts in the slurry bed hydrocracking process.

Impact of lanthanum ion exchange and steaming dealumination on middle distillate production using nanosized Y zeolite catalysts in hydrocracking reactions.

In the field of hydrocracking reactions, achieving optimal middle distillate yields remains a persistent challenge with commercially available zeolite Y catalysts. This limitation is attributed to challenges related to diffusion constraints within the catalyst. In response, we present a promising solution not only to these problems but also to the challenges encountered in nanosized Y zeolites when attempting to generate acidic sites within their structure and when analyzing their performance in vacuum gas oil hydrocracking. NiMo catalysts based on nanosized Y zeolites with different crystal sizes exchanged with lanthanum, effectively address diffusion issues and significantly enhance catalyst performance compared to dealuminated nanosized and commercial Y zeolite under the same reaction conditions. The catalysts were characterized by TGA, ICP-OES, XPS, N2 physisorption, FT-IR for pyridine acidity, TEM-mapping, and the 3-methyl thiophene reaction to test the hydrogenating capacity. Surface analysis and microscopy showed greater porosity in the catalysts with smaller zeolites and different arrangements of their components. The catalysts based on steamed protonated nanosized Y zeolites with a larger size and lanthanide nanosized Y zeolite with a smaller size yielded more middle distillates. Research provides a comprehensive analysis, providing a correlation between the catalytic performance and the size of the nanosized Y zeolite.

Heterogeneous Structure of Ni-Mo Nanoalloys Decorated on MoOx for an Efficient Hydrogen Evolution Reaction Using Hydrogen Spillover.

Herein, a heterogeneous structure of Ni-Mo catalyst comprising Ni4Mo nanoalloys decorated on a MoOx matrix via electrodeposition is introduced. This catalyst exhibits remarkable hydrogen evolution reaction (HER) activity across a range of pH conditions. The heterogeneous Ni-Mo catalyst showed low overpotentials only of 24 and 86, 21 and 60, and 37 and 168mV to produce a current density of 10 and 100mAcm-2 (η10 and η100) in alkaline, acidic, and neutral media, respectively, which represents one of the most active catalysts for the HER. The enhanced activity is attributed to the hydrogen spillover effect, where hydrogen atoms migrate between the Ni4Mo alloys and the MoOx matrix, forming hydrogen molybdenum bronze as additional active sites. Additionally, the Ni4Mo facilitated the water dissociation process, which helps the Volmer step in the alkaline/neutral HER. Through electrochemical analysis, in situ Raman spectroscopy, and density functional theory calculations, the fast HER mechanism is elucidated.

Applicability of Non-PGM Bi-Functional Electrocatalyst in a Scaled-up Anion Exchange Membrane Water Electrolysis

While non-precious metal catalyst materials are crucial for AEMWE systems, catalyst substances possessing both adequate hydrogen molecule adsorption ability and suitable electrical conductivity and hydrophilicity are still in the developmental stage.Ni-Mo alloy metals are known as those that have appropriate hydrogen molecule adsorption binding energy, making them excellent electrochemical catalysts for the cathode. However, they suffer from a high content of oxide, which hampers electrical conductivity, and the formation of a high oxidation state of Ni molecules, making hydrogen molecule detachment challenging.On the other hand, Ni-Fe alloys are recognized for their excellent -OOH group adsorption ability and high electrical conductivity, and that has a low oxidation state Ni phase for high hydrogen desorption ability.Therefore, in this study, we aimed to synthesize NiMoFe-based alloy catalysts to enhance the hydrogen evolution reaction (HER) activity of Ni-Mo group catalysts while simultaneously increasing the oxygen evolution reaction (OER) activity. Using a hydrothermal synthesis method for NiMoFe catalysts we employed a high-temperature thermal reduction process to minimize the oxide layer that has poor conductivity.Evaluation of the catalyst activity through half-cell experiments demonstrated low overpotentials in both Overall water electrolysis reactions. Furthermore, an MEA-type experiment was conducted to evaluate the applicability of single-cell.Furthermore, Stability tests confirmed a stable voltage.Finally, when compared to the combination of precious metal catalysts, this exhibited superior performance. Therefore, this study suggests that non-noble catalysts could serve as a crucial stepping stone, surpassing PGM metal catalysts in alkaline media.

Inhibiting effects during the co-conversion of lauric acid and anisole over Ni and NiMo catalysts

The co-hydroconversion of lauric acid and anisole was carried out over Ni and NiMo catalysts T=260 and 280 °C and pH2=40 bar. Ni/Al2O3 demonstrated a high activity in converting anisole to cyclohexane, but lauric acid conversion was suppressed over this catalyst. In the co-conversion of their mixture the phenolic had no effect on the conversion of the acid, but the latter prevented the cleavage of the C-O bond in both anisole and reaction intermediates. It was assumed that the successful conversion of anisole in its mixture with lauric acid required that a catalyst should provide the fast consumption of the acid component. Accordingly, NiMo/Al2O3 possessed a high activity in lauric acid conversion, and a high cyclohexane yield from anisole was observed after the complete consumption of the acid. The results of the present study can be useful for the rational design of a catalyst for the effective hydroconversion of bio-oil.

Efficient NiMoS electrocatalyst for alkaline hydrogen evolution reaction

In this work, cauliflower-like amorphous NiMoS catalysts were synthesized on nickel foam through cyclic voltammetry (NiMoSx@NF, x = 0.015, 0.030, and 0.045). The catalysts exhibited excellent electrocatalytic performance for the hydrogen evolution reaction (HER) in an alkaline environment. The synthesized NiMoS0.030@NF electrode achieved a current density of 100 mA cm−2 at an overpotential of 141.3 mV (vs reversible hydrogen electrode) in 1 M KOH (pH = 14) and displayed a Tafel slope of 77 mV dec-1. It can be attributed to the amorphous structure of the catalyst and appropriate electron cloud density. The work highlights the potential of the synthesized NiMoS0.030@NF electrode as an efficient electrocatalyst for the alkaline HER.

Effect of Pore Structure on the Performance of Mo-Ni Catalysts for Petroleum Resin Hydrogenation

Effect of Pore Structure on the Performance of Mo-Ni Catalysts for Petroleum Resin Hydrogenation

Insights into the role of Mo in boosting CHx* oxidation for CO2 methane reforming

CHx* oxidation is one of the most vital routes to alleviate the carbon deposition problem of CO2 reforming of methane (DRM) reaction. Whereas, little experimental evidence has been observed on NiMo catalysts where the CHx* oxidation was dominant over its dissociation reaction. Herein, to experimentally unveil the CHx* oxidation route of NiMo catalysts, we design three catalysts with different particle sizes and structures. Among them, Mo/Niphy@SiO2 core shell catalyst demonstrated the dominant CHx* oxidation route over its dissociation based on in-situ diffuse reflectance infrared Fourier transform spectroscopy experiments. This was attributed to the confinement effect of SiO2 and the formation of Ni–Mo alloy, inhibiting the CHx* dissociation reaction. It exhibited relatively stable CH4 and CO2 conversions (77 % and 75 % respectively) within 180 h. By contrast, on Mo/Niphy catalyst which has a big Ni size, CHx* was mainly dissociated to C* and oxidized to CO which further underwent a disproportion reaction to produce CO2 and C*, leading to the severe carbon deposition and unstable DRM performance. The strategy to unveil the dominant role of CHx* oxidation via design catalysts with different sizes and structures sheds light on the study of reaction mechanism of other reactions.

Highly selective hydrodeoxygenation catalyst for sustainable aviation fuel production from used cooking oil

The production of Sustainable Aviation Fuel (SAF) utilizing used cooking oil (UCO) as a renewable bio-waste resource holds immense potential for promoting sustainability in the aviation sector. In this study, SAF synthesis via hydrodeoxygenation of pretreated UCO over Ni-Mo/alumina-silica catalysts followed up hydroisomerization of deoxygenated oil has been investigated in a fixed-bed reactor. The effect of Al2O3/SiO2 ratio on the physico-chemical properties of Al2O3-SiO2 support and on the overall hydrodeoxygenation performance of the Ni-Mo catalyst supported on Al2O3-SiO2 has been investigated. NiMo catalyst supported on Al2O3-SiO2 in a 70:30 ratio achieved 86.69 % UCO conversion during the hydrodeoxygenation step and exhibited 74.79 % jet range hydrocarbon fuel selectivity under mild conditions (350°C, 1.1 h⁻¹ WHSV, 6 MPa, H2/oil (v/v): 400). The catalyst activity remained stable for >100 hours highlighting its good stability under the experimental conditions investigated. This work demonstrates the potential of tailor-made supported catalysts for highly selective single-step conversion of UCO into jet-range hydrocarbons, offering a significant step towards the production of sustainable aviation fuels.

Promoting Effect of Ce and La on Ni-Mo/δ-Al2O3 Catalysts in the Hydrodeoxygenation of Vanillin.

A crucial aspect of adding an economical and environmental dimension to the upgrading of bio-oils is to develop catalysts with enhanced and prolonged activity. In the present study, the effect of doping δ-alumina (Al2O3) with oxides of cerium (Ce) and lanthanum (La) before thermal treatment was investigated. The performance of such an Al2O3-supported nickel-molybdenum (Ni-Mo) catalyst was evaluated by studying the selectivity for the direct hydrodeoxygenation (HDO) of vanillin to cresol under continuous-flow conditions. In addition, the effect of adding H2S during catalyst activation and/or performance tests was also evaluated. Overall, enhanced performance of the doped NiMo catalyst in the HDO process has been demonstrated and an increased selectivity for cresol via direct HDO observed. The advantage of adding La and Ce is supported by the characterization results, where less sintering and enhanced pore diameter of the doped Al2O3 were observed after thermally inducing the transformation from the δ to θ phases. The improved characteristics and prolonged activity of the doped Al2O3 were also deduced by the lower acidity of the catalyst, which resulted in reduced coke formation during the HDO process.