Fe-Mo Catalyst Research Articles

A novel preparation strategy for an oil-soluble catalyst in slurry phase hydrocracking: Synergistic effect and electronic regulation of Fe on MoS2

The appropriate electronic structure of catalysts is vital for the slurry phase hydrocracking activity of inferior vacuum residue. Herein, a series of chemically bonded oil-soluble bimetallic FeMo catalysts with excellent performance were prepared by a novel strategy. Both experimental and density functional theory (DFT) calculations were conducted to investigate the regulatory effect of Fe on MoS2. It was found that the incorporation of Fe can reduce the average length and stacking layers of the MoS2 catalyst by 16.7% and 20.0%, respectively, thus exposing more active sites. Meanwhile, XPS, Raman and EXAFS results show that Fe transfers electrons to Mo to form electron-rich MoS2 and generate more defect sites on the surface of the FeMoS catalyst. For the VR hydrocracking activity test, it was demonstrated that the electron-rich MoS2 catalyst exhibits excellent performance, with the coke yield reduced by 32.0% and the total conversion rate of resin and asphaltene increased by 13.5%. Moreover, DFT results further reveal that the electrons transfer from Fe to Mo induces the change of chemical properties of the MoS2 surface and the adjustment of the d-band center, which promotes the migration of H and reduces the generation energy of coordinatively unsaturated sites. This study provides valuable insights into the design and upgrading of prominent oil-soluble bimetallic catalysts for slurry phase hydrocracking.

Effectiveness Study of Mesoporous Size, Acidity, and Precursor Type on Characterization of Activated Carbon as an Fe–Mo Catalyst Support for Hydrodesulfurization of Heavy Naphtha

Effectiveness Study of Mesoporous Size, Acidity, and Precursor Type on Characterization of Activated Carbon as an Fe–Mo Catalyst Support for Hydrodesulfurization of Heavy Naphtha

Boosting the electrochemical O2-to-H2O2 synthesis by revamping the FeMo catalyst with N/O co-doped surface

In electrochemical O2-to-H2O2 synthesis, the lack of systematic strategies and proof-of-concept studies is one of the key problems for practical applications. Herein, as exemplified by the FeMo bimetallic material for a two-electron oxygen reduction reaction (2e- ORR), we report a substantial improvement by facilitating the surface reconstruction of oxides or nitrides into N/O co-doped electrocatalyst. Additionally, in-depth evidence including electrochemical signals, H2O2-proof work, in-situ Raman and density functional theory (DFT) calculations, identified that the N/O co-doped FeMo catalyst has been favored by 2e- ORR, opening an effective pathway to the design of more bimetallic catalysts for electroreduction of O2 to H2O2.

X-ray absorption spectroscopic study of the alumina supported Fe and FeMo catalysts for methane dehydrogenation

Nanoscale Fe (5%Fe/Al2O3) and FeMo (4.5%Fe-0.5%Mo/Al2O3) catalysts are prepared by precipitating metal components onto alumina and then reducing in hydrogen at 700 °C for 2 hrs. The catalysts are characterized before and after their exposures to methane at 700 °C, employing ex-situ X-ray absorption spectroscopy (XAS) and X-ray diffraction techniques. XAS data of the as-prepared catalysts shows that, iron precipitates onto alumina as 6L-ferrihydrite, and Mo is present as molybdate (Mo(VI)O42-). The molybdate, which binds the alumina in the as-prepared FeMo catalyst, is partially reduced to MoO2. The reduction of iron to metallic state is incomplete because the ferrous iron binds the alumina, forming hercynite. After several hrs of methane exposure to both the catalysts at 700 °C, a major Fe3C and a graphite phase are observed only in the FeMo catalyst. The observation confirms that the Mo promotes more iron to an active Fe metal, a part of that metal converts to Fe3C and austenite (FexC). Concurrently, the MoO2 converts to Mo-oxycarbide (MoOxCy), the latter then carburize to Mo2C in the FeMo catalyst. The Fe metal, Mo-oxycarbide and metal carbides are mainly responsible for the conversion of methane to H2 and carbon. At reaction temperature > 900 °C, the Mo carbide particles agglomerate, and the excess carbon deposits on this agglomerate leading to catalyst deactivation. The deactivated catalyst is regenerated with CO2 treatment at 1000 °C to restore its initial oxide structure.

Spin regulation for efficient electrocatalytic N2 reduction over diatomic Fe-Mo catalyst

Electrocatalytic nitrogen reduction reaction (eNRR) is a promising method for the sustainable production of ammonia as an alternative to the traditional energy-intensive Haber-Bosch process. In this work, an efficient strategy by atomic spin regulation to promote NRR through Fe-transition metal (TM) hybrid heteronuclear dual-atom catalysts has been studied. By means of DFT computations, the stability, activity, and selectivity of 30 kinds of Fe-based dual-atoms anchored on N-doped porous graphene are systematically investigated to evaluate their catalytic performance. Fe/MoNC is screened as an excellent NRR catalyst with the limiting potentials of 0.63 V, and also suppresses HER. In the Fe/MoNC, the neighboring Fe atom regulates the spin state of the Mo center in MoN4 from high-spin state (2.63 μB) to medium-spin state (0.74 μB), which can effectively relieve the strong overlapping between Mo 4d orbital with the NxHy intermediates, promote the desorption of reaction product, and eventually achieve a lower limiting potential. Interestingly, the archetype of the active center of nitrogenase is also a FeMo-cofactor, which is consistent with our screening results. The work may provide new insight into the mechanism of nitrogenase, and promote the rational design of efficient NRR catalysts by atomic spin regulation.

Single-step synthesis of graphene nanosheets-carbon nanotubes hybrid structure by chemical vapor deposition of methane using Fe-Mo-MgO catalysts

A set of Fe-Mo-Mg catalysts with varying Mo/Mg weight ratios (40/10, 30/20, 20/30, and 10/40) were prepared and evaluated for the synthesis of graphene nanosheets/carbon nanotubes (GNS/CNT) hybrid materials via methane chemical vapor deposition. The results showed that changing the Mo/Mg ratio had a significant impact on the yield and the nature of the deposited carbon. The XRD and TPR results revealed that the iron molybdate and magnesioferrite species were the main components of Fe-Mo-Mg catalysts. TEM images showed that GNS-CNT hybrid materials were successfully grown on the surface of all Fe-Mo-Mg systems, except for the catalyst with the Mo/Mg ratio of 10:40, which produced CNT only. Raman spectroscopy results revealed that all carbon products were of high quality, with ID/IG ratios ranging from 0.14 − 0.41. It was also noticed that increasing the MgO content in the catalyst composition increases the amount of CNT compared to GNS. The total carbon yield increased from 170% to 284% for Fe-40Mo-10Mg and Fe-10Mo-40Mg, respectively. The gradual incorporation of Mg into the Fe-Mo catalyst significantly increased catalytic growth activity due to the presence of numerous mixed oxide species with diverse structures, such as MgFeOx, MgMoOx, and FeMoOx.

Unveiling remarkable resistance to Pb poisoning over an Fe–Mo catalyst for low-temperature NH3-SCR: poison transforms into a promoter

A heavy metal-resistant NOx catalytic reduction Fe–Mo catalyst was developed and a novel intrinsic activity enhancement mechanism by Pb species was originally demonstrated.

Guard-bed catalyst: Impact of textural properties on catalyst stability and deactivation rate

An effects of the hierarchical pore structures or pore type on guard bed catalyst during heavy oil hydroprocessing. • FeMo/Carbon-Al 2 O 3 supported catalysts with different texture were investigated for HDM. • An increase in porosity leads to higher HDM and metal retention capacity. • HDM relationship has been established with the type of pores. • Correlation between pore size distribution and HDM activity has been established • Micro- and mesopore showed a negative impact on HDM activity while macro-pores have a positive effect The hydrodemetallization (HDM) activity and the stability of FeMo supported catalysts have been investigated during the hydroprocessing of heavy crude oil. The prototype FeMo catalysts were developed in this study as guard-bed catalysts. Such type of front catalyst is frequently used in complex hydrotreatment to protect the more vulnerable subsequent catalysts. Various prototype supports were synthesized in this study to produce different textural properties. Such textural properties were generated and optimized by using different support compositions (0−75 wt.% activated carbon in alumina) and following a certain support pretreatment methodology for pore expansion. Both the support composition and the pretreatment methodology have significantly contributed in developing an optimized HDM catalyst with a large pore volume and a distinctive bimodal pore structure. The large pore volume substantially improved the metal retention capacity, while the bimodal pore structure remarkably reduced the diffusion limitation, allowing the large hydrocarbon molecules ( i.e. , asphaltene) to reach the inner catalytic sites to enhance their conversion rates. The presence of carbon in the catalyst support, even after calcination, considerably reduced coke and metal depositions on pore-mouths and catalytic sites. The textural and the mechanical properties of support indicate that the optimum composition is attained when the carbon-alumina ratio is 1:1 (50/50 wt.%). The role of textual properties on catalyst stability was investigated by comparing fresh and spent catalysts. The characterization of spent catalysts indicates that the bimodal type of pore has stable performance with time-on-stream (TOS).

Structure, functional composition and electrochemical properties of nitrogen-doped multi-walled carbon nanotubes synthesized using Co–Mo, Ni–Mo and Fe–Mo catalysts

We studied the effect of Co–Mo/MgO, Ni–Mo/MgO, and Fe–Mo/MgO catalysts on the structure and functional composition of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) synthesized by chemical vapor deposition method. Polyoxomolybdates containing Co–Mo, Ni–Mo, Fe–Mo сores were used as the catalyst precursors and acetonitrile was the source of carbon and nitrogen for the growth of N-MWCNTs in argon atmosphere at 900 °C. The Ni–Mo/MgO catalyst promoted the formation of N-MWCNTs with the smallest outer diameter of 8 nm and the highest content of embedded nitrogen of 2.7 at.% with a predominance of pyridinic nitrogen form. Co–Mo/MgO and Fe–Mo/MgO catalysts yielded thicker N-MWCNTs with an average outer dimeters of 12 and 15 nm and lower nitrogen content of 2 and 1.5 at.%, respectively. N-MWCNTs were tested as electrodes in electrochemical capacitors and Li-ion batteries. A higher efficiency of the N-MWCNTs synthesized using Ni–Mo/MgO catalyst confirmed the advantage provided by a high content of nitrogen in the nanotube walls.

Effect of Mo addition on the microstructure and catalytic performance Fe-Mo catalyst

Fe-Mo catalyst with different molar ratios (1:0, 1:0.5, 1:1, 1:2, 1:3) were prepared by chemical co-precipitation method, and they were added to phenolic resin as catalysts. The microstructure and physicochemical properties of catalyst and crystalline carbon after phenolic resin pyrolysis were characterized by XRD, SEM, FT-IR, XPS and TEM. The results showed that the Fe/Mo molar ratio played a significant role in the graphitization of phenolic resin and the morphology of carbon nanotubes. The graphitization of the phenolic resin first increased and then decreased with the addition of Mo. When the Fe/Mo molar ratio was 1:2, the phenolic resin achieved the highest graphitization, and the formed carbon nanotubes had the highest crystallinity. The Fe atoms were in an electron-deficient state due to the electrons transferring from Fe to Mo, which enhanced the hydrocarbon compounds absorption on the surface of catalyst. And Mo was carbonized by carbon atoms to form α-MoC1-x, and then decomposed into β-Mo2C and graphite carbon, obtaining carbon atoms orderly arrangement and carbon nanotubes. Therefore, both the grain size and electron structure of catalyst significantly affect the catalytic properties of Fe-based catalyst.

Effect of synthesis pH on the structure and catalytic properties of FeMo catalysts.

The effect of pH on polynuclear molybdenum species (isopolymolybdates) synthesis was investigated by Raman spectroscopy. As the pH decreased from 6.0 to 1.0, the main isopolymolybdates changed from MoO42− to Mo7O246− to Mo8O246− to Mo36O1168−. They began to aggregate and their solubility decreased with decreasing pH. The FeMo catalysts comprised particle- and plate-like structures, which were Fe2(MoO4)3 and MoO3, respectively. When a low pH value was used in the catalyst preparation, there was severe aggregation of the particles which have a high Mo/Fe mole ratio and Mo enrichment on the surface layer, which decreased the activity and selectivity of the FeMo catalyst.

Production of nanostructured carbon materials using Fe–Mo/MgO catalysts via mild catalytic pyrolysis of polyethylene waste

A series of MgO supported bimetallic Fe–Mo catalysts with various Fe:Mo weight ratios (such as 50:0, 45:5, 40:10, 30:20, 20:30 and 10:40, respectively) have been prepared and evaluated for production of carbon nanomaterials (CNMs) via catalytic pyrolysis of low-density polyethylene (LDPE) plastic waste. Highly acidic HZSM-5 zeolite was used as a degradation catalyst during the pyrolysis process. To investigate the structure and physicochemical properties of the fresh catalysts, several characterization tools such as XRD, TPD, BET, TPR, and FTIR were employed. While to clarify the nature and morphology of as-produced CNMs, the spent catalysts were characterized by XRD, TEM, Raman spectroscopy and TPO. The XRD and TPR results confirmed that the non-interacted metal oxides species were dominant in the structure of the catalysts with higher Fe2O3 or MoO3 contents, whereas several mixed oxide species were extensively present in the catalysts with moderate Fe2O3 and MoO3 contents. The obtained results revealed that the Fe/Mo ratio was found to play a crucial role on the catalytic growth activity as well as the type and morphology of as-deposited CNMs. All results showed that the type and morphology structure of carbon deposited can be adjusted by changing the Fe/Mo ratio in the MgO support. The activities of catalysts were significantly improved with the successive addition of Mo contents up to 30 wt% due to the presence of a large number of diverse active sites as a result of interaction between all catalyst components. The catalysts with higher Fe or Mo contents promote the formation of both CNTs and CNFs, while the catalysts with intermediate loadings of Fe and Mo produce mainly CNTs, CNFs accompanied with GNSs as hybrid materials.

Acrolein production from methanol and ethanol mixtures over La- and Ce-doped FeMo catalysts

The acrolein production from methanol and ethanol mixtures over iron-molybdate-based catalysts was studied. The reaction to acrolein can be described by two successive steps: the first consists on the oxidation of both alcohols into their corresponding aldehydes and the second step is the subsequent aldol condensation of the as-formed aldehydes. The iron-molybdate catalysts were modified by doping with La and Ce (1%mol) in order to improve the aldol condensation step of the process. Series of catalysts were thus synthesized with different Mo/Fe ratios (i.e., 1.5, 2.0 and 2.5) and calcined at three different temperatures (i.e, 350 °C, 400 °C and 450 °C). The best catalytic performance was observed for FeMoCe2.0 (400 °C) for which the acrolein yield reached 42% (T = 320 °C, MetOH/EtOH = 1, GHSV = 3900 h−1). Furthermore, all the samples were characterised by TGA-DSC, HT-XRD, XPS, BET, LEIS, XRF, CO2-TPD, Pyridine (FTIR) and NH3 (calorimetry) adsorption. The increase in acrolein yield observed upon La and Ce doping was attributed to acid/base properties modification.

Fe–Mo and Co–Mo Catalysts with Varying Composition for Multi‐Walled Carbon Nanotube Growth

The formation of active component of Fe–Mo and Co–Mo catalysts for carbon nanotube growth with variable Mo content is studied with in situ XRD, XPS, and STEM&EDX. The activation of bimetallic Fe–Mo catalysts under the growth conditions leads to the formation of Fe–Mo alloy particles in contrast to Co‐containing catalysts in which active alloy incorporates only a small portion of Mo (<2–3 at.%). The stable carbide formation for these systems is not detected. The effect of Mo content in Fe–Mo and Co–Mo catalysts on the properties of MWCNTs is additionally investigated using the Raman spectroscopy in combination with measurements of the temperature dependence of conductivity. It is shown that MWCNT defectiveness depends on the active component composition for both Fe–Mo and Co–Mo catalysts. The current carrier concentration for the MWCNTs grown on Fe–Mo catalysts slightly increases with the Mo content. The opposite effect is observed for the tubes grown on Co–Mo catalysts, showing a decrease in the current carrier concentration with the increase of Mo concentration.

Microchannel reactor for intensifying oxidation of methanol to formaldehyde over Fe-Mo catalyst

Abstract The paper deals with catalytic oxidation of methanol to formaldehyde in a microchannel reactor (MCR) in view of the process intensification. Every channel in the experimental MCR was 1 mm in diameter, 10 mm in height and was filled with an industrial Fe-Mo catalyst ground to a fraction of 0.15–0.25 mm. Methanol concentration in the feed mixture was 6.5 and 12 mol%, oxygen to methanol molar ratio was 1.5, the temperature was in the range 240–360 °C. Safe processing of the reaction in MCR at methanol concentration as high as 12 mol% makes it possible to reach approximately a 10-fold increase in the specific formaldehyde productivity per unit volume of the catalyst even within the explosive range of oxygen-methanol mixtures. Numerical simulation of the process by use of a continuum model revealed its sufficient consistency with the experimental results. It was shown that methanol conversion decreased by ∼12% after operation for 100 h at 300 °C and 12 mol% of methanol. In contrast, at the same conditions but at standard 6.5 mol% of methanol, the decrease in the conversion did not exceed 3%. The use of MCR for highly exothermic reactions has high potential due to extremely high rates of heat and mass transfer, provided that the catalyst used has stable activity of fine particles during on-stream operation.

Oxidation of methanol to formaldehyde in microchannel reactors: prospects and limitations

Some features of the behavior of highly exothermic selective oxidation processes in a monolith microchannel reactor (MCR) are studied experimentally using the oxidation of methanol to formaldehyde on a Fe–Mo catalyst as an example. The process can be intensified considerably by intensively withdrawing heat from the reaction zone, operating at increased methanol concentrations of up to 12–12.5%, and using catalyst particles smaller than 0.25 mm to increase the useful product yield per unit of catalyst volume by 7–12 times, compared to multitubular reactors. The thermal operating mode of MCRs is close to the optimum theoretical regime for this class of processes, thereby making it easier to achieve high selectivity to formaldehyde. Due to the abovementioned reduction in the activity of Fe–Mo catalyst in MCRs, the prospects for using MCRs in this process must be estimated along with solving the problem of catalyst stability. The use of MCRs appears to be very promising and technologically sound when dealing with catalytic processes whose intensification is not accompanied by an appreciable reduction in activity.

Oxidation of Methanol to Formaldehyde in Microchannel Reactors: Prospects and Limitations

Experimental studies of specific features of high-exothermic selective oxidation in a monolith microchannel reactor (MCR) were carried out with oxidation of methanol to formaldehyde over a Fe-Mo catalyst as an example. The intensive heat withdrawal from the reaction zone, a higher concentration of methanol (up to 12–12,5 %), fine catalyst particles (less than 0,25 mm in size) make it possible to intensify considerably the process and to increase the yield of the target product per catalyst unit volume to as large as 7–12 times of that in tube reactors. The temperature conditions in MCR are close to the theoretically optimal regime for this process family and provide a high selectivity to formaldehyde. While the activity of the Fe-Mo catalyst decreases in MCR, the problem of the catalyst stability should be solved in estimating potentials of MCR in this process. If catalytic processes in MCR can be intensified without noticeable decrease in the catalyst activity, the application of MCR will be rather promising and technologically useful.

Effect of preparation conditions on the composition, structure, and properties of iron–molybdenum catalyst

X-ray phase analysis, synchronous thermal analysis, and IR spectroscopy were used to study the process in which an iron-molybdenum catalyst for partial oxidation of methanol to formaldehyde is prepared. The influence exerted by the pH of the medium on the composition, structure, and properties of the oxide Fe–Mo catalyst was examined. It was found that the amount of the active component in a sample obtained at pH 2 is the largest, and the sample exhibits the best activity in the reaction of methanol oxidation to formaldehyde. The possibility was examined of the occurrence of side reactions in which carbon monoxide is converted. It was found that the conversion occurs only on samples obtained at pH > 2.

Fe-Mo alloy coatings as cathodes in chlorate production process

The aim of this study was to gain a better understanding of the feasibility of partial replacement of dichromate, Cr(VI), with phosphate buffer, focusing on the cathode reaction selectivity for hydrogen evolution on mild steel and Fe-Mo cathodes in undivided cell for chlorate production. To evaluate the ability of phosphate and Cr(VI) additions to hinder hypochlorite and chlorate reduction, overall current efficiency (CE) measurements in laboratory cell for chlorate production on stationary electrodes were performed. The concentration of hypochlorite was determined by a conventional potentiometric titration method using 0.01 mol dm-3 As2O3 solution as a titrant. The chlorate concentration was determined by excess of 1.0 mol dm-3 As2O3 solution and excess of arsenic oxide was titrated with 0.1 mol dm-3 KBrO3 solution in a strong acidic solution. Cathodic hypochlorite and chlorate reduction were suppressed efficiently by addition of 3 g dm-3 dichromate at both cathodes, except that Fe-Mo cathode exhibited higher catalytic activity for hydrogen evolution reaction (HER). The overvoltage for the HER was around 0.17 V lower on Fe-Mo cathode than on mild steel at the current density of 3 kA m-2. It was found that a dichromate content as low as 0.1 g dm-3 is sufficient for complete suppression of cathodic hypochlorite and chlorate reduction onto Fe-Mo catalyst in phosphate buffering system (3 g dm-3 Na2HPO4 + NaH2PO4). The overall current efficiency was practically the same as in the case of the presence of 3 g dm-3 dichromate buffer (98 %). However, for the mild steel cathode, the overall current efficiency for the chlorate production was somewhat lower in the above mentioned mixed phosphate + dichromate buffering system (95%) than in the pure dichromate buffering solution (97.5%).

Optimization of growth temperature of multi-walled carbon nanotubes fabricated by chemical vapour deposition and their application for arsenic removal

Abstract Multi-walled carbon nanotubes have been synthesized at different temperatures ranging from 550 °C to 750 °C on silica supported Fe-Mo catalyst by chemical vapour deposition technique using Cymbopogen flexuous oil under nitrogen atmosphere. The as-grown MWNTs were characterized by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction analysis (XRD) and Raman spectral studies. The HRTEM and Raman spectroscopic studies confirmed the evolution of MWNTs with the outer diameter between 20 and 40 nm. The possibility of using as-grown MWNTs as an adsorbent for removal of As (V) ions from drinking water was studied. Adsorption isotherm data were interpreted by the Langmuir and Freundlich equations. Kinetic data were studied using Elovich, pseudo-first order and pseudo-second order equations in order to elucidate the reaction mechanism.