Fe Catalyst Research Articles

Highly active manganese nitride-europium nitride catalyst for ammonia synthesis

The development of efficient catalysts for ammonia synthesis under mild conditions is critical for establishing a carbon-neutral society powered by renewable ammonia. While significant effort has been focused on Fe and Ru-based catalysts, there have been very limited studies on manganese-based catalysts for ammonia synthesis because of their low intrinsic catalytic activity. Herein, we report that the synergy between manganese nitride (Mn4N) and europium nitride (EuN) yields an ammonia synthesis rate that is 41 and 25 times higher than that of neat Mn4N and EuN, respectively. Detailed studies suggest that a [Eu-N-Mn] species at the interface of Mn4N and EuN plays a pivotal role in ammonia synthesis. Compositing of Mn4N with other rare earth metal nitrides such as LaN, PrN, and CeN also leads to a significant enhancement in catalytic activity. This work broadens the scope of advanced nitride catalysts for ammonia synthesis.

Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.

Further research of the mechanism of char catalytic hydrogasification: Effect of spillover hydrogen on Fe-group catalysts

The mechanism of catalytic hydrogasification of coal remains unclear. This article aims to gain a deeper understanding of the mechanism by examining the effect of spillover hydrogen (SH) on the catalytic hydrogasification activity of Fe-group metals. The SH from CoCa/Al2O3 and CoCa/SiO2 was performed in a fixed bed reactor to enhance the char catalytic hydrogasification. Experimental results revealed that SH enhanced the CH4 yield of all samples. The presence of SH exerted a distinct effect on Fe group metals catalyzed hydrogasification, significantly improved performance for Fe catalyst, relatively minor effect for Ni catalyst, and negligible improvement for Co catalyst. DFT calculation results demonstrated that different metals show distinct abilities on C-C breakage and hydrogen dissociation, which leads to different rate control steps for various metal catalysts in the catalytic hydrogasification. The rate control steps of catalytic hydrogenation by iron group metals are analyzed, and the results agree with the DFT calculation and experimental results.

IFN-γ and IL-10 Immunosensor with Vertically Aligned Carbon Nanotube Interdigitated Electrodes toward Pen-Side Cattle Paratuberculosis Monitoring.

Highly sensitive vertically aligned carbon nanotube arrays (VANTAs) interdigitated electrode (IDE) arrays are developed for electrochemical biosensing of two cytokines (i.e., interleukin-10 (IL-10) and interferon-gamma (IFN-γ)) that are useful for early detection Johne's disease (Bovine Paratuberculosis) in cattle. The high aspect ratio VANTA-IDEs (50-60µm in height) are grown through a chemical vapor deposition process from an iron (Fe) catalyst that is lithographically patterned on a silicon wafer with equal finger width and inter-finger spacing of 25µm. After functionalization with distinct antibodies the VANTA-IDEs are capable of selective detection of both IL-10 and IFN-γ within an actual biological matrix (i.e., diluted bovine implant supernatant) over concentration ranges of 0.1 to 30 pgmL-1 (limit of detection - LOD: 0.0911 pgmL-1) and 50-500 pgmL-1 (LOD: 24.17 pgmL-1), respectively with a response time of <35 min. Results demonstrate important initial steps for rapid, pen-side identification of cattle with stage-I Mycobacterium avium subspecies paratuberculosis infection before physical symptoms of Johne's disease are present. Such a rapid pen-side diagnostic test can be used on cattle at an auction or before they are introduced to a herd to ensure the larger population does not become infected with Johne's disease.

Regulating the Water Dissociation on Atomic Iron Sites to Speed Up CO2 Protonation and Achieve pH‐Universal CO2 Electroreduction

AbstractAtomic Fe sites enabled electrochemical carbon dioxide (CO2) reduction (ECO2R) to carbon monoxide (CO) at low overpotentials. However, the narrow potential ranges for selective CO2 conversion on atomic Fe sites hindered the CO production at high current densities. Therefore, unveiling the CO2 electroreduction processes and clarifying the catalytic mechanisms on different atomic Fe sites are important for better design of atomic Fe catalysts toward efficient ECO2R. Herein, the ECO2R processes on single‐atom, dual‐atom, and cluster Fe sites are systematically investigated, and clarify that the balanced water dissociation and CO2 protonation on dual‐atom Fe sites promote the efficient CO production. The dual‐atom Fe catalyst achieves Faradaic efficiencies of CO (FECO) above 92% over a wide potential range of −0.4–−0.9 V versus reversible hydrogen electrode and maintains FECO of 91% after 153‐h electrolysis in H‐type cell. Benefitting from the favorable CO2 protonation for ECO2R on dual‐atom Fe sites, pH‐universal CO2 electroreduction is achieved in alkali‐/acid‐/bicarbonate‐fed membrane electrode assembly electrolyzer, with FECO exceeds 98% in strongly acidic/alkaline and neutral mediums. The work reveals a water dissociation‐promoted CO2 electroreduction on dual‐atom Fe sites and presents a feasible regulation of atomic Fe sites for highly active/selective ECO2R.

Cu-Fe bimetallic MOFs with long lifetime separated-state charge for enhancing selectivity for CO2 photoreduction to CH4

Improving the CO2 to CH4 conversion efficiency of Cu metal-organic frameworks (Cu-MOFs) catalysts is important for promoting carbon capture and utilization. In this work, a series of novel Cu-Fe bimetallic MOFs photocatalysts (Cu-BTB-Fe with 0.5 wt%, 1.0 wt%, 2.0 wt%, and 4.0 wt% of Fe; H3BTB = 1,3,5-tris(4-carboxyphenyl) benzene) were synthesized by a bimetallic site (Cu and Fe) design strategy in order to improve the electron-hole separation efficiency and CO2 adsorption activation. Findings indicated that the as-synthesized Cu-BTB-2 wt% Fe catalyst exhibited excellent catalytic performance for the conversion of CO2 to CH4 and CO under simulated sunlight irradiation, providing a yield of 32.20 μmol∙g−1∙h−1 and a selectivity of 69.24 % for CO2 to CH4 conversion as well as a yield of 14.29 μmol∙g−1∙h−1 for CO2 to CO conversion without liquid phase products. This is because the Cu-Fe bimetallic sites can continuously supply photoinduced electrons with long separated-state decay lifetime to efficiently activate CO2. Specifically, the Cu-BTB-Fe catalysts provided a high proportion of effective photoinduced electrons with long decay lifetime for the CO* hydrogenation process through a unique electron transfer mechanism, while the strong affinity between CO2 and [Cu2(COO)4]-Fe active units enabled high CO2 adsorption activation and rapid CO2 reduction. The present approach, hopefully, would help to establish feasible pathway for the development of novel highly selective Cu-based MOFs photocatalysts for CO2 photocatalytic reduction yielding CH4.

Exploring Fe Retention in Oxygen Evolution Reaction Catalysts Via Composition Engineering

The oxygen evolution reaction (OER) is an electrochemical half-reaction critical to electrolyzer and metal-air battery technologies. It is well established that Ni (oxy)hydroxides are state-of-the-art electrocatalysts for the OER in basic media when Fe impurities are present in these systems. Morphological studies have shown that these catalysts are prone to dramatic nanoscale reconstruction under electrochemical conditions, implying dissolution, migration and redeposition processes of the catalyst’s components. Processes involving the displacement of Fe are especially important to understand, as these impurities, while essential for high activity at the anode, are often associated with cathode fouling. Describing the parameters that govern Fe leaching is thus of interest for the design of materials aimed toward the maintenance of device performance and longevity. To study how the degree of restructuring relates to Fe dissolution and redeposition, we have prepared a series of electrolyte accessible Ni(z)Co(1-z)O(x)H(y) (z = 0, 0.2, 0.4, ...) thin film catalysts, whereby increased amounts of Co limit the material’s dynamic behavior. By introducing tertiary cations with trackable redox features, we map a parameter space of catalyst composition more or less capable of retaining surface active phases. Parallels with Ni-Co + Fe catalysts are then carried out in Fe-free electrolyte to disrupt absorption-desorption equilibria and connect host-structure dynamics to equilibrium concentrations of electrolyte impurities.

A Simple Approach for Modulating the Active Site in Fe-Based Electrocatalysts

Proton Exchange Membrane Fuel Cells (PEMFCs) have garnered attention as a next-generation, environmentally friendly energy solution to address issues like the climate crisis and depletion of fossil fuels resulting from excessive usage. Nevertheless, the commercialization of PEMFCs faces challenges due to the use of expensive platinum catalysts for the Oxygen Reduction Reaction (ORR). In contrast, Anion Exchange Membrane Fuel Cells (AEMFCs) offer advantages by utilizing cost-effective non-platinum catalysts, making ongoing research on non-platinum catalysts for AEMFCs essential. Numerous studies have been conducted to develop M-N-C catalysts in nanoparticle units using transition metals such as Fe, Co, and Ni for AEMFCs. Notably, Fe-based catalysts with FeNx active sites are considered representative candidates for AEMFCs. Moreover, recent research aims to advance Fe catalysts by incorporating single-atom active sites to enhance mass transfer and improve reaction efficiency at the atomic level.We have developed a straightforward method for synthesizing an Fe catalyst. The catalyst, synthesized through a redox reaction between aniline and a metal ion, followed by pyrolysis, exhibited remarkable durability and activity for the Oxygen Reduction Reaction (ORR). Notably, it possesses an active FeNx site crucial for ORR. Furthermore, by simply altering the solvent during the synthesis process, we observed a variation in the Fe-to-N ratio. Particularly noteworthy was the synthesis of Fe4N, which demonstrated activity for the Oxygen Evolution Reaction (OER). This synthesis method allows for the controlled manipulation of the catalyst's chemistry by varying the solvent, resulting in the production of Fe-based catalysts with either FeNx or Fe4N active sites, active for ORR and OER, respectively. To understand the catalyst's characteristics based on the solvent used during synthesis, we conducted a comprehensive characterization using techniques such as Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The electrochemical activity was investigated through a half-cell test, and efforts were made to interpret the results based on the catalyst's properties.

Theoretical-experimental study of Fe–ZrO2 and Co–ZrO2. Oxidative degradation of methyl orange azo dye

In recent years, advanced oxidation processes (AOPs) based on the generation of sulfate radicals (SO4●-) (SR-AOPs) have emerged as an innovative method for the decontamination of water and wastewater. In this study, Fe(II) and Co(II) catalysts supported on ZrO₂ were synthesized and employed as an activator for PMS and PS for the degradation of methyl orange. The general objective is to gain detailed insight into the interaction between oxidants and supported metal catalysts at the molecular level. Experimental results and density functional theory (DFT) calculations were employed to analyze the potential activation mechanism of the oxidants. The support was prepared via coprecipitation, and metal ion deposition was achieved through incipient wetness impregnation. The characterization of the catalysts was conducted through atomic absorption spectrometry, X-ray diffraction and Fourier-transform infrared spectroscopy. The findings indicated that PMS was the most efficient oxidant, with Co–ZrO2 emerging as the most effective catalyst (77% MO mineralization), compared to Fe–ZrO2, which exhibited a lower degree of mineralization (37.6%) under the specified experimental conditions. The use of PS as an oxidant resulted in low levels of degradation for both catalysts. The remarkable catalytic efficacy of the Co–ZrO₂/PMS system was elucidated through the application of density functional theory (DFT) calculations. These revealed that the adsorption energy of the oxidants on Co–ZrO₂ is lower than that on Fe–ZrO₂, which could facilitate the subsequent release of radicals to the reaction medium.

Controlled growth of single-walled carbon nanotubes with narrow diameter distribution and high areal density on Mn-doped ZrO2-supported Fe catalyst

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution and high areal density hold great promise for a variety of applications, particularly in advanced electronics and biomedical devices. This study utilizes Mn ion doping as a strategic approach both to stabilize the ZrO2-supported Fe catalyst and regulate lattice oxygen release, thereby facilitating the growth of SWCNTs with high areal density and a narrow diameter distribution. The ZrO2-supported Fe catalyst was meticulously dispersed on Si/SiO2 (300 nm) substrates through the optimization of spin-coating speed and solvent viscosity, aiming to enhance the dispersion and uniformity. Investigation into the precise control over the Mn ion content was conducted to regulate the structure and stability of the Mn-doped ZrO2-supported Fe catalyst. Mn ions perform a dual role: they maintain a higher proportion of ZrO2 in the monoclinic phase, which in turn alleviates the monoclinic-tetragonal phase transition during chemical vapor deposition (CVD) growth. Concurrently, the conversion of Mn3+ to Mn4+ ions captures the lattice oxygen released during the formation of zirconium transition oxides. Additionally, first-principles simulations have confirmed the stabilizing impact of Mn ions on the catalyst, which reduces aggregation and maturation, ultimately resulting in a more concentrated diameter distribution of as-grown SWCNTs. This approach has successfully achieved the controlled growth of high areal density SWCNTs with a diameter distribution of 1.73 ± 0.08 nm.

A General Strategy Based on Hetero-Charge Coupling Effect for Constructing Single-Atom Sites.

Single-atom catalysts have emerged as cutting-edge hotspots in the field of material science owing to their excellent catalytic performance brought about by well-defined metal single-atom sites (M SASs). However, huge challenges still lie in achieving the rational design and precise synthesis of M SASs. Herein, we report a novel synthesis strategy based on the hetero-charge coupling effect (HCCE) to prepare M SASs loaded on N and S co-doped porous carbon (M1/NSC). The proposed strategy was widely applied to prepare 17 types of M1/NSC composed of single or multi-metal with the integrated regulation of the coordination environment and electronic structure, exhibiting good universality and flexible adjustability. Furthermore, this strategy provided a low-cost method of efficiently synthesizing M1/NSC with high yields, that can produce more than 50 g catalyst at one time, which is key to large-scale production. Among various as-prepared unary M1/NSC (M can be Fe, Co, Ni, V, Cr, Mn, Mo, Pd, W, Re, Ir, Pt, or Bi) catalysts, Fe1/NSC delivered excellent performance for electrocatalytic nitrate reduction to NH3 with high NH3 Faradaic efficiency of 86.6 % and high NH3 yield rate of 1.50 mg h-1 mgcat. -1 at -0.6 V vs. RHE. Even using Fe1/NSC as a cathode in a Zn-nitrate battery, it exhibited a high open circuit voltage of 1.756 V and high energy density of 4.42 mW cm-2 with good cycling stability.

Single atom catalyst induced by redox reaction between iron ion and aniline monomer

The effective design of a low-cost, efficient, and stable non-noble metal electrocatalyst to substitute the noble metal electrocatalyst for oxygen reduction reaction is highly significant. Even though atomically dispersed metal catalyst shows excellent catalytic activity with maximized atom efficiency, the challenge often lies in achieving uniform distribution for single-atom catalysts owing to their tendency to aggregate. In this work, we present a sequential method that involves the reduction of iron (Fe) mediated by aniline (anchored on support), followed by pyrolysis to fabricate the Fe-Nx moieties and achieve the high density of single atom active sites. The resulting Fe SA 900 catalyst exhibited a half-wave potential of 0.84 V vs. reversible hydrogen electrode (RHE) for oxygen reduction reaction and outstanding stability in alkaline condition. Using various analysis techniques and electrochemical analysis, we demonstrated that the electrocatalytic activity of the catalyst arises from Fe single atom. To validate the practical applicability of Fe-N-C catalysts, we conducted an anion exchange membrane fuel cell (AEMFC) test, which demonstrated a high performance of 212 mW cm−2 at maximum power density. This study proves that the effectiveness of a sequential strategy adopting redox reaction and following pyrolysis for precise synthesis of a single atom Fe catalyst.

Degradation of bromothymol blue and methyl green from aqueous media by Photo-Fenton: comparison between UV-lamp and sun irradiation

Abstract The degradation of two textile dye molecules was studied using photochemical processes, both in the absence and presence of light. Various methods were employed, including photolysis/UV, combined H2O2/UV photolysis, Fe2+/UV treatment, Photo-Fenton/UV at 350 nm and Photo-Fenton with solar irradiation. The decolorization efficiency of dyes in aqueous solution was evaluated for two specific dyes: Bromothymol Blue (BTB) and Methyl Green (MG). These experiments were carried out in batch mode. The results demonstrated a synergy between light irradiation and the presence of Fenton’s reagents, such as hydrogen peroxide and divalent iron. In addition, it was demonstrated that direct solar irradiation can be used without specific devices to achieve high efficiency at low cost. In the first part, we checked the impact of the various operating parameters. Reaction efficiencies were compared for the same system in the dark and under the assistance of an artificial or solar light source. In the second part, we studied the parameters of the Photo-Fenton process, such as the initial pH of the solution, the initial concentrations of oxidant, iron catalyst, and dye under irradiation from either light source. Whereas the mere photolysis without Fenton’s reagents allowed decolorization yields below 26 %, addition of the oxidant (H2O2) or the catalyst (Fe(II) species amplified the treatment efficiency. However, the presence of both H2O2 and Fe(II) under light irradiation was shown synergetic with yields ranging from 72 to 85 % depending on the dye worked and the light source: because of its broader spectrum in the UV domain, solar irradiation led to the highest decolorization yields. The above results were obtained for well-defined proportions of dye and reagents: for a 20 mg/l dye solution, Fe(II) catalyst concentration equal to 10−3 M, peroxide concentration of 5.10−2 M and a pH of 3. These conditions allowed optimal production of OH· radicals, allowing high efficiency in systems using solar irradiation.

Acetylene and Ethylene Adsorption during Floating Fe Catalyst Formation at the Onset of Carbon Nanotube Growth and the Effect of Sulfur Poisoning: a DFT Study.

Here, we investigated the adsorption of acetylene and ethylene on iron clusters and nanoparticles, which is a crucial aspect in the nascent phase of carbon nanotube growth by floating catalyst chemical vapor deposition (FCCVD). The effect of sulfur on adsorption was also studied due to its indispensable role in the process and its commonly known impact on metal catalyst poisoning. We performed systematic density functional theory (DFT) computations, considering numerous adsorption configurations and iron particles of various sizes (Fen, n = 3-10, 13, 55). We found that acetylene binds significantly more strongly than ethylene and prefers different adsorption sites. The presence of sulfur decreased the adsorption strength only in the immediate proximity of the adsorbate, suggesting that the effect of sulfur is mainly of steric origin while electronic effects play only a minor role. Higher sulfur coverage of the catalyst surface significantly weakened the binding of acetylene or ethylene. To further investigate this interaction, Bader's atoms in molecules (AIM) analysis and charge density difference (CDD) were used, which showed electron transfer from iron clusters or nanoparticles to the adsorbate molecules. The charge transfer exhibited a decreasing trend as sulfur coverage increased. These results can also contribute to the understanding of other iron-based catalytic processes involving hydrocarbons and sulfur, such as the Fischer-Tropsch synthesis.

Oxidation of Ammonia Catalyzed by a Molecular Iron Complex: Translating Chemical Catalysis to Mediated Electrocatalysis.

Ammonia is a promising candidate in the quest for sustainable, clean energy. With its capacity to serve as an energy carrier, the oxidation of ammonia opens avenues for carbon-neutral approaches to address worldwide growing energy needs. We report the catalytic chemical oxidation of ammonia by an Earth-abundant transition metal complex, trans-[LFeII(MeCN)2][PF6]2, where L is a macrocyclic ligand bearing four N-heterocyclic carbene (NHC) donors. Using triarylaminium radical cations in MeCN, up to 182 turnovers of N2 per Fe were obtained from chemical catalysis with an extremely low loading of the Fe catalyst (0.043 mM, 0.004 mol % catalyst). This chemical catalysis was successfully transitioned to mediated electrocatalysis for the oxidation of ammonia. Molecular electrocatalysis by the Fe catalyst and the mediator (p-MeOC6H4)3N exhibited a catalytic half-wave potential (Ecat/2) of 0.18 V vs [Cp2Fe]+/0 in MeCN, and achieved 9.3 turnovers of N2 at an applied potential of 0.20 V vs [Cp2Fe]+/0 at -20 °C in controlled-potential electrolysis, with a Faradaic efficiency of 75 %. Based on computational results, the catalyst undergoes sequential oxidation and deprotonation steps to form [LFeIV(NH2)2]2+, and thereafter bimetallic coupling to form an N-N bond.

Oxidation of Ammonia Catalyzed by a Molecular Iron Complex: Translating Chemical Catalysis to Mediated Electrocatalysis

Ammonia is a promising candidate in the quest for sustainable, clean energy. With its capacity to serve as an energy carrier, the oxidation of ammonia opens avenues for carbon‐neutral approaches to address worldwide growing energy needs. We report the catalytic chemical oxidation of ammonia by an Earth‐abundant transition metal complex, trans‐[LFeII(MeCN)2][PF6]2, where L is a macrocyclic ligand bearing four N‐heterocyclic carbene (NHC) donors. Using triarylaminium radical cations in MeCN, up to 182 turnovers of N2 per Fe were obtained from chemical catalysis with an extremely low loading of the Fe catalyst (0.043 mM, 0.004 mol % catalyst). This chemical catalysis was successfully transitioned to mediated electrocatalysis for the oxidation of ammonia. Molecular electrocatalysis by the Fe catalyst and the mediator (p‐MeOC6H4)3N exhibited a catalytic half‐wave potential (Ecat/2) of 0.18 V vs [Cp2Fe]+/0 in MeCN, and achieved 9.3 turnovers of N2 at an applied potential of 0.20 V vs [Cp2Fe]+/0 at −20 °C in controlled‐potential electrolysis, with a Faradaic efficiency of 75%. Based on computational results, the catalyst undergoes sequential oxidation and deprotonation steps to form [LFeIV(NH2)2]2+, and thereafter bimetallic coupling to form an N−N bond.

Nanoparticles of MnFeNiCuBi high entropy alloy as catalyst for Fenton and photo-Fenton decomposition of p-nitrophenol

We report here preparation of an equi-atomic high entropy alloy (HEA) where Bi (hexagonal) was used along with Mn, Fe, Ni and Cu. The HEA assumed fcc structure after ball milling for 60 h of the arc melted component which was initially having multiple phases. XRD and TEM studies corroborated the HEA formation. The XPS studies of the milled sample inferred a probable formation of multicomponent oxide shells on the surface, which could generate a band gap of 1.62 eV. Hence, the present material emerged as an efficient catalyst, which could completely decompose, PNP in 60 min for Fenton and 20 min for photo-Fenton processes. When tested for four cycles, the HEA also displayed appreciable stability as a photo-Fenton catalyst. Further, the catalyst’s soft ferromagnetic nature (MS = 4.55 emu/g) contributes to its recyclability. Given the associated challenges with conventional Fe catalysts utilized in Fenton and photo-Fenton processes, this work provides an alternative as a promising catalyst for treating PNP-containing wastewater.

Performance of V–Fe based catalysts on the oxidation of dibenzothiophenes

To obtain fossil fuels with ultra-low S levels at friendly conditions, different V oxides formulations on alumina modified with Fe were characterized and selected to oxidize dibenzothiophene (DBT), 4-methyl DBT and 4,6-dimethyl DBT prevailing in diesel fuel. V–Fe based catalysts (5 or 10 wt% of V) were obtained by impregnation of ammonium metavanadate solutions on Fe-modified alumina, obtained by impregnation of Mohr salt on pseudoboehmite (2 wt% of Fe). The catalysts were calcined in air atmosphere, and after were partially reduced with H2 flux to obtain a mix of several oxidation states of V and Fe species, to evaluate the interaction of Fe in VOx/Al2O3 catalysts and determine its effect on the oxidation processes. The structural and optical properties, as well as surface species, were determined by SEM-EDS, TPR, XRD, Raman, ATR-FTIR, photoluminescence, UV–Vis diffuse reflectance, and XPS spectroscopy. The catalytic performance was evaluated in oxidative desulfurization (ODS) and photocatalytic ODS (PODS) processes. The experimental results showed the addition of Fe promoted the catalytic activity of both ODS and PODS reactions. ODS activities of V–Fe catalysts increase up to 7.5 times with respect to V catalysts without Fe, and the most active catalyst (V5Fer) presents a characteristic oxidation time of 50 min for 4,6-DMDBT. The PODS activity of V10Fec was like ODS activity, showing it is possible to oxidize the dibenzothiophenes under friendly conditions to obtain lower S levels. The promoting effect of Fe was due to the interaction of Fe2+ and Fe3+ with the catalytic support, favoring the distribution of surface V3+ and V4+ species. Additionally, Fe improved the optical properties of the catalysts since the bandgap energy decrease and low recombination rate of the electron-hole pair were observed. Therefore, V–Fe based catalysts are photocatalytically actives to be used in PODS processes.

Kinetic modelling of non-equilibrium plasma enhanced catalytic ammonia decomposition

It is important for the usage of ammonia as energy carrier to achieve ammonia decomposition at low temperature. In the present study, a reactor model of plasma catalytic ammonia decomposition over Fe catalyst at atmospheric pressure is developed in the aspect of plasma and chemical synergies kinetics. The plasma catalytic model accounted for multiple physical mechanisms in electronic and vibrational plasma kinetics and detailed ammonia decomposition mechanisms on the catalyst surface. In addition, a novel view that identify the surface chemisorption enhancement by plasma attributed to charge transfer via EMSI (electronic metal-support interaction) effect is highlighted. The result shows that the synergetic effect of plasma and thermal-catalyst is much greater than that of plasma or catalyst alone on ammonia decomposition, especially at low temperature. It is revealed that the surface desorption of nitrogen is still the rate-limiting step. Moreover, the numerical results also indicate that Langmuir-Hinshelwood reaction via 2 N(s)=>N2 is more likely to dominate the surface desorption of nitrogen in the presence of plasma rather than Eley-Rideal reaction via N + N(s)=>N2. At low electric field, there are infrequent free radicals (NH2, NH and N) and few vibrational ammonia (NH3(v)) generated by the plasma, thus considering that the adsorbed ammonia only undergoes a three-step dehydrogenation reaction. As a consequence, the rate of surface nitrogen desorption with plasma is greater than that with catalyst alone since plasma promotes the chemisorption process of ammonia. This work provides new fundamental insights into the synergistic effect of plasma and catalyst, as well as the direction for the ammonia decomposition catalyst design in plasma.

Enhancing catalyst stability: Immobilization of Cu–Fe catalyst in sodium alginate matrix for methyl orange removal via Fenton-like reaction

This study aims to enhance the stability and effectiveness of heterogeneous catalysts in Fenton-like reactions, explicitly addressing the acidity limitations inherent in traditional Fenton processes. Copper-iron was synthesized through co-precipitation, and a catalyst bead was produced from hydrogel formation. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirm phases in the bimetallic Copper-iron, aligning with the intended composition. Modification with alginate led to reduced metal leaching compared to the bare bimetallic counterpart, as confirmed by atomic absorption spectroscopy (AAS). Additionally, Fourier-transform infrared spectroscopy (FTIR) revealed the deactivation of alginate through the disappearance of carboxyl groups, indicating the depolymerization of the catalyst bead. Under the suggested conditions (Methyl Orange concentration of 25 mg/L, initial solution pH of 7, 2 g/L catalyst loading, concentration of hydrogen peroxide 100 mM in a 120-min reaction time), the catalyst demonstrated remarkable decolorization efficiency of Methyl Orange, achieving 97.67 %. Further highlighting its practicality, the catalyst exhibited outstanding reusability over four cycles under identical conditions, showcasing robust immobilization capabilities and sustained performance. Notably, the catalyst's magnetic properties facilitated easy separation using an external magnet. In conclusion, the developed catalyst beads offer a solution with high reusability, magnetic separability, and reduced iron leaching. The advantageous characteristics underscore its potential as a heterogeneous catalyst for wastewater treatment applications, warranting further exploration under practical conditions.