Search Results (202)

Nickel–iron (Ni-Fe) catalysts are widely used in industry due to their cost-effectiveness and versatile catalytic properties. This work investigates the structural and morphological characteristics of Ni-Fe catalysts supported on γ-Al₂O₃, synthesized with varying Ni/Fe atomic ratios (from 1:1 to 20:1). The catalysts were characterized using a combination of experimental techniques including X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), and selected-area electron diffraction (SAED). Theoretical modeling using the USPEX evolutionary algorithm complemented the experimental data by predicting stable Ni-Fe crystal structures. The results revealed uniform metal distribution on the support with particle sizes ranging from 4.1 to 4.5 nm. SAED analysis confirmed the formation of an intermetallic FeNi phase, particularly in samples with higher iron content. This study demonstrates Ni-Fe interaction effects and will be of interest to researchers in catalysis and materials science working on the development of bimetallic systems. Full article

Developing efficient and recyclable periodate (PI)-based advanced oxidation processes (AOPs) for the removal of emerging organic pollutants (EOPs) has attracted considerable attention. However, the structure–activity relationship of single-atom catalyst in PI-AOP systems remains poorly understood. In this study, a hollow carbon-supported single-Fe atom catalyst (HCFe800) was synthesized and applied for PI activation toward bisphenol A (BPA) degradation. Under neutral pH and ambient temperature, HCFe800 enabled complete removal of BPA within 1 min, achieving a degradation rate constant (k) of 5.094 min⁻¹—approximately 3 and 10 times higher than that of Fe-free and solid control catalysts, respectively. After normalization, the apparent degradation rate constant was 1–3 orders of magnitude greater than those of previously reported catalysts. The optimized Fe doping amount and pyrolysis temperature facilitated the formation of atomically dispersed FeN₄ sites, which outperformed Fe clusters and iron oxides in catalytic activity. The hollow porous structure further enhanced the exposure of active sites, contributing to the exceptional performance. The HCFe800/PI system remained highly effective across broad pH (3–7) and temperature (5–35 °C) ranges and in the presence of 100-fold concentrations of common inorganic ions. Mechanistic studies revealed that the main reactive species were ¹O₂, O₂^•−, and IO₃^•, with negligible involvement of high-valent Fe species. Eight less-toxic BPA degradation products were identified. Moreover, the system was extendable to various other EOPs and exhibited excellent recyclability via thermal regeneration. This work provided fundamental insights into designing and applying single-atom catalysts for PI-based advanced treatment of EOPs. Full article

A comprehensive literature review highlights how the nature of active metals, support materials, promoters, and synthesis methods influences catalytic performance, with particular attention to ruthenium-based catalysts as the current benchmark. Kinetic models are presented to describe the reaction pathway and predict catalyst behavior. Various reactor configurations, including fixed-bed, membrane, catalytic membrane, perovskite-based, and microreactors, are evaluated in terms of their suitability for ammonia decomposition. While ruthenium remains the benchmark catalyst, alternative transition metals such as iron, nickel, and cobalt have also been investigated, although they typically require higher operating temperatures (≥500 °C) to achieve comparable conversion levels. At the industrial scale, catalyst development must balance performance with cost. Inexpensive and scalable materials (e.g., MgO, Al₂O₃, CaO, K, Na) and simple preparation techniques (e.g., wet impregnation, incipient wetness) may offer lower performance than more advanced systems but are often favored for practical implementation. From a reactor engineering standpoint, membrane reactors emerge as the most promising technology for combining catalytic reaction and product separation in a single unit operation. This review provides a critical overview of current advances in ammonia decomposition for hydrogen production, offering insights into both catalytic materials and reactor design strategies for sustainable energy applications. Full article

Steel pickling sludge serves as a valuable iron source for synthesizing Fe-based catalysts in heterogeneous advanced oxidation processes (AOPs). Here, MoS₂@CoFe₂O₄ catalyst derived from steel pickling sludge was prepared via a facile solvothermal approach and utilized to activate peroxymonosulfate (PMS) for tetracycline hydrochloride (TCH) degradation. Comprehensive characterization using scanning electron microscopy (SEM)-energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) confirmed the supported microstructure, composition, and crystalline structure of the catalyst. Key operational parameters—including catalyst dosage, PMS concentration, and initial solution pH—were systematically optimized, achieving 81% degradation efficiency within 30 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed SO₄^∙− as the primary oxidative species, while the catalyst maintained high stability and reusability across cycles. TCH degradation primarily occurs through hydroxylation, decarbonylation, ring-opening, and oxidation reactions. This study presents a cost-effective strategy for transforming steel pickling sludge into a high-performance Fe-based catalyst, demonstrating its potential for practical AOP applications. Full article

The biomass-to-liquid process is a promising alternative for sustainably meeting the growing demand for liquid fuels. This study focuses on the fabrication, characterization, and performance of a structured iron catalyst for producing hydrocarbons through Fischer–Tropsch synthesis (FTS). The catalyst was designed to address some drawbacks of conventional supported catalysts, such as low utilization, poor activity, and instability. The experimental investigation involved the manufacturing and characterization of both promoted and unpromoted iron-based catalysts. The performance of the structured iron catalyst was assessed in a fixed-bed reactor under relevant industrial conditions. Notably, the best results were achieved with a syngas ratio typical of the gasification of lignocellulosic biomass, where the catalyst exhibited superior catalytic activity and selectivity toward desired hydrocarbon products, including light olefins and long-chain paraffins. The resulting structured catalyst achieved up to 95% CO conversion in a single pass with 5% selectivity for CH₄. The results indicate that the developed structured iron catalyst has considerable potential for efficient and sustainable hydrocarbon production via the Fischer–Tropsch synthesis. The catalyst’s performance, enhanced stability, and selectivity present promising opportunities for its application in large-scale hydrocarbon synthesis processes. Full article

This study discloses the noncovalent immobilization of a bienzyme cascade composed of glucose oxidase (GOx) and horseradish peroxidase (HRP) onto magnetically responsive polyamide microparticles (PA MPs). Porous PA6, PA4, and PA12 MPs containing iron fillers were synthesized via activated anionic ring-opening polymerization in suspension, alongside neat PA6 MPs used as a reference. Four hybrid catalytic systems (GOx/HRP@PA) were prepared through sequential adsorption of HRP and GOx onto the various PA MP supports. The initial morphologies of the supports and the hybrid biocatalysts were characterized by SEM, followed by evaluation of the catalytic performance using a two-step glucose oxidation cascade process. Among all systems, the GOx/HRP@PA4-Fe complex exhibited the highest activity, being approximately 1.5 times greater than the native enzyme dyad, followed by the PA6-supported system with slightly inferior performance. All systems obeyed Michaelis–Menten kinetics, with the immobilized cascades displaying higher Kₘ and Vₘₐₓ values than the non-immobilized enzyme pair while maintaining comparable catalytic efficiencies, CE (CE = k_cat/Kₘ). Subsequently, the immobilized and native enzyme systems were employed for the polymerization of aniline. According to UV–VIS, complete monomer conversion was achieved within 24 h for selected catalysts, and FTIR analysis confirmed the formation of polyaniline in the emeraldine base form without the use of template molecules. These findings highlight the potential of Fe-containing polyamide microparticles as efficient supports for the sustainable, enzyme-mediated synthesis of intrinsically conductive aromatic polymers. Full article

Catalytic methane decomposition offers an attractive and sustainable pathway for producing CO_x-free hydrogen and valuable carbon nanotubes. This work investigates the innovative use of liquid metals, particularly gallium and indium, as promoters for iron catalysts based on a titanium dioxide and alumina composite to improve this process even more. In a fixed-bed reactor operating at 800 °C and atmospheric pressure, all catalyst activities for methane decomposition were thoroughly assessed while keeping the gas hourly space velocity at 6 L/g h. Surface area and porosity, H₂-temperature programmed reduction/oxidation, X-ray diffraction, Raman spectroscopy, scanning transmission electron microscopy, and thermogravimetry analysis were utilized to investigate the physicochemical properties of the catalyst. The result showed that iron supported on a titanium-alumina catalyst exhibited higher activity, stability, and reproducibility with a methane conversion of 90% and hydrogen production of 81% after three cycles, with 240 min for each cycle and stability for 480 min. In contrast, the liquid metal-promoted catalysts improved the metal-support interaction and textural properties, such as surface area, pore volume, and particle dispersion of the catalysts. Still, the catalytic efficiency significantly improved. However, the gallium-promoted catalyst displayed excellent reusability. The characterization of the spent catalyst proved that both the iron supported on a titanium-alumina and its gallium-promoted derivative produced graphitic carbon; on the contrary, the indium-promoted catalyst produced amorphous carbon. These results demonstrate how liquid metal promoters can be used to adjust the characteristics of catalysts, providing opportunities for improved reusability and regulated production of carbon byproducts during methane decomposition. Full article

Current biodiesel production is costly, in part due to the catalysts added during transesterification and later washed out. We have previously shown that intact rapeseed shells can be ball-milled with an alcohol to produce biodiesel without an added catalyst. Here, we report on the activation and identity of the complexing agent within the shells of rapeseeds and sunflower seeds. Lignin, present in the cell walls of plant matter, complexes with iron and manganese within metallic media, such as in a ball mill, and acts as a catalyst support in a transesterification reaction with oil and methanol. When ball-milled with methanol, rapeseed and sunflower seeds produce up to 90% biodiesel, similar to yields produced by industrial methods. However, this new method for producing biodiesel is a greener alternative, as it requires fewer organic solvents, may reduce the time and energy required for synthesis, and may reduce the effort required for product purification. Full article

The anodic stability of tungsten carbide (WC) and iron oxide with a spinel structure (Fe₃O₄) were compared against similar data for nanostructured, boron-doped diamond (BDD), and the benchmark Vulcan XC72 carbon, in view of their eventual application as alternative supports for the anion exchange membrane electrolyzer anode. To this end, metal oxide composites were prepared by the in situ autocombustion (ISAC) method, and the anodic behavior of materials (composites as well as supports alone) was investigated in 1 M NaOH electrolyte by the rotating ring–disc electrode method, which enables the separation oxygen evolution reaction and materials’ degradation currents. Among all supports, BDD has proven to be the most stable, while Vulcan XC72 is the least stable under the anodic polarization, with Fe₃O₄ and WC demonstrating intermediate behavior. The Co₃O₄-BDD, -Fe₃O₄, -WC, and -Vulcan composites prepared by the ISAC method were then tested as catalysts of the oxygen evolution reaction. The Co₃O₄-BDD and Co₃O₄-Fe₃O₄ composites appear to be competitive electrocatalysts for the OER in alkaline medium, showing activity comparable to the literature and higher support stability towards oxidation, either in cyclic voltammetry or chronoamperometry stability tests. On the contrary, WC- and Vulcan-based composites are prone to degradation. Full article

Catalytic CO₂ methanation represents a promising process route for converting carbon dioxide into methane, a valuable energy carrier. This study investigates the performance of Ni-based catalysts on mixed silica and MgO support materials for CO₂ methanation. Silica was derived from rice husk (SiO₂(RH)), representing a sustainable, cost-effective source for catalyst support, and MgO was used as a reference and to enhance the catalytic activity of the Ni-based catalysts through admixture with SiO₂(RH). The results were compared to CO₂ methanation over Ni-based catalysts on reduced iron ore from natural siderite (siderite_reduced), providing another abundant source for catalyst support. The experiments were conducted in a tubular reactor with a feed gas composition of H₂:CO₂:N₂ = 56:14:30, feed gas flow rates ranging from 4.01 to 14.66 m³·kg⁻¹·h⁻¹ (STP), and reaction temperatures of 548–648 K. The highest CO₂ conversion with the Ni/SiO₂(RH) catalyst was 39.01% at a methane selectivity of 92.64%. The use of mixed silica and MgO supports (SiO₂(RH)/MgO) for nickel revealed a beneficial effect, enhancing CO₂ conversion and methane formation. In this case, methane selectivities consistently exceeded 91.57%. Superior methane selectivity and CO₂ conversion were obtained with Ni/MgO catalysts and Ni/SiO₂(RH)/MgO catalysts with high MgO fractions, highlighting the fundamental effect of MgO in the catalyst support for CO₂ methanation. Full article

The transition from fossil resources to renewable raw materials derived from lignocellulosic waste is crucial for economic and environmental sustainability. Advancing toward a bio-based economy necessitates the development of innovative heterogeneous catalysts. This study explores the use of modified sugarcane bagasse biochar, embedded with ruthenium and iron particles, as a green catalyst for converting levulinic acid (LA) to γ-valerolactone (GVL). The efficiency of both raw and modified biochar in the LA to GVL conversion process, utilizing formic acid (FA) exclusively as the hydrogen source, was systematically assessed through characterization techniques, including XRD, TGA, XPS, and SEM/EDS. The gelification method using alginate enhanced the ruthenium and iron content on the surface of the biochar. The results demonstrate that the modified material has significant potential for efficient LA-to-GVL conversion, achieving a yield of 73.0 ± 9.2% under optimized conditions (0.5 g of BC₅₀₀Fe/3%Ru at 180 °C for 3 h, with 4 mmol LA, 8 mmol FA, and 10 mL of water). Iron on the biochar surface facilitated the formation of adsorption sites for LA, supporting the notion of this novel catalyst for LA conversion in an aqueous medium in the presence of FA. This research underscores the potential of this green catalyst in advancing sustainable biomass conversion and contributes to the ongoing shift towards a bio-based economy. Full article

Developing high-performance oxygen evolution reaction (OER) electrocatalysts remains a critical challenge for sustainable hydrogen production via water electrolysis. Herein, we present a self-supported atomic iridium-decorated FeOOH nanostructure on iron foam (Ir-FeOOH/IF) by a facile impregnation reduction method. The self-supported Ir-FeOOH/IF electrode integrates the high electrical conductivity and outstanding mass transfer performance of IF. The FeOOH features abundant active sites, while the Ir modification regulated the electronic structure of FeOOH. As a result, the as-prepared Ir-FeOOH/IF catalyst (with the optimized synthesis time) achieves a low overpotential of 145 and 284 mV at current densities of 0.1 and 1 A cm⁻², respectively, and exhibits excellent long-term catalytic stability for 135 h at 0.1 A cm⁻² in a 1 M KOH solution. This work provides a new strategy for the design of low-cost and highly stable OER electrocatalysts. Full article

Carbon monoxide (CO) is an important air pollutant generated from the incomplete combustion of fossil fuels, particularly in industrial processes such as iron and steel smelting, power generation, and waste incineration, posing environmental challenges that demand effective removal strategies. Recent advances in noble metal catalysts for catalytic oxidation of CO, particularly Pt-, Pd-, and Rh-based systems, have been extensively studied. However, there is still a lack of systematic review on noble metal-based catalytic oxidation of CO, especially regarding the effects of different active components of the catalysts and the mechanism of sulfur resistance. Based on extensive research and literature findings, this study comprehensively concluded the advances in noble metal-based catalytic oxidation of CO. The effects of preparation methods, supports, and physicochemical properties on the catalytic performance of CO were explored. In addition, the mechanism of the catalytic oxidation of CO were further summarized. Furthermore, given the prevalence of SO₂ in the flue gas, the mechanism of sulfur poisoning deactivation of catalysts and the anti-sulfur strategies were further reviewed. Exploration of new supporting materials, catalyst surface reconstruction, doping modification, and other catalyst design strategies demonstrate potential in improving sulfur resistance and catalytic efficiency. This study provides valuable insights into the design and optimization of noble metal-based catalysts for the catalytic oxidation of CO. Full article

The development of efficient, sustainable, and cost-effective catalysts is crucial for energy storage technologies, such as zinc–air batteries (ZABs). These batteries require bifunctional catalysts capable of efficiently and selectively catalyzing oxygen redox reactions. However, the high cost and low selectivity of conventional catalysts hinder the large-scale integration of ZABs into the electric grid. This study presents binder-free Fe-based bifunctional electrocatalysts synthesized via a sol–gel method, followed by thermal treatment under ammonia flow. Supported on nickel foam, the catalyst exhibits enhanced activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), essential for ZAB operation. This work addresses two critical challenges in the development of ZABs: first, the replacement of costly cobalt or platinum-group-metal (PGM)-based catalysts with an efficient alternative; second, the achievement of prolonged battery performance under real conditions without passivation. Structural analysis confirms the integration of iron nitrides, oxides, and carbon, resulting in high conductivity and catalytic stability without relying on precious or cobalt-based metals. Electrochemical tests reveal that the catalyst calcined at 800 °C delivers superior performance, achieving a four-electron ORR mechanism and prolonged operational life compared to its 900 °C counterpart. Both catalysts outperform conventional Pt/C-RuO₂ systems in stability and selective bifunctionality, offering a more sustainable and cost-effective alternative. The innovative combination of nitrogen, carbon, and iron compounds overcomes limitations associated with traditional materials, paving the way for scalable, high-performance applications in renewable energy storage. This work underscores the potential of transition metal-based catalysts in advancing the commercial viability of ZABs. Full article

Mössbauer spectroscopy can be advantageous for studying catalysts. In particular, its use in in situ studies can provide unique access to structural features. However, special attention must be paid to the interpretation of data, since in most studies, the samples are not perfectly homogeneous. Balance and compromise should be found between the refinement of evaluations by extracting and interpreting data from spectra, while also considering the presence of possible inhomogeneities in samples. In this review, examples of studies on two types of catalysts are presented, from which, despite possible inhomogeneities, clear statements can be derived. The first example pertains to selected iron-containing microporous zeolites (with ⁵⁷Fe Mössbauer spectroscopy), from which unique information is collected on the coordination of iron ions. The second example is related to studies on supported PtSn alloy particles (with ¹¹⁹Sn probe nuclei), from which reversible modifications of the tin component due to interactions with the reaction partners are revealed. Full article