Alternative Catalyst Research Articles

The Synthesis, Characteristics, and Application of Hierarchical Porous Materials in Carbon Dioxide Reduction Reactions

The reduction of carbon dioxide to valuable chemical products could favor the establishment of a sustainable carbon cycle, which has attracted much attention in recent years. Developing efficient catalysts plays a vital role in the carbon dioxide reduction reaction (CO2RR) process, but with great challenges in achieving a uniform distribution of catalytic active sites and rapid mass transfer properties. Hierarchical porous materials with a porous hierarchy show great promise for application in CO2RRs owing to the high specific surface area and superior porous connection. Plenty of breakthroughs in recent CO2RR studies have been recently achieved regarding hierarchical porous materials, indicating that a summary of hierarchical porous materials for carbon dioxide reduction reactions is highly desired and significant. In this paper, we summarize the recent breakthroughs of hierarchical porous materials in CO2RRs, including classical synthesis methods, advanced characterization technologies, and novel CO2RR strategies. Moreover, by highlighting several significant works, the advantages of hierarchical porous materials for CO2RRs are analyzed and revealed. Additionally, a perspective on hierarchical porous materials for CO2RRs (e.g., challenges, potential catalysts, promising strategies, etc.) for future study is also presented. It can be anticipated that this comprehensive review will provide valuable insights for further developing efficient alternative hierarchical porous catalysts for CO2 reduction reactions.

Combination of Biochar and Advanced Oxidation Processes for the Sustainable Elimination of Pharmaceuticals in Water

The presence of pharmaceuticals in aquatic ecosystems is an issue of increasing concern. Regardless of the low concentration of pharmaceuticals in water, they can have a toxic effect on both humans and aquatic organisms. Advanced oxidation processes (AOPs) have been described as a promising technique for eliminating pharmaceuticals due to their high efficiency. However, the cost associated with the application of these processes and their high reagents and energy requirements have affected the implementation of AOPs at large scales. Biochar has been suggested to be used as a catalyst in AOPs to overcome these limitations. Biochar is considered as an alternative heterogeneous catalyst thanks to its physicochemical characteristics like its specific surface area, porous structure, oxygen-containing functional groups, electrical conductivity, persistent free radicals (PFRs), modifiable properties, and structure defects. This carbonaceous material presents the capacity to activate oxidizing agents leading to the formation of radical species, which are needed to degrade pharmaceuticals. Additionally, AOP/biochar systems can destroy pharmaceutical molecules following a non-radical pathway. To enhance biochar catalytic performance, modifications have been suggested such as iron (Fe) impregnation, heteroatom doping, and supporting semiconductors on the biochar surface. Although biochar has been efficiently used in combination with several AOPs for the mineralization of pharmaceuticals from water, further research must be conducted to evaluate different regeneration techniques to increase biochar’s sustainable applicability and reduce the operational cost of the combined process. Moreover, operational conditions influencing the combined system are required to be evaluated to discern their effect and find conditions that maximize the degradation of pharmaceuticals by AOP/biochar systems.

Sustainable Processes Reusing Potassium-Rich Biomass Ash as a Green Catalyst for Biodiesel Production: A Mini-Review

To mitigate the emissions of greenhouse gases (GHGs) from fossil fuels, the use of biodiesel and its sustainable production have been receiving more attention over the past decade, especially for the reuse of waste cooking oils and non-edible oils as starting feedstocks. For the biodiesel production process, the suitability of a green catalyst is a core function in the transesterification reaction. Heterogeneous (solid-state) catalysts are generally superior to homogeneous (liquid-state) catalysts due to several significant advantages such as no saponification products formed, recyclability, and less equipment corrosion. Recent studies also revealed that heterogeneous solid base catalysts were widely used for the production of biodiesel. Furthermore, the use of biomass-based ash derived from herbaceous and agricultural biomass is increasing rapidly because of its environmental sustainability, high biodiesel yield, and low catalyst cost. To highlight alternative catalysts from biomass residues, this mini-review paper thus focused on a summary of various heterogeneous potassium-rich ash materials, which were used as green catalysts for the sustainable production of biodiesel. Due to the abundant quantity and chemical compositions, it was found that ash derived from cocoa pod husk may be the most commonly used solid base catalyst for producing biodiesel in the literature. Finally, future perspectives on biodiesel production by adopting emerging technologies and using high-potassium (K) biomass ash as a green catalyst were also addressed.

Sustainable synthesis of Di-iso-octyl Maleate using 3-octanol extracted from Peppermint oil

Surfactants are vital in industries such as detergents, textiles, and cosmetics, and their synthesis from renewable or waste-derived feedstocks aligns with sustainability goals. This study explores the valorization of 3-octanol, a byproduct of peppermint oil extraction, into di-isooctyl maleate (DOM), a precursor to di-octyl sulphosuccinate (DOSS), a widely used surfactant. The synthesis of DOM was achieved via esterification of 3-octanol and maleic anhydride in the presence of para-toluene sulphonic acid (PTSA) as a catalyst. Reaction parameters, including catalyst concentration, reaction time, and temperature, were systematically optimized to maximize yield. The highest yield of 96.34% was obtained using 0.4 g of PTSA per 5 g of 3-octanol, with an optimal temperature of 80–85°C and a reaction time of 3 hours. Experimental data showed a decline in yield beyond this catalyst concentration and reaction duration, indicating the importance of precise parameter control. Alternate catalysts such as Amberlite and Indion 130 were tested. This study demonstrates a sustainable and scalable approach to converting waste-derived 3-octanol into value-added surfactants, providing an economically viable solution with minimal equipment and investment requirements.

Magnesium oxide-supported potassium hydride as a transition-metal-free catalyst for the selective hydrogenation of alkynes

Catalytic hydrogenation of alkynes to alkenes is pivotal in both petrochemical and fine chemical industries. Its implementation relies on the use of transition metals, especially those precious Pd-based catalysts. In this work, we utilize a melt infiltration method to prepare magnesium oxide-supported potassium hydride (KH/MgO), which is illustrated as a transition-metal-free catalyst for selective hydrogenation of alkynes. H2-D2 exchange experiment proves that dihydrogen activation and dissociation on KH/MgO is plausible at room temperature and ambient pressure. KH/MgO catalyzes hydrogenation of diphenylacetylene (DPA) already at 40 ℃, implying its high intrinsic activity at very mild conditions. Under an optimized condition of 80°C, 2 bar H2, and 40 h, 75 % conversion of DPA is achieved, affording 82 % selectivity to stilbenes. Mechanistic study suggests that surface hydride on KH/MgO plays an important role toward dihydrogen activation, and involved in the hydrogenation step to form stilbenes. This work shows the promise for using light metal hydrides consisting of earth-abundant elements as alternative hydrogenation catalysts.

Highly Active NiRu/C Cathode Catalyst Synthesized by Displacement Reaction for Anion Exchange Membrane Water Electrolysis.

Anion exchange membrane water electrolysis (AEMWE) is highly promising for cost-effective green hydrogen production due to its basic operating conditions facilitating the use of non-noble catalysts. While non-noble Ni/Fe-based catalysts are utilized at the anode, its cathode catalyst still requires precious Pt. Due to the high cost of Pt and the sluggish hydrogen evolution reaction (HER) at the cathode in basic conditions, developing alternative catalysts to replace Pt is highly important. Here, a synthesis procedure for a Ru-based catalyst is reported and its high activity toward the HER in alkaline media is demonstrated in both half-cell and single-cell tests. The catalyst is synthesized in a two-step approach. A highly dispersed Ni catalyst is prepared on carbon support in the first step. In the second step, Ru is deposited on its surface using a galvanic displacement reaction. The uniqueness of this method is that Ru is deposited over the entire electrically conductive surface, resulting in an isotropic and homogeneous Ru distribution within the catalyst powder. It is demonstrated that this material remarkably outperforms state-of-the-art Pt/C catalysts in half-cell and single-cell tests. The single cell only requires 1.73V at 1A cm-2 with an overall PGM content of 0.05mg cm-2.

Gold Salts as Alternative Catalysts in Promoting Cascade Condensation of 2-Aminobenzaldehydes with Alcohols and Amines.

The distinctive features of gold self-relay catalysts were alternatively utilized in the intriguing cascade condensation of 2-aminobenzaldehydes with alcohols and amines. Using NaAuCl4·2H2O as a catalyst, a range of 13-alkyloxy-7,11b-dihydro-6H,13H-6,12-[1,2]benzenoquinazolino[3,4-a]quinazoline derivatives was produced in good to high yields through A3B condensation of various 2-aminobenzaldehydes with alcohols. By carefully choosing the reaction conditions, gold catalysis also proved effective for A2B condensation with primary aryl- and benzylamines, facilitating the synthesis of challenging McGeachin bisaminals, including a chiral nonracemic derivative of 2-(S)-methylbenzylamine. The mild conditions of this gold-catalyzed approach may lead to new advancements in the field.

Improved photocatalytic degradation of methylene blue by novel hexagonal ZnO particles

Recently, the use of nanoparticles as photocatalysts has gained great importance. However, nanoparticles exhibit some drawbacks for this application and there is a need for new particle technologies to mitigate these drawbacks. A novel particle technology called MicNo based on ZnO has been designed and manufactured, which exhibits the advantages and properties of both micron and nano size. Although performance of MicNo-ZnO has been tested in various applications, it has not been tested as a photocatalyst in any photocatalytic degradation process. In this study, novel designed ZnO was used as a catalyst for methylene blue (MB) degradation in the presence of UV irradiation. The MicNo-ZnO particles were characterized by structural and morphological properties by XRD, BET and SEM analyses. The effects of catalyst amount, pH, temperature and initial concentration on the degradation process were investigated. In addition, a reusability study was carried out with 4 cycles under optimum conditions. The MicNo-ZnO particles showed excellent photocatalytic activity with a degradation rate of 96% for methylene blue in 180 min. The pseudo-first-order rate constant for the photocatalytic degradation of MB by MicNo-ZnO was as high as 0.0236 min−1, confirming that MicNo-ZnO particles can be effectively utilized as an alternative catalyst material.

Corrolato(oxo)antimony(V) Dimer with Hydrogen-Bond Donor Groups in Secondary Coordination Sphere as a Catalyst for Hydrogen Evolution Reaction.

The focus is on developing alternative molecular catalysts using main-group elements and implementing strategic improvements for sustainable hydrogen production. For this purpose, a FB corrole with a (2-(2-((4-methylphenyl)sulfonamido)ethoxy)phenyl) group inserted into the meso position (C-10) of the corrole, along with its high-valent (corrolato)(oxo)antimony(V) dimer, was synthesized. In the crystal structure analysis of the FB corrole and the (corrolato)(oxo)antimony(V) dimer complex, it was noted that the sulfonamido group in the ligand periphery sits atop the corrole ring. The electrochemical hydrogen evolution reaction (HER) of the (corrolato)(oxo)antimony(V) dimer was studied and compared with a previously reported (corrolato)(oxo)antimony(V) complex, which lacks hydrogen-bond donor groups in the secondary coordination sphere. The newly designed molecules, featuring hydrogen-bond donor groups in the secondary coordination sphere, demonstrated clear superiority in the electrochemical HER. Controlled potential electrolysis was employed to evaluate the charge accumulation associated with hydrogen generation in a homogeneous three-electrode system in the presence of 50 mM TFA. The produced hydrogen exhibits a Faradaic efficiency of approximately 80.96%, a turnover frequency (TOF) of 0.44 h-1, and a production rate of 52.83 μL h-1, highlighting the effective catalytic activity of the (corrolato)(oxo)antimony(V) dimer in hydrogen evolution.

Density functional theory studies of Pd and PtxPd1–x bimetallic catalysts for the H2/O2 recombination reaction

Choosing an appropriate H2/O2 recombination catalyst is crucial for enhancing efficiency in hydrogen technologies. This study used density functional theory calculations to investigate PtxPd1–x (0 ≤ x ≤ 1) alloys with varying slab thicknesses and surface areas. The performance of these alloys and the reaction intermediates (O, H, OH, OH + H, H2O) formed on the catalyst surfaces for the H2/O2 recombination reaction was analysed. Catalytic activity of pristine Pd (111) and PtPd3, PtPd, Pt3Pd, and Pt7Pd (111) alloy surfaces was evaluated using adsorption and reaction energies. Stability was found along the (111) Miller index for all tested alloys. Strong surface adsorption was observed on PtPd (111) and PtPd3 (111) surfaces, while weaker adsorption occurred on Pt7Pd (111) surfaces. Lower activation energies were observed on Pt7Pd (111) and Pt3Pd (111) surfaces for the rate-determining step (O* + H* → *OH), compared to pristine Pd (111). In contrast, the *OH formation step was inhibited on PtPd (111) and PtPd3 (111) surfaces due to strong surface absorption of reaction intermediates. Overall, Pt3Pd (111) and Pt7Pd (111) surfaces are promising alternative catalysts for H2/O2 recombination, especially in the rate-determining *OH formation step.

Nanoporous Carbon-Supported Bimetallic (Ni, Cu, and Fe)-Mo Catalysts for Partial Hydrogenation of Biodiesel.

Upgrading biodiesel or hydrogenated fatty acid methyl esters (H-FAMEs) by partial hydrogenation is a second-generation biofuel with high specific fuel characteristics, such as superior cold flow properties, higher oxidative stability, and lower hazardous gas emissions, allowing this biofuel to provide excellent fuel properties, over conventional biodiesel. This study assessed the potential of using nanoporous carbon produced from cattail leaves (CL) as an alternative catalyst support. We synthesized various catalysts including monometallic Mo/NPC, Ni/NPC, Ce/NPC, and Fe/NPC catalysts, as well as bimetallic molybdenum-based catalysts doped with nickel, copper, or iron for the partial hydrogenation of soybean biodiesel. The NPC support demonstrated a surface area (S BET) of approximately 1,323 m2g-1, which greatly increases the catalytic activity through the efficient dispersion of catalyst active sites. The partial hydrogenation reaction of soybean FAME over the MoNi/NPC catalyst obtained the highest catalytic activity with enhanced oxidation stability from 3 to 14 h, and the cloud point and pour point increased from 2 to 13 °C and -1 to 10 °C, respectively. Hence, the selection of catalysts is crucial due to their impact on the feasibility of the process and its economic viability. This article focuses on highlighting the effectiveness of a highly promising catalyst for partial hydrogenation as well as examining the variables that influence the primary reaction pathway.

Palladium-Functionalized Nanostructured Nickel-Cobalt Oxide as Alternative Catalyst for Hydrogen Sensing Using Pellistors.

To meet today's requirements, new active catalysts with reduced noble metal content are needed for hydrogen sensing. A palladium-functionalized nanostructured Ni0.5Co2.5O4 catalyst with a total Pd content of 4.2 wt% was synthesized by coprecipitation to obtain catalysts with an advantageous sheet-like morphology and surface defects. Due to the synthesis method and the reducible nature of Ni0.5Co2.5O4 enabling strong metal-metal oxide interactions, the palladium was highly distributed over the metal oxide surface, as determined using scanning transmission electron microscopy and energy-dispersive X-ray investigations. The catalyst tested in planar pellistor sensors showed high sensitivity to hydrogen in the concentration range below the lower flammability limit (LFL). At 400 °C and in dry air, a sensor response of 109 mV/10,000 ppm hydrogen (25% of LFL) was achieved. The sensor signal was 4.6-times higher than the signal of pristine Ni0.5Co2.5O4 (24.6 mV/10,000 ppm). Under humid conditions, the sensor responses were reduced by ~10% for Pd-functionalized Ni0.5Co2.5O4 and by ~27% for Ni0.5Co2.5O4. The different cross-sensitivities of both catalysts to water are attributed to different activation mechanisms of hydrogen. The combination of high sensor sensitivity to hydrogen and high signal stability over time, as well as low cross-sensitivity to humidity, make the catalyst promising for further development steps.

Substoichiometric La0.8MnO3-based nanocomposites for PGM-free activation of CH4: Ni or Cu? Surface or bulk?

Methane is a renewable fuel when derived from biogas upgrading or by CO2 capture and utilization, with the possibility of fully replacing natural gas in the already established gas infrastructure and engines. However, being a potent greenhouse gas, its use as fuel demands a sustainable activation procedure, to convert any residual traces of unburned CH4 into CO2, a challenging reaction especially at near-stoichiometric conditions typical of Three-Way Catalytic systems (TWC). To avoid expensive noble metals, we developed cheaper alternative catalysts: A-site deficient LaMnO3-based nanocomposites incorporating Ni and Cu. These elements were introduced either as B-site dopants in the perovskite lattice or deposited via Ammonia-driven Deposition-Precipitation (ADP) on the perovskite surface, in both cases yielding metal nanoparticles (NPs) after a reductive treatment. Characterization encompassed various techniques: XRD, N2 physisorption, SEM-EDX, XPS, H2-TPR, HAADF STEM-EDX. CH4 oxidation to CO2 under stoichiometric O2 served as the probe reaction, as model for TWC conditions in methane-fed engines. The LaMn-perovskite itself displayed a promising activity thanks to favourable morphological and redox features (50 % and 90 % CH4 conversion at 581 °C and 678 °C, respectively); further improvements could be obtained upon Ni and Cu loading. The best performances were achieved by: i) the catalyst prepared by Ni-ADP (50 % and 90 % CH4 conversion at 517 °C and 635 °C), featuring high Ni surface concentration and NPs density and a synergy with the perovskite support, as opposed to the low Ni surface concentration on B-site doped samples; ii) the reduced Cu-doped catalyst (50 % and 90 % CH4 conversion at 508 °C and 645 °C), thanks to the high activity of reduced Cu species, the low NPs size and good metal-support interaction, in contrast to the strong NPs agglomeration of the Cu-ADP catalyst. Among the two most active catalysts, a better long-term stability was retained by the Cu-doped sample. This work laid the foundation for the development of alternative CH4 oxidation catalysts at the stoichiometric air-to-fuel ratio, cheaper than commercial Pd-based ones.

Synergistic effects of carbon nanotubes on α-MnO2 electrocatalysts for improved oxygen reduction in alkaline fuel cells

The Alkaline Membrane Fuel Cell (AMFC), is a device crucial for electrochemical energy production through the oxygen reduction reaction (ORR), conventionally relies on platinum catalysts. However, the challenges of excessive cost and inadequate stability in alkaline environments have hindered its widespread commercialization. Alpha manganese dioxide (αMnO2), with diverse applications in energy and environmental domains, has potential as an alternative catalyst due to its lower metal costs and comparable catalytic activity. This study focuses on the synthesis of αMnO2 nanotubes through controlled environment temperature, and integration with carbon nanotubes (CNTs). Optimizing the gas pressure and temperature during synthesis resulted in structural changes in αMnO2 nanotubes, with a notable increase in catalytic behavior at elevated temperatures. The sample treated at 450 °C and mixed with CNTs (CNT-MO450) demonstrated outstanding ORR performance and prolonged stability in an alkaline medium. Furthermore, the CNT-MO450 exhibited the highest current density of −5.2 mA/cm2 at a potential of 0.65 V vs RHE, a peak power density of 73 mW/cm2 (comparable to Pt/C at 95 mW/cm2), and a charge transfer resistance of 310 Ω. The temperature treatment affected the αMnO2 nanotubes, which resulted in increased length at an optimal temperature, leading to a larger surface area. This enhancement in surface area is crucial to improved catalytic activity, electrical conductivity, and extended stability during operation in alkaline media. The findings suggest that CNT-MO450 catalysts hold promise as a cost-effective and stable alternative catalyst for AMFCs.

EcNikA, a versatile tool in the field of artificial metalloenzymes

This review describes the multiple advantages of using of EcNikA, a nickel transport protein, in the design of artificial metalloenzymes as alternative catalysts for synthetic biology. The rationale behind the strategy of artificial enzyme design is discussed, with particular emphasis on de novo active site reconstitution. The impact of the protein scaffold on the artificial active site and thus the final catalytic properties is detailed, highlighting the considerable aptitude of hybrid systems to catalyze selective reactions, from alkene to thioether transformations (epoxidation, hydroxychlorination, sulfoxidation). The different catalytic approaches – from in vitro to in cristallo – are compared, revealing the considerable advantages of protein crystals in terms of stabilization and acceleration of reaction kinetics. The versatility of proteins, based on metal and ligand diversity and medium/physical conditions, are thus illustrated for oxidation catalysis.

Ensuring Stability of Anode Catalysts in PEMWE: From Material Design to Practical Application.

Proton Exchange Membrane Water Electrolysis (PEMWE) has emerged as a clean and effective approach for the conversion and storage of renewable electricity, particularly due to its compatibility with fluctuating photovoltaic and wind power. However, the high cost and limited performance of iridium oxide catalysts (i.e. IrO2) used as anode catalyst in industrial PEM electrolyzers remain significant obstacles to widespread application. Although numerous low-cost and efficient alternative catalysts have been developed in laboratory research, comprehensive stability studies critical for industrial use are often overlooked. This leads to the failure of performance transfer from catalysts tested in liquid half-cell systems to those employed in PEM electrolyzers. This concept presents a thorough overview for the stability issues of anode catalysts in PEMWE, and discuss their degradation mechanisms in both liquid half-cell systems and PEM electrolyzers. We summarize comprehensive protocol for the assessment and characterization, analyze the effective strategies for stability optimization, and explore the opportunities for designing viable anode catalysts for PEM electrolyzers.

Ni and Co-based bifunctional electrocatalysts supported on TiO2@C for oxygen evolution and reduction reactions

In the search for affordable, ecofriendly, and sustainable catalysts for energy-related processes, series of Ni and Co-based bifunctional hybrid electrocatalysts supported on TiO2@C were prepared and studied in the oxygen evolution (OER) and oxygen reduction reactions (ORR). The hybrid TiO2@C supports were prepared using three biomass precursors: furfural, chitosan and saccharose. The nature and dispersion of the metallic phases on those supports was evaluated as a function of the biomass-derived precursors. The prepared materials showed electrocatalytic activity towards ORR and OER reaction, being more active for the latter. Despite a lower performance than Pt/C benchmark, these materials are clearly at much lower costs. The long-term stability and performance of the catalysts were also performed. The number of electrons involved in both processes was determined and a mechanism is proposed for the understanding of the mechanism of reactions using the present materials. It can be concluded that the Ni and mainly Co-based electrocatalysts show a remarkable potential for use as alternative catalysts in fuel cells-related reactions.

Low‐Temperature Ammonia Decomposition over Sm2O3 Supported Non‐Noble Metal (Fe, Co, and Ni) Catalysts

AbstractThe generation of hydrogen from ammonia has arisen great interests along with the flourish of hydrogen energy. The widely utilization of ruthenium in catalyzing ammonia decomposition has triggered research on the development of alternative catalysts based on more readily available non‐noble metals. Herein, a series of non‐noble metal catalysts with Co/Ni/Fe nanoparticles anchored on Sm2O3 nanorods are developed via a facile precipitation method, which can effectively catalyze ammonia decomposition at temperatures below 600 °C. Among these non‐noble catalysts, Co/Sm2O3 performs the best and achieves a constant H2 production rate of 163 mmolH2/gCo/min for more than 100 hours under the condition of 550 °C and WHSV=15000 mL/gcat/h, which exceeds most of the recently reported Co‐based catalysts. Further characterizations have disclosed that such superior catalytic performance should originate from the improved interaction between non‐noble metals and Sm2O3 support. These findings not only provide a series of active and robust non‐noble catalysts for catalyzing ammonia decomposition at relatively low temperatures, but also manifest the effect of rare earth oxides in regulating the geometric and electronic properties of non‐noble metals through metal‐support interactions.

Heterogeneous degradation of chloramphenicol antibiotic by peroxymonosulfate activated by FeS and FeS2: Mechanism and effects of catalysts dosage and pH

Antibiotics in the environmental waters pose long-term threat to ecological safety because of their persistent and potential toxic nature. FeS and FeS2 were proved to be efficient catalysts for the activation of peroxymonosulfate (PMS) and the generation of sulfate radical generation for refractory pollutant degradation. However, their performance for antibiotic degradation has not yet been comparatively and comprehensively investigated. Herein, the FeS/PMS and FeS2/PMS systems were developed to explore chloramphenicol (CAP) degradation under equal conditions. The results show that CAP was efficiently degraded in both two systems, with a removal efficiency exceeding 90 % within 120 min using 6 mM PMS and 0.6 g/L catalysts.Acceleration in degradation rate was observed in the FeS2/PMS system when the catalyst dosage ranged from 0.1 g/L to 1.0 g/L (constant PMS concentration) with a reaction rate constant (kobs) of 2.1-fold higher than that in the FeS/PMS system. However, the kobs were comparable with the PMS concentration range (constant catalyst dosage) in the two systems, suggesting that the catalysts were the rate-limiting step in CAP degradation process. The initial pH strongly affected CAP degradation in the FeS/PMS system but had little effect on that in the FeS2/PMS system. Surface Fe2+ played a dominant role in PMS activation, and S22−/S2− facilitated Fe2+ regeneration. Further, both FeS and FeS2 had stable activity for PMS activation during long-term use. This study proves the effectiveness of FeS and FeS2 for PMS activation for antibiotic degradation and differentiates their catalytic qualities, which will provide alternative heterogeneous catalysts for practical application.

Nature of the Active Center for the Oxygen Reduction on Ag-Based Single-Atom Alloy Clusters.

The development of alternative alloy catalysts with high activity, surpassing platinum group metals, for the oxygen reduction reaction (ORR) is urgently needed in the field of electrocatalysis. The Ag-based single-atom alloy (AgSAA) cluster has been proposed as a promising catalyst for the ORR; however, enhancing its activity under operational conditions remains challenging due to limited insights into its actual active site. Here, we demonstrate that the operando formation of the MO x (OH) y complex serves as the key active site for catalyzing the ORR over AgSAA cluster catalysts, as revealed through comprehensive neural network potential molecular dynamics simulations combined with first-principles calculations. The volcano plot of the ORR over the MO x (OH) y complex addresses the gaps inherent in traditional metallic alloy models for pure AgSAA cluster catalysts in ORR catalysis. The appropriate orbital hybridization between OH and the dopant metal in the MO x (OH) y complexes indicated that the Ag54Co1, Ag54Pd1, and Ag54Au1 clusters are optimal AgSAA catalysts for the ORR. Our work underscores the significance of theoretical modeling considering the reaction atmosphere in uncovering the true active site for the ORR, which can be extended to other reaction systems for rational catalyst design.