Inexpensive Catalyst Research Articles

Sterilization and Long-Term Stability of Cobalt Intercalated MnO₂ Catalyst in the Cathode of Separator-Free Microbial Fuel Cells

Microbial Fuel Cells (MFCs) are a promising technology that can simultaneously address recent energy shortages and wastewater treatment problems for freshwater production. Recently, inexpensive Pt-free catalysts have been investigated to improve the cathode performance of MFCs. In this study, birnessite manganese oxide intercalated a cobalt (Co-MnO₂) catalyst to make the cathode sterilizable. The use of a bactericidal cathode is expected to improve output by suppressing electron transfer from microorganisms to the cathode, which is the cause of MFC performance degradation, and by eliminating the separator that limits proton transfer. The MFC with Co-MnO₂ catalyst on the cathode achieved a maximum power density of 110 μW/cm². In addition, the function of the Co-MnO₂ catalyst did not degrade for at least 158 days.

K-promoted cobalt-based catalysts for heterogeneous hydroformylation

K-promoted Co/SiO2 catalysts were developed for heterogeneous olefin hydroformylation. Through various characterization techniques, the promotional effect of the K promoter in enhancing oxygenate selectivity was investigated.

Electrochemical reconstruction of a 1D Cu(PyDC)(H2O) MOF into in situ formed Cu-Cu2O heterostructures on carbon cloth as an efficient electrocatalyst for CO2 conversion.

Electrochemical carbon dioxide (CO2) conversion has enormous potential for reducing high atmospheric CO2 levels and producing valuable products simultaneously; however the development of inexpensive catalysts remains a great challenge. In this work, we successfully synthesised a 1D Cu-based metal-organic framework [Cu(PyDC)(H2O)], which crystallizes in an orthorhombic system with the Pccn space group, by the hydrothermal method. Among the different catalysts utilized, the heterostructures of cathodized Cu-Cu2O@CC demonstrate increased efficiency in producing CH3OH and C2H4, achieving maximum FE values of 37.4% and 40.53%, respectively. Also, the product formation rates of CH3OH and C2H4 reach up to 667 and 1921 μmol h-1 cm-2. On the other side, Cu-Cu2O/NC-700 carbon composites simultaneously produced C1-C3 products with a total FE of 23.27%. Furthermore, a comprehensive study involving detailed DFT simulations is used to calculate the energetic stability and catalytic activity towards the CO2 reduction of Cu(111), Cu2O(111), and Cu@Cu2O(111) surfaces. During the early phase of electrochemical treatment, Cu(II) carboxylate nodes (Cu-O) in the Cu(PyDC)(H2O) MOF were reduced to Cu and Cu2O, with a possible synergistic enhancement from the PyDC ligands. Thus, the improved activity and product enhancement are closely associated with the cathodized reconstruction of Cu-Cu2O@CC heterostructures on carbon cloth. Hence, this study provides efficient derivatives of Cu-based MOFs for notable electrocatalytic activity in CO2 reduction and gives valuable insights towards the advancement of practical CO2 conversion technology.

Aluminized polyborate catalyzed efficient solvent-free synthesis of 1,8-dioxo-decahydroacridines via hantzsch condensation

In this work we report, aluminized polyborate catalyzed facile and efficient one-pot four component Hantzsch synthesis of 1,8-dioxo-decahydroacridines using substituted aromatic aldehydes (1 mmol), dimedone (2 mmol) and ammonium acetate (1.5 mmol) at 95-100oC under solvent-free condition. The prominent advantages of this methodology are good product yields (85-95%), eco-friendliness, mild reaction conditions and use of inexpensive catalyst. The structures of the targeted molecules were examined by FT-IR, 1H-NMR and mass spectral techniques.

Dehydrative alkynylation of 3-hydroxyisoindolinones with terminal alkynes for the synthesis of 3-alkynylated 3,3-disubstituted isoindolinones.

A brand-new procedure for the synthesis of 3-alkynylated 3,3-disubstituted isoindolinones has been disclosed via a HOTf or Fe(OTf)3-catalyzed dehydrative alkynylation of 3-hydroxyisoindolinones with terminal alkynes. Aryl, alkenyl and alkyl terminal alkynes are suitable to couple with a broad range of 3-hydroxyisoindolinones to afford the desired products in moderate to good yields. This protocol features the use of an inexpensive catalyst, mild reaction conditions, broad substrate scope and easy elaboration of the products.

The catalytic performance of (ZrO)n (n = 1-4, 12) clusters for Suzuki-Miyaura cross-coupling: a DFT study.

Superatoms are special clusters with similar physicochemical properties to individual atoms in the periodic table, which open up new avenues for exploring inexpensive catalysts. Given that the ZrO superatom possesses the same number of valence electrons as a Pd atom, the mechanisms of the Suzuki-Miyaura reaction catalyzed by (ZrO)n (n = 1-4) clusters have been investigated and compared with the corresponding Pdn (n = 1-4) species to explore superatom-based catalysts for the formation of C-C bonds via a density functional theory (DFT) study. It was interesting to find that the catalytic activities of (ZrO)n (n = 1-4) towards the Suzuki-Miyaura reaction gradually improved as the cluster size increased. Therefore, to obtain more efficient catalysts, the catalytic activity of a well-designed (ZrO)12 nanocage towards this cross-coupling reaction has been further evaluated. Gratifyingly, this nanocage shows excellent catalytic performance for the considered coupling reaction, which is even comparable to that of the commonly used Pd catalyst and outperforms the corresponding Pd12 cluster. We hope this study can not only provide valuable guidance for the development of noble metal-like catalysts for C-C bond formation, but also expand the application of superatoms in the catalysis of organic reactions.

Hydrogen production from complete dehydrogenation of hydrazine borane on carbon-doped TiO2-supported NiCr catalysts

C-doped mesoporous TiO2-supported Cr(OH)3 modified Ni nanoparticles (Ni–Cr/CTO) with different morphologies were synthesized by a simple wet-chemical method and used as efficient catalysts for hydrogen production from hydrazine borane.

Synthesis of novel hollow carbon nanotubes @ Co-Fe alloy/iron phthalocyanine electrocatalyst by self-assembly method for OER and ORR study

The exploration of an inexpensive catalyst with effective oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activities to replace precious metal electrocatalysts has been of great interest in recent years. In this paper, CNT@Co-Fe/FePc composites were synthesized with high efficiency using a self-assembly strategy. In the synthesis process, carbon nanotubes (CNTs) were synthesized as the base material using crab shells as templates and honey as the carbon and nitrogen source. CoFe alloy nanoparticles derived from CoFe-based prussian blue analogs were self-assembled and anchored on CNTs, and then iron phthalocyanine with Fe-N4 portion was coupled with CNTs by π-π stacking. Finally formed a homogeneous and stable composite material. The self-assembly method is simple and efficient to achieve good metal loading. The prepared CNT@Co2-Fe1/FePc exhibits excellent catalytic performance and stability for OER and ORR in alkaline electrolyte. The overpotential at 10 mA cm−2 of CNT@Co2-Fe1/FePc for OER is 343 mV with a very small Tafel slope of 43.59 mV dec−1. CNT@Co2-Fe1/FePc has high methanol tolerance and persistence for ORR. This work provides a strategy for the construction of transition metal-carbon composite electrocatalytic materials with excellent catalytic performance and stability for OER and ORR reactions.

Investigation of NiCoOx catalysts for anion exchange membrane water electrolysis: Performance, durability, and efficiency analysis

Anion exchange membrane (AEM) water electrolysis is a promising method for hydrogen production using inexpensive metal oxide catalysts. This study investigates the catalytic activity and performance of nickel cobalt oxide (NiCoOx) catalysts in AEM water electrolysis for hydrogen production. The catalysts were synthesized with varying ratios of Ni to Co. The NiCoOx catalysts were coated on nickel foam gas diffusion layer (GDL) at the anode. Scanning electron microscopy (SEM) analysis revealed a distinct flaky structure of the NiCoOx catalyst. X-ray diffraction (XRD) studies confirmed the presence of NiCo2O4 spinel crystal structure in the catalysts. Linear sweep voltammetry (LSV) measurements for Oxygen evolution reaction (OER) in three electrode systems showed that NiCoOx (1:3) exhibited the highest catalytic activity, with a current density of 238 mA cm−2 at 1.8 V. Tafel analysis indicated that NiCoOx (1:3) had the lowest Tafel slope, suggesting faster reaction kinetics and lower overpotential for higher current density. Chronoamperometry tests demonstrated the stability of the catalysts at various current densities, and long-term stability testing of NiCoOx (1:3) for 500 h revealed minimal voltage increase during OER, demonstrating its stability in prolonged operation. NiCoOx (1:3) displayed the highest activity among the catalysts at different temperatures, with current densities reaching 1700 mA cm−2 at 2.2 V and 70 °C for single-cell electrolysis. The Nyquist plots and equivalent circuit analysis reveal that the NiCoOx (1:3) catalyst exhibits lower activation resistance and higher efficiency in oxygen evolution reaction compared to other catalyst compositions. Temperature-dependent measurements demonstrate decreased resistances (ohmic, activation, and membrane) with increasing temperature, indicating improved reaction kinetics and ion conductivity. Long-term durability tests reveal the stable operation of the catalyst, while short-term tests confirm its effectiveness at higher current densities for single-cell electrolyzer operation. These findings highlight the importance of electrochemical Impedance Spectroscopy (EIS) and equivalent circuit fitting in optimizing AEM water electrolysis performance, aiding the development of efficient and durable electrolyzers for hydrogen production.

Zn-Based Catalysts for Selective and Stable Electrochemical CO2 Reduction at High Current Densities

The development of low-cost and stable catalysts is important for lowering the capital and operational cost of CO2 electro-reduction (ECR). Zinc (Zn) is an earth-abundant metal, with promising performance for the CO2-to-CO conversion.1 Zinc oxide (ZnO) has been recently employed for the CO2-to-CO conversion, recording promising selectivity (FECO) but short-term stability, in Flow-Cell configuration.2,3 ZnO phase has been proven critical for competent ECR performance, since both the oxidation state of Zn and the Zn/ZnO interface are proven critical for high FECO. 4,5In our work 6, we have synthesised various ZnO allotropes, the properties of which induced differences in their ECR performance. We have identified the ZnO nanorods (ZnO-NR) as the best performing catalyst. The latter was implemented in a zero-gap ECR electrolyser (MEA), recording partial current density for CO (jCO) of 160 mA cm-2 at cell voltage of 3.6 V. We have correlated the depletion of the ZnO phase in the MEA with the degradation of the performance (initially 15 h stability). We applied a periodic oxidation protocol in the MEA, causing the regeneration of ZnO-phase, allowing us to prolong the life-time of the catalyst. Through our strategy we were able to record 82% CO selectivity (FECO) for over 100 h, at -160 mA cm-2. This work provides an approach of practical use of inexpensive Zn-based catalysts for large-scale ECR applications.(1) Luo, W.; Zhang, J.; Li, M.; Züttel, A. Boosting CO Production in Electrocatalytic CO2 Reduction on Highly Porous Zn Catalysts. ACS Catal. 2019, 9 (5), 3783–3791. https://doi.org/10.1021/acscatal.8b05109.(2) Zeng, J.; Fontana, M.; Sacco, A.; Sassone, D.; Pirri, C. F. A Study of the Effect of Electrode Composition on the Electrochemical Reduction of CO2. Catalysis Today 2021. https://doi.org/10.1016/j.cattod.2021.07.014.(3) Zong, X.; Jin, Y.; Li, Y.; Zhang, X.; Zhang, S.; Xie, H.; Zhang, J.; Xiong, Y. Morphology-Controllable ZnO Catalysts Enriched with Oxygen-Vacancies for Boosting CO2 Electroreduction to CO. Journal of CO2 Utilization 2022, 61, 102051. https://doi.org/10.1016/j.jcou.2022.102051.(4) Nguyen, D. L. T.; Jee, M. S.; Won, D. H.; Jung, H.; Oh, H.-S.; Min, B. K.; Hwang, Y. J. Selective CO2 Reduction on Zinc Electrocatalyst: The Effect of Zinc Oxidation State Induced by Pretreatment Environment. ACS Sustainable Chem. Eng. 2017, 5 (12), 11377–11386. https://doi.org/10.1021/acssuschemeng.7b02460.(5) Geng, Z.; Kong, X.; Chen, W.; Su, H.; Liu, Y.; Cai, F.; Wang, G.; Zeng, J. Oxygen Vacancies in ZnO Nanosheets Enhance CO2 Electrochemical Reduction to CO. Angewandte Chemie International Edition 2018, 57 (21), 6054–6059. https://doi.org/10.1002/anie.201711255.(6) Stamatelos, I.; Dinh, C.-T.; Lehnert, W.; Shviro, M. Zn-Based Catalysts for Selective and Stable Electrochemical CO2 Reduction at High Current Densities. ACS Appl. Energy Mater. 2022. https://doi.org/10.1021/acsaem.2c02557. Figure 1

Strategies for Sustainable Fuel Production Via Photoelectrochemical Synthesis

Developing sustainable energy is highly imperative for humankind owing to the drastic rise in world population and the proportional rise in energy demand at the expense of energy consumption. Various efforts have been made to explore, generate, store, and utilize renewable energy to replace fossil fuels. Among them, solar energy is considered an alternative to fossil fuels because it is inexhaustible, clean, cost-effective, and versatile. Interestingly, this prime source provides massive energy that is high enough (1.9 × 108 TWh/yr) to counterattack global energy consumption (1.3 × 105 TWh/yr).Photoelectrochemistry has been considered a promising route to harness this incredible energy by producing sustainable energy fuels and carriers such as hydrogen, hydrocarbon, and ammonia. PEC systems have the great advantages of simple process steps and very low environmental burdens. However, this technology must overcome many challenges regarding commercial applications, particularly in fabricating electrode materials for PEC water splitting.One of the most important challenges to overcome this problem is discovering efficient catalysts for implementing photoelectrochemical (PEC) fuel production. A critical requirement for outstanding catalysts is an ability to boost the kinetics of a chemical reaction and durability against electrochemical and photo-induced degradation. Moreover, the charge-separation and transfer mechanism are the two paramount properties to consider while designing photoelectrodes. Briefly, the semiconductor materials to be used in PEC water splitting must possess a conduction band potential more negative than the reduction edge of hydrogen and a valence band potential positive to actuate water oxidation. In practice, the photocurrent density and solar-to-hydrogen (STH) efficiency of the n-type semiconductors are far behind the theoretical values.To address this critical and long-standing technical barrier, I have focused on an intense search for efficient, durable, and inexpensive alternative catalysts with moderate band gap, efficient charge excitation-separation property, and high solar energy conversion efficiency for photoelectrochemical systems of water splitting, hydrocarbon conversion, and ammonia production. Keywords : Photoelectrochemistry, Sustainable Energy, Water Splitting, Ammonia synthesis, Urea synthesis, Hydrocarbon

Ni-Fe-S Supported on Mo-Based Mxene (Mo2CTx) As a High-Performance Bifunctional Electrocatalyst for Rechargeable Zinc–Air Batteries

Rechargeable Zn-air batteries are a promising alternative to lithium-ion batteries due to their high theoretical energy density (1350 Wh kg−1), low cost, and environmental benefits. To meet the growing demand on renewable power for electric vehicles and sustainable goals, inexpensive and efficient bifunctional catalysts with both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities have recently garnered a great interest in energy conversion fields. MXene, a rising family of two-dimensional (2D) materials, particularly Mo2CTx, has been identified as a promising electrocatalyst supporter. The tunable surface chemistry, atomic thickness, and high surface area of the MXene architecture reduce the reaction barrier by enhancing the conductivity, exposing active sites and increasing the reaction rate in charge transfer and gas/ion diffusion process. Therefore, with coexistence of MXene platform, favorable reaction conditions can be created to facilitate the catalyst's performance.In this study, a novel bifunctional electrocatalyst of Ni-Fe sulfide uniformly embedded in a Mo-based MXene (Mo2CTx) sheet structure is designed for Zn-air battery applicaiton. Surface characterization shows that 2-D Mo2CTx nanosheets can be successfully fabricated by hydrothermal etching method. The deposition of Ni-Fe sulfide nanocatalysts onto Mo2CTx MXene nanosheets exhibits excellent electrochemical performance, which is attributed to the enhanced intrinsic activity due to rapid electron transfer from MXene, abundant functional groups on the surface to lower the reaction activity energy. In addition, the architecture of MXene support provides a large specific surface area, high porosity, good conductivity and highly exposed active sites. When using MXene supported Ni-Fe-S nanocatalysts as the electrode materials for Zn-air battery application, a high peak power density at 107.24 mW cm−2 with superior cycle stability within 200h is obtained. Moreover, the possible mechanisms on energy storage is also proposed. These results clearly indicates the successfully development of an exciting bifunctional electrocatalyst for electrochemical energy conversion applications.

Rationalizing the Effect of the Redox-Inactive Metals on the Activity of Oxides in Oxygen Electrocatalysis

The large-scale implementation of renewable energy conversion and storage technologies is a key challenge to transition to a sustainable society. One of the most critical elements towards this goal is the discovery of active, stable and inexpensive catalysts for electrochemical energy conversion processes, such as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are central for the efficiency of water-splitting electrolyzers, fuel cells and metal–air batteries.1 Manganese-based spinels, MxMn3-xO4, and ruthenium pyrochlores, M2Ru2O7 − δ, are known as active catalysts for the ORR and OER, respectively, and were studied here as model systems to rationalize the effect of the incorporation (doping) of redox-inactive elements (M) into the structure on the catalytic performance of complex oxides in oxygen electrocatalysis.We found a direct correlation between the ORR/OER activity of Mn3O4:M spinels (M = Mn, Cu, Zn, Mg, Ca, Sr),2 and Y1.8M0.2Ru2O7 − δ pyrochlores (M = Y, Fe, Co, Ni, Cu),3 the lattice oxygen binding strength/lability and the formation enthalpy of the binary MO x oxides. We found experimentally that the activity of Mn3O4:M and Y1.8M0.2Ru2O7 − δ in, respectively, ORR and OER, varies significantly depending on the nature of M. We observed that metals M with higher enthalpies of formation for the respective oxide weaken the oxygen binding on the surface of the complex oxide that correlates in turn with changes in ORR/OER activity. DFT studies captured changes in the electronic structure upon M substitution and allowed to correlate trends in the electronic band structure and the oxygen vacancies formation energies with the ORR/OER performance of the Mn3O4:M/Y1.8M0.2Ru2O7 − δ catalysts. These activity trends are subsequently discussed in the framework of theoretically established correlations between the electrocatalytic activity and adsorption energies of catalytic intermediates. We demonstrated that the introduction of redox-inactive metal substituents/dopants into the host structure of a metal oxide is a highly versatile approach to tune the binding strength of reaction intermediates (determining the position of the catalyst on the ORR/OER activity volcano), and in turn improve the ORR/OER activity and also selectivity. This approach is a general concept that is transferrable to a broad selection of materials and processes associated with adsorption and redox reactions involving oxygen species.References(1) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Science 2017, 355, eaad4998.(2) Wu, Y.-H.; Mehta, H.; Willinger, E.; Yuwono, J. A.; Kumar, P. V.; Abdala, P. M.; Wach, A.; Kierzkowska, A.; Donat, F.; Kuznetsov, D. A.; Müller, C. R. Angew. Chem. Int. Ed. 2023, 62, e202217186.(3) Kuznetsov, D. A.; Naeem, M. A.; Kumar, P. V.; Abdala, P. M.; Fedorov, A.; Müller, C. R. J. Am. Chem. Soc. 2020, 142, 7883-7888.

(Invited) Designing Advanced Low-PGM Core-Shell Electrocatalysts for Fuel Cells and Electrolyzers

The low-content Pt-based core-shell catalysts potentially alleviate the drawback in the existing Pt catalysts (i.e., high cost, slow kinetics, poor stability, etc.) and further improve the oxygen reduction reaction (ORR) activity and stability for the proton exchange membrane fuel cells (PEMFCs).1 There have been remarkable advances in both the development of promising core−shell catalysts and the understanding of the fundamental catalytic mechanisms, and it is clear that some of the low platinum-group-metal (PGM) core−shell catalysts with enhanced activity and stability have great potential for use in PEMFCs. Nevertheless, various issues still need to be clearly addressed for the advanced core−shell catalysts of the future. On the other hand, PEM electrolyzers (ELs) are desirable large-scale energy devices to produce green hydrogen toward a net-zero carbon economy. The technologies require the availability of effective catalysts, particularly for the oxygen evolution reaction (OER). However, Ir- and Ru-based catalysts are currently the best-performing OER catalysts and their cost and limited availability hamper the widespread commercialization/deployment of PEMELs. Therefore, there is also an urgent need for developing highly durable and inexpensive catalysts for the OER. This talk first focuses on synthetic strategies, catalytic mechanisms, and influencing factors of Pt- and Ir-based catalysts used for PEMFCs and PEMELs. We will then discuss effective and solid strategies/designs to employ transition-metal-nitride-based cores for the development of highly advanced low-PGM core-shell catalysts for the ORR, particularly in heavy-duty vehicle (HDV) PEMFC applications, and for the OER in PEMEL applications. R. Zhao and K. Sasaki, Advanced Pt-Based Core-Shell Electrocatalysts for Fuel Cell Cathodes, Accounts of Chemical Research. 55 (2022) 1226-1236.

Phosphorus-doped nickel-gallium alloy and Ti4O7 nanofibers: A novel self-supporting bifunctional catalyst for oxygen electrocatalysis and Zn-air batteries

Precious metal catalysts are widely recognized for their excellent efficiency in OER and ORR, but high cost and stability limit further commercial expansion. Carbon-based catalysts with large specific surface area, although a potential alternative to noble metal catalysts in terms of price and performance, are notoriously weak in terms of corrosion resistance in extreme environments. Metal catalysts are able to solve the above problems and are gradually coming into the limelight, but the control of morphology is not as good as that of carbon-based catalysts. Therefore, in order to solve the above problems together, the development of bifunctional catalysts with high efficiency, stability, low cost and excellent morphology has become a bright research direction. In this study, a new catalyst consisting of phosphorus-doped self-supported nanostructured Ti4O7 and nickel-gallium alloy particles was investigated using an electrostatic spinning process. Most of the previous studies have simply prepared Ti4O7 nanofibers without in-depth investigation on how to better control their morphology. In contrast, this study presents a universal set of experimental parameters for the development of very fine Ti4O7 nanospinning. With the help of this set of parameters, we develop a novel Ti4O7/C composite substrate nanofiber catalyst with an average diameter less than 297 nm. Its excellent morphology and corrosion resistance make it an inexpensive bifunctional catalyst with great potential. Relevant OER performed in 1 M KOH electrolyte shows that the catalyst has a low Tafel slope (80.77 mV dec−1), a small overpotential (282 mV at 10 mA cm−2), and excellent stability (up to 5000 cycles). In a strongly alkaline environment, the catalyst outperforms commercially available RuO2 (299 mV and 105.79 mV dec−1). In addition, the catalyst demonstrates a half-wave potential of 0.86 V in 0.1 M KOH electrolyte, exhibiting excellent ORR performance. The maximum power density (161 mW cm−2) and energy density (813 mA h gZn−1) of the zinc-air battery assembled with this catalyst exceeds the performance of the air battery using the Pt/C catalyst with better stability. In summary, this study achieves significant methodological advances and develops a novel bifunctional catalyst, which is of interest to a wide range of researchers.

Solid-phase microwave synthesis of high-entropy graphene quantum dots as metal-free electrochemical catalysts

In this study, high-entropy graphene quantum dots (GQDs) are synthesized and utilized as metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline electrolyte. An efficient solid-state microwave route was used to synthesize the GQD catalysts. This synthesis method involves the pyrolysis of two carbon precursors and four dopant precursors under a pulse microwave irradiation at 180 °C. The synthesized efficient catalyst possesses an average particle size of about 5 nm. The synthesized GQDs catalyst contains six elements in the graphite-like lattices with numerous surface functionalities and dopants. Synthesized high-entropy GQD catalytic electrodes displayed ultra-high electrochemically active surface area and endurance for the ORR measurements. The GQD electrode shows a well-defined reduction peak at ca. −0.5 V and an onset potential at ca. −0.1 V vs. saturated calomel electrode in the diluted potassium hydroxide solution. The heteroatom doping into the GQD nanostructure greatly increased the ORR catalytic activity. The above synthesized non-metallic and inexpensive catalyst showed remarkable properties such as enhanced catalytic activity, selectivity, and superior durability. Therefore, synthesized GQD electrodes have great potential for energy applications, especially for fuel cells.

Green Synthesis of Electrophilic Alkenes Using a Magnesium Catalyst under Aqueous Conditions and Mechanistic Insights by Density Functional Theory.

A green approach for the synthesis of electrophilic alkenes has been developed via Knoevenagel condensation between active methylene compounds and carbonyl compounds using Mg powder under aqueous conditions. In this strategy, Mg(OH)2 acts as a catalyst, which was generated in situ by the reaction between metallic Mg (20 mol %) and water. Mg was found to be an efficient, nontoxic, and inexpensive metal catalyst system for producing a range of electrophilic alkenes in excellent yields (≤98%). A gram-scale synthesis of electrophilic alkenes has been developed, and Mg metal was recovered and recycled up to three times without an appreciable loss of catalytic activity. A catalytic cycle was proposed, and the reaction mechanism was investigated using density functional theory. The key steps are enolization of ethyl cyanoacetate, C-C bond formation, and then regeneration of the catalyst via metathesis with H2O. The overall reaction occurs easily with a maximum ΔG°⧧ value of 7.9 kcal/mol for the rate-determining C-C bond formation step. Our protocol has several advantages and can be further extended to one-pot sequential Knoevenagel condensation and Michael addition, and one-pot sequential Knoevenagel condensation and chemoselective reduction can be used for the synthesis of valuable precursors of pharmaceutical products under green and aqueous conditions.

Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single Atom Sites on Carbon Nitride for Selective Photooxidation of Methane into Methanol.

Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer-Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.

An efficient NiO/NiS/NiP heterostructure catalyst for oxygen evolution reaction

Hydrogen production through water splitting is crucial and hydrogen is considered a potential fuel for the future. To make water splitting commercially viable, inexpensive transition metal-based catalysts owing better efficiency and higher stability are needed. We have synthesized NiO, NiS, NiP, and their binary (NiO/NiS and NiS/NiP) and ternary (NiO/NiS/NiP) heterostructures catalysts. Synthesized catalysts have been analyzed through scanning electron microscopy, Fourier-transformed infrared, and X-ray diffraction spectroscopies for their structural characterization. The catalytic performance of all the synthesized catalysts has been evaluated towards oxygen evolution reaction (OER). The NiO/NiS/NiP heterostructure has been shortlisted as an efficient and stable electrocatalyst. The onset potential for OER has been found to be 1.49 V (vs. RHE) along with an overpotential of 262 mV @ 40 mA/cm2 current density and 60 mV dec-1, Tafel slope manifest the heterostructure as the best contender for OER compared to its counterparts (NiO, NiS and NiP) under similar water oxidation conditions. These results prove reported heterostructure is an efficient catalyst than nickel-based benchmark electrocatalysts. Moreover, controlled potential electrolysis has been performed for all electrocatalysts by chronoamperometry at 1.65 V (vs. RHE) and current density has been measured for an extended period of > 12 h which showed that most of the catalysts are stable enough.

Iron-doped catalyst synthesis in heterogeneous Fenton like process for dye degradation and removal: optimization using response surface methodology

Iron-doped hydrochar can effectively remove the methyl orange dye (MO). In this study, iron-doped hydrochar (5% Fe@BC) was successfully synthesized through a two-step hydrothermal carbonization (HTC) process, using FeSO4.7H2O and sawdust. It was subsequently employed for MO removal. The characterization of the synthesized Fenton-like catalyst (5% Fe@BC) was conducted, using scanning electron microscopy, Fourier-transform infrared and X-ray diffraction techniques to confirm the presence of iron species. The effects of different operating parameters such as catalyst mass, H2O2 concentration, solution pH, organic pollutant concentration, and reaction temperature have been examined. The Box-Behnken design combined with three factors: catalyst mass X1, temperature X2, organic pollutant concentration X3. The response surface methodology coupled with Box-Behnken Design was used to optimize the key variables and response. With this approach, an exhaustive assessment of the variables influencing the optimization process was performed. A significant quadratic model was generated through analysis of variance with a P-value of 0.0001 and an R2 of 0.99. This confirms a strong relationship between the variables and the response, as well as a high level of model predictability. The optimum conditions were achieved with a catalyst mass of 0.5 g/L, a temperature of 35.5 °C, and an MO concentration of 50 mg/L. The result indicates that 93% of the discoloration efficiency was achieved within 60 min under the optimal conditions. Iron doping in the (5% Fe@BC) plays a crucial role in the degradation and removal of MO. Therefore, the 5% Fe@BC prepared from sawdust and iron salts (FeSO4·7H2O) through a two-step HTC process is an inexpensive and effective catalyst for removing organic pollutant from aqueous solutions, using heterogeneous Fenton-like process.