Recyclable Catalyst Research Articles

Croton macrostachyus leaf-mediated biosynthesis of copper oxide nanoparticles for enhanced catalytic reduction of organic dyes

Introduction. Owing to the increasing use of organic dyes, the biosynthesis of metal oxide nanocatalysts is urgently needed as an economical and environmentally friendly solution to reduce their waste release. Method. In this study, we synthesized copper oxide nanoparticles (CuO NPs) by the sol–gel method using Croton macrostachyus leaf extracts as capping and reducing agents. The biosynthesized CuO catalysts were characterized using x-ray diffraction analysis (XRD), thermogravimetric differential thermal analysis (TGA-DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). Result. The result showed that the synthesized CuO NPs had a crystallite size of about 9 nm and had good crystalline texture. Furthermore, the catalyst showed the best catalytic reduction performance in 1 min for methylene blue (MB) and 3 min for methyl orange (MO). Furthermore, the CuO catalyst synthesized using Croton macrostachyus leaf extract resulted in apparent rate constant (Kapp) values for MB and MO of 0.06793 s−1 and 0.01877 s−1, respectively. Discussion. The recyclability of the CuO catalyst was investigated, and it was shown that the catalysts are suitable for reuse in dye reduction. Therefore, the catalytic activity of this study suggests that the CuO nanocatalysts prepared in this work are a potential candidate for controlling organic pollutants or trace amounts of naturally occurring active organic chemicals in all environmental dye wastes.

Organocatalytic Synthesis of (Hetero)arylidene Malononitriles Using a More Sustainable, Greener, and Scalable Strategy.

The establishment of a green and sustainable Knoevenagel condensation reaction in organic chemistry is still crucial. This work aimed to provide a newly developed metal-free and halogen-free catalytic methodology for the synthesis of CS and (hetero-) arylidene malononitriles in the laboratory and industrial scale. The Knoevenagel condensation reaction of various carbonyl groups with malononitrile was investigated in ethanol, an ecofriendly medium, in the presence of seven nitrogen-based organocatalysts. A comparative study was conducted using two as-obtained and four commercially available nitrogen-based organocatalysts in Knoevenagel condensation reactions. The synthesis of CS gas (2-chlorobenzylidene malononitrile) using a closed catalytic system was optimized based on their efficiency and greener approach. The conversion of 100% and excellent yields were obtained in a short time. The products could be crystallized directly from the reaction mixture. After separating pure products, the residue solution was employed directly in the next run without any concentration, activation, purification, or separation. Furthermore, the synthesis of 2-chlorobenzylidenemahmonitrile (CS) was carried out on a large scale using imidazole as a selected nitrogen-based catalyst, afforded crystalline products with 95 ± 2% yield in five consecutive runs. Energy efficiency, cost saving, greener conditions, using only 5 mol% of organocatalyst, high recyclability of catalyst, prevention of waste, recycling extractant by a rotary evaporator for non-crystallized products, demonstrated the potential commercial production of CS using imidazole in ethanol as an efficient and highly recyclable catalytic system.

N-Formylation of Carbon Dioxide and Amines with EDTA as a Recyclable Catalyst under Ambient Conditions

The reduction of CO2 is an important method to produce chemicals such as methanol, formic acid, formaldehyde, etc. In general, the reduction of CO2 is carried out at high temperatures and pressures with precious metals as catalysts, which is not favorable for industrial procedures. Thus, it will be very useful if researchers can find cost-effective catalysts for industrial application in CO2 reduction. In this work, commercially available ethylenediaminetetraacetic acid (EDTA) was tested as a cheap, non-toxic, and recyclable catalyst to initiate the N-carbonylation reaction of CO2 with amines. After screening various reaction parameters, including temperature, pressure, time, solvent, and reducing agent, the optimal reaction conditions were obtained: 80 °C, 2 MPa, 6 h, 50 mmol% catalyst dosage, 1 mL DMSO, and 1:1 molar ratio of amine to reducing agent. Notably, further studies confirmed that EDTA could also be effective for N-formylation even under ambient conditions (0.1 MPa and room temperature). The suitability of the catalyst for 26 kinds of substrates (including aliphatic amines, aromatic amines, and alicyclic amines) and its reusability were also investigated, with satisfactory results. Scale-up research has been performed effectively with a high conversion of amine (83%) to obtain the mono-formylated product selectively. Finally, the mechanism of the reaction between amine and CO2 has been proposed via control experiments and compared with results in the literature.

Poly(2,2'-Bibenzimidazole)-Supported Iridium Complex: A Recyclable Metal-Polymer Ligand Bifunctional Catalyst for the N-Methylation of Amines with Methanol.

The design and development of new types of catalysts is one of the most important topics for modern chemistry. Herein, a polymer-supported iridium complex Cp*Ir@Poly(2,2'-BiBzIm) was designed and synthesized by the coordinative immobilization of [Cp*IrCl2]2 on 2,2'-bibenzimidazoles. In the presence of the catalyst (0.5 mol % Ir) and Cs2CO3 (0.3 equiv), a variety of N-methylated amines were obtained in high yields with complete selectivity. More importantly, the catalyst could be recycled without an obvious loss of activity for six cycles. Apparently, the designed catalyst combines the advantages of both homogeneous and heterogeneous catalysis.

Synthesis and crystal structure of new Mn (III) complex; a target catalyst for direct conversion of thiols after heterogenization

In this study, we are interested in the synthesizing of a new water-soluble complex of Mn (III) formulated as [Mn(pzo)(dipic)(H2O)2]2·3H2O; hereafter referred to as complex 1 where pzo− = pyrazonate and dipic2− = pyridine-2,6-dicarboxylate, under hydrothermal conditions. The molecular structure of complex 1 is primarily determined by single crystal X-ray diffraction (SC-XRD) which shows two mono-nuclear complexes of Mn (III) with three lattice water molecules. According to SC-XRD, complex 1 crystallizes in space group P1¯ of a triclinic system. The center of Mn (III) is seven-coordinated with a distorted pentagonal-bipyramidal geometry with three oxygen atoms and two nitrogen atoms in the equatorial plane. Two oxygen atoms of two water molecules are coordinated in the axial positions. In addition, the structure of complex 1 has been studied by elemental analysis (CHN), Fourier-transform infrared spectroscopy (FT-IR (, thermogravimetric analysis/differential thermal analysis/differential thermogravimetry (TGA/DTA/DTG). Complex 1 has been immobilized on the silica-coated Fe3O4 nanoparticles to produce an efficient and recyclable heterogeneous catalyst formulated as Fe3O4@SiO2@1; hereafter referred to as catalyst 1. Catalyst 1 was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), energy-dispersive X-ray spectrometer (EDS), FT-IR, scanning electron micrograph (SEM), powder X-ray diffraction pattern (PXRD), and Brunner-Emmet-Teller (BET). 1 was used as a new heterogeneous catalyst for the oxidative coupling of thiols to their corresponding disulfides using 30 % H2O2. Under optimum reaction conditions, catalyst 1 exhibited high catalytic activity. 1 can be recovered by a magnet and reused for at least 7 consecutive cycles without significant loss of catalytic performance.

In-situ Cu mesh growth of reusable OVs-WO3/CuO heterojunction photocatalysts for enhanced nitrogen fixation efficiency

The loaded photocatalyst is an ideal material for nitrogen fixation, which does not have the problem of secondary pollution caused by powdered catalysts, and has the advantages of uniform distribution, high efficiency and easy recovery. In this paper, CuO and WO3 were grown on copper mesh (CM) by in-situ etching and solvothermal method. The photogenerated carriers and light absorption properties were synergistically promoted with the help of oxygen vacancies and S-type heterojunctions. Under simulated visible-light conditions, a liquid-membrane type reaction was employed and the nitrogen fixation performance was significantly improved. The optimal ammonia production rate of WO3/CuO/CM was 3.878 × 10−2 μmol/cm2/h, which was 9.37 and 5.16 times higher than WO3/CM and CuO/CM, respectively. This study provides ideas for the design of recyclable heterojunction catalysts with oxygen vacancies.

Controllable Assemblies of Au NPs/P5A for Enhanced Catalytic Reduction of 4-Nitrophenol.

Efficient catalytic reduction of 4-nitrophenol (4-NP) is one focus of industry and practical engineering, because 4-NP is one of the most important sources of pollution of the ecological environment and human health. Here, coassembled hybrid composites of pillar[5]arene (P5A) and gold nanoparticles (Au NPs) were successfully developed by a one-step synthetic method as a type of water-insoluble catalyst for the reduction of 4-NP. The geometric and topological structures, as well as physiochemical properties of Au NPs/P5A composite catalyst, were fully characterized and analyzed through various tests such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), indicating that Au NPs were well dispersed on the surface of the two-dimensional film of assembled P5A. The influence factors of the catalytic reduction of 4-NP were further investigated and discussed, confirming that the content of Au NPs and the concentration of 4-NP were very significant during the catalysis. The catalytic reaction was carried out at the catalyst concentration of 100 mg·L-1 and an initial 4-NP concentration of 90 mg·L-1 under 30 °C. The calculated reaction rate constant was 0.3959 min-1 and the reduction rate of 4-NP was more than 95% in 20 min. In addition, the as-prepared catalyst can maintain a high catalytic efficiency after five cycles. Thus, the easily recyclable composite catalyst with poor aqueous solution can exhibit prospective application to the treatment of 4-NP in water.

Carboxymethyl Cellulose (CMC) as a Recyclable and Biodegradable Catalyst: A Greener Solvent-free Preparation of Pyrano[2,3-d]pyrimidines

Carboxymethyl Cellulose (CMC) as a Recyclable and Biodegradable Catalyst: A Greener Solvent-free Preparation of Pyrano[2,3-d]pyrimidines

G‐C3N4 Photocatalyzed Decarboxylative Oxidation of Carboxylic Acids and the Oxidation of Alkenes and Alkanes

AbstractThe decarboxylative oxygenation of readily available carboxylic acids as well as the oxidation of alkenes and alkanes has been accomplished through visible light using g‐C3N4 as a robust and recyclable catalyst. The scalable protocol furnishes an array of aldehydes and ketones under mild reaction conditions, requiring only molecular oxygen as an oxidant. Notably, no addition of stochiometric amounts of base is required, and furthermore, the reaction proceeds efficiently open to the air.

Modulating Cu2O/CuO on attapulgite for boosting peroxymonosulfate activation

Peroxymonosulfate (PMS) activation is an economically viable and efficient advanced oxidation process used to degrade recalcitrant organic pollutants. In this study, the copper oxide/attapulgite (CuxO/ATP) catalyst was synthesized via the hydrothermal method. The catalytic degradation efficiency was assessed using ciprofloxacin (CIP) as the model pollutant. The influence of catalyst dosage and PMS concentration on CIP degradation was examined. Additionally, the capability of the catalyst to degrade CIP under varying pH conditions, temperatures, and in the presence of diverse inorganic ions was investigated. The findings revealed that CuxO/ATP exhibited superior performance compared to pure CuxO in PMS activation for CIP degradation. Microstructural analysis indicated well-dispersed CuxO nanoflowers on the attapulgite, facilitating a synergistic effect between the two components. The presence of attapulgite enhanced the dispersion of CuxO, leading to an increase in the exposed surface area. In addition, attapulgite facilitated the adsorption of pollutants onto the CuxO interface, while CuxO, in turn, activated PMS to generate active free radicals, thereby enabling the catalytic oxidation of pollutants. Through a series of free radical quenching experiments, sulfate radicals were identified as the predominant species responsible for CIP degradation, playing a pivotal role in the system. Moreover, a plausible catalytic mechanism was discussed. Furthermore, reusability tests demonstrated the catalyst's stability and recyclability. This research not only presents a novel and robust approach for CuxO catalyst synthesis but also offers deeper insights into the mechanism underlying CuxO activation of PMS.

A Recyclable Inorganic Lanthanide Cluster Catalyst for Chemoselective Aerobic Oxidation of Thiols.

Optimizing lanthanide catalyst performance with organic ligands often encounters significant challenges, including susceptibility to water or oxygen and complex synthesis pathways. To address these issues, our research focuses on developing inorganic lanthanide clusters with enhanced stability and functionality. In this study, we introduce the [Sm6O(OH)8(H2O)24]I8(H2O)8 cluster (Sm-OC) as a sustainable and efficient catalyst for the aerobic oxidation of thiols under heating conditions. The Sm-OC catalyst demonstrated remarkable stability, outstanding recyclability, and excellent chemoselectivity across a diverse range of functional groups in 38 different tests. Notably, it enables efficient unsymmetrical disulfide synthesis and prevents the formation of over-oxidized by-products, highlighting its superior performance. This Sm-OC catalyst provides a practical and robust tool for the precise construction of versatile disulfides, thus establishing a template for the broader use of lanthanide clusters in organic synthesis.

A new DES-mediated synthesis of Henna-based benzopyranophenazines and benzoxanthenetriones

MTPPBr/THFTCA-DES was prepared as a new deep eutectic solvent (DES) from a mixture (molar ratio 7:3) of methyltriphenyl-phosphonium bromide (MTPPBr) and tetrahydrofuran-2,3,4,5-tetra-carboxylic acid (THFTCA), and characterized with various spectroscopic techniques, densitometer, and eutectic point. Then, it was used as a new and powerful catalyst for the synthesis of two sets of biologically important compounds, namely the Henna-based benzopyranophenazines and benzoxan-thenetriones. Solvent-free conditions, short reaction time, high efficiency, and easy recycling and separation of the DES catalyst are among the most important features of the presented method. Also, there is a nice consistency between the proposed structure of the DES compound, the integration values of the 1H NMR peaks, and the ratio of MTPPBr to THFTCA obtained from the eutectic point phase diagram. In addition, the reduction of peak splitting patterns in DES compared to the two primary materials can be good evidence of the formation of hydrogen bonds between the two components.

Ru/GCN Nanocomposite as an Efficient Catalyst for Hydrogen Generation from Sodium Hypophosphite.

Sodium hypophosphite is a promising green source for generating clean elemental hydrogen without pollutants. This study presents the development of an efficient heterogeneous catalyst, Ru/g-C3N4 (Ru/GCN), for hydrogen generation from sodium hypophosphite. The Ru/GCN catalyst demonstrates excellent activity under mild reaction conditions and maintains its effectiveness over multiple cycles without significant loss of activity. This easily separable and recyclable heterogeneous catalyst is straightforward to operate, non-toxic, eco-friendly, and provides a cost-effective alternative to the extensive use of expensive noble metals, which have limited industrial applications. The Ru/GCN catalyst was characterized using various material characterization and spectral methods, including powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). Hypophosphite, combined with the catalytically active and recyclable Ru/GCN catalyst, forms a system with high potential for industrial-scale hydrogen production, suggesting promising avenues for further research and application.

Carboxymethyl Cellulose as a Recyclable and Biodegradable Heterogeneous Catalyst for Convenient Synthesis of 2-Amino-4H-chromenes

Carboxymethyl Cellulose as a Recyclable and Biodegradable Heterogeneous Catalyst for Convenient Synthesis of 2-Amino-4H-chromenes

Water-Dispersible, Magnetically Recyclable Heterogeneous Cobalt Catalyst for C-C and C-N Cross-Coupling Reactions in Aqueous Media.

A cobalt catalyst supported on an iron oxide core, denoted as γ-Fe2O3@PEG@THMAM-Co, has been prepared and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray mapping, thermogravimetry differential thermogravimetry, vibrating sample magnetometry, and inductively coupled plasma. Polyhydroxy end groups in the shell make the catalyst particles dispersible in water, allowing Hiyama, Suzuki, and C-N cross-coupling reactions of aryl iodides and bromides. The catalyst could be recovered by magnetic decantation and reused for at least five successive runs with a negligent decrease in its activity or changes in its morphology. Water as a solvent without requiring additives, surfactants, or organic co-solvents, as well as an abundant and low-cost cobalt catalyst combined with facile recovery, low leaching, and scalability, provides an environmentally and economically attractive alternative to established palladium-catalyzed C-C and C-N coupling reactions.

Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids.

A series of acylhydrazone-based N,N-chelate half-sandwich iridium complexes have been synthesized through a facile route in good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished catalyzed by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half-sandwich iridium catalyst system exhibited high catalytic activity and stability, and a high TOF of 316.7 h-1 could be achieved with a catalyst loading as low as 0.05 mol %. Furthermore, the sustainable catalyst could be reused at least five times without obviously losing its activity, highlighting its potential application in industry. Molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.

Ca-doped ZnO nanoparticles for MB dye degradation and adsorptive removal of tinidazole.

Industrial dye degradation involves several processes by which dyes are broken down, ideally into innocuous products. Methylene blue (MB) is one of the most commonly employed dyes in the textile industry and is released into water in routine industry processes. These discharges lead to creating a nocuous nature for humans and animals. Drugs are also discharged into water bodies from various pharmaceutical industries. In these two contexts, in the present work, the green synthesis of calcium-doped zinc oxide nanoparticles (Ca-doped ZnO NPs) is achieved using the aqueous peel extract of Citrus limetta by the solution combustion technique. The structural, morphological, and optical properties of the synthesized Ca-doped ZnO NPs are investigated using XRD, FTIR, SEM, EDX, and UV-visible spectroscopy. The prepared NPs were subjected to photocatalytic degradation of MB dye under visible-light illumination, which shows ~ 95% dye degradation. The synthesized Ca-doped ZnO NPs were also employed to adsorb tinidazole (TDZ), a nitroimidazole antibiotic, from water samples. An excellent adsorptive capacity of the NPs was observed for selectively adsorbing the TDZ ~ 96.2%. The drug TDZ was found to have pseudo-second-order kinetics. The catalyst recycling proved its repeatability; removal of the dye reached up to 92% after three successive usages. Therefore, using waste Citrus limetta peel extract, the multifunctional Ca-doped ZnO NPs were synthesized, which maintained effective adsorption potential and photocatalytic abilities and could be used as an effective material for environmental remediation.

Atomically dispersed Rh catalysts formed on defective CeO2 surfaces with hydroformylation activity

The electron density of the metal active sites depends on the surface properties of the support. This study aimed to demonstrate that the formation of atomically dispersed Rh on ceria and the corresponding Rh electron density can be tuned depending on ceria concentration. The highly optimized Rh/CeO2-Al2O3 catalyst exhibited the highest activity during propylene hydroformylation, which was similar to that of the commercially available homogeneous catalyst RhCl(PPh3)3. Combined analytical results and theoretical calculations demonstrated that the increased Ce3+ fraction promoted high Rh electron density and attenuated CO adsorption strength, resulting in an increased hydroformylation activity. Additionally, the catalyst achieved separation and high added value by converting olefins to aldehydes through hydroformylation of olefins in a mixed C2–C4 olefin/paraffin gas. This study showed that atomically dispersed metal supported catalysts can be designed as recyclable heterogeneous catalysts by tailoring the local environment and corresponding electron density of the metal to achieve high activity similar to that of the homogeneous catalysts that manipulate ligands around the metal.

Iridium complex immobilized on covalent triazine framework derived from biomass as a recyclable catalyst for the dehydrogenation of formic acid

The first example of covalent triazine frameworks derived from biomass was designed and synthesized. Furthermore, an iridium complex Cp*Ir@CTF-biomass was prepared by the coordinative immobilization of [Cp*IrCl2]2 on the synthesized covalent triazine framework. In the presence of Cp*Ir@CTF-biomass (0.03 mol % Ir), the reaction was carried out for 24 min at 80 °C and an almost complete dehydrogenation of formic acid with an initial TOF of 7627 h−1 was observed. Further experiments confirmed that heterogeneous catalyst Cp*Ir@CTF-biomass and its homogeneous analog [Cp*Ir(pyridine)Cl2] have approximate catalytic activity. Moreover, catalytic activity of Cp*Ir@CTF-biomass is well maintained during six runs.©2024 Elsevier Inc. All rights reserved.

Oxidative Cleavage of α-O-4, β-O-4, and 4-O-5 Linkages in Lignin Model Compounds Over P, N Co-Doped Carbon Catalyst: A Metal-Free Approach.

Developing efficient metal-free catalysts for lignin valorization is essential but challenging. In this study, a cost-effective strategy is employed to synthesize a P, N co-doped carbon catalyst through hydrothermal and carbonization processes. This catalyst effectively cleaved α-O-4, β-O-4, and 4-O-5 lignin linkages, as demonstrated with model compounds. Various catalysts were prepared at different carbonization temperatures and thoroughly characterized using techniques such as XRD, RAMAN, FTIR, XPS, NH3-TPD, and HRTEM. Attributed to higher acidity, the P5NC-500 catalyst exhibited the best catalytic activity, employing H2O2 as the oxidant in water. Additionally, this metal-free technique efficiently converted simulated lignin bio-oil, containing all three linkages, into valuable monomers. Density Functional Theory calculations provided insight into the reaction mechanism, suggesting substrate and oxidant activation by P-O-H sites in the P5NC-500, and by N-C-O-H in the CN catalyst. Moreover, the catalyst's recyclability and water utilization enhance its environmental compatibility, offering a highly sustainable approach to lignin valorization with potential applications in various industries.