Heterogeneous Iron Catalyst Research Articles

Iron hematite-magnetite composite supported on mesoporous SBA-15 synthesized by using silica from cogon grass as a solid catalyst in phenol hydroxylation

Phenol hydroxylation involves the oxidation of phenol (C6H5OH) using hydrogen peroxide (H2O2) to yield benzenediol (C6H4(OH)2), mainly catechol (CTL) and hydroquinone (HQ). These products are in high demand in the pharmaceuticals industry sector. Thus, it is still worth investigating for further improvement in terms of heterogeneous iron catalysts. Herein, this research focuses on an iron hematite (Fe2O3)-magnetite (Fe3O4) composite catalyst supported on SBA-15 using silica from cogon grass for phenol hydroxylation. The extracted silica exhibited a fine white powder appearance and an amorphous structure, used as a silica source for SBA-15 synthesis. After catalyst preparation, the presence of Fe2O3, Fe3O4, and Fe2O3-Fe3O4 composite on SBA-15 was confirmed by using X-ray absorption near-edge structure (XANES). X-ray photoelectron spectroscopy (XPS) analysis provided insights into the surface of the catalyst, revealing that Fe2O3-Fe3O4/SBA-15 had the highest dispersion of iron species. In terms of catalytic performance, Fe2O3-Fe3O4/SBA-15 displayed the highest conversion of 88 % and HQ selectivity of 46 % compared with lone Fe3O4/SBA-15 or Fe2O3 /SBA-15. The magnetic separation approach demonstrated the easy separation of catalysts containing Fe3O4. Reusability studies showed that Fe2O3-Fe3O4/SBA-15 maintained its activity up to the 4th cycle, suggesting minimized iron leaching compared to Fe3O4/SBA-15. Overall, this study provides insights into the catalytic performance of phenol hydroxylation and iron-based catalysts, emphasizing the potential of Fe2O3-Fe3O4/SBA-15 as an effective and reusable catalyst.

Sustainable Aerobic Allylic C-H Bond Oxidation with Heterogeneous Iron Catalyst.

Emerging techniques are revolutionizing the realm of chemical synthesis by introducing new avenues for C-H bond functionalization, which have been exploited for the synthesis of pharmaceuticals, natural compounds, and functional materials. Allylic C-H bond oxidation of alkenes serves as possibly the most employed C-H bond functionalization reaction. However, sustainable and selective approaches remain scarce, and the majority of the existing conditions still hinge on hazardous oxidants or costly metal catalysts. In this context, we introduce a heterogeneous iron catalyst that addresses the above-mentioned concerns by showcasing the aerobic oxidation of steroids, terpenes, and simple olefins to the corresponding enone products. This novel method provides a powerful tool for the arsenal of allylic C-H bond oxidation while minimizing the environmental concerns.

Tourmaline-mediated electrochemical system for sulfamethoxazole degradation: performance, mechanism, and toxicity evaluation

Antibiotics are emerging contaminants that have become a global concern because of their refractory and toxic characteristics. The treatment of antibiotic contaminants using advanced electrochemical oxidation processes is currently gaining interest. In this study, we constructed a natural iron-mediated electrochemical system for the removal of antibiotics using natural tourmaline (TM) as the heterogeneous iron catalyst, platinum (Pt) as the anode, and nickel foam (NiF) as the cathode. Sulfamethoxazole (SMX) was selected as the target antibiotic. The surface properties and components of TM were characterized using energy-dispersive X-ray spectroscopy, N2 adsorption–desorption isotherms, X-ray diffraction, and X-ray photoelectron spectroscopy. Compared with the Pt-NiF electrochemical system, the Pt-NiF-TM electrochemical system showed a 23 times enhanced reaction rate constant of SMX degradation under the optimal conditions of current density 4.17 mA/cm2, 200–400 mesh, TM dosage 3 g/L, and initial pH 3, in which SMX was almost completely degraded (removal rate = 99.92 %) after 60 min. The ·OH and ·O2– radicals generated in the Pt-NiF-TM electrochemical system were the active species for SMX degradation. Thirteen SMX degradation intermediates were identified and possible SMX degradation pathways were proposed. Density functional theory calculations demonstrated that C3 and N11 are the sites with higher electrophilic reactivity in SMX. Furthermore, toxicity calculations and analysis of SMX and its degradation products showed that after treatment with the Pt-NiF-TM electrochemical system, the toxicity of SMX to the microalgae Oocystis was reduced. Overall, this study provides a novel and environmentally friendly electrochemical system mediated by TM for the highly efficient degradation of antibiotic contaminants.

Heterogeneous iron catalyst for C(1)-H functionalization of 2-naphthols with primary aromatic alcohols.

An iron oxide nanocatalyst supported on a potassium exchanged zeolite-Y (Fe2O3-KY) is an efficient and reusable catalyst that promotes the selective α-H functionalization of 2-naphthols with various aromatic primary alcohols. The reaction occurs at 110 °C in dichloroethane and requires 6 h for completion. The product yields were found to vary with respect to the nature of the substituents. Benzyl alcohols with electron-donating groups gave the highest yields of up to 90%.

Pressurized electro-Fenton for the reduction of the environmental impact of antibiotics

This work evaluates the performance of a pressurized heterogeneous electro-Fenton (EF) process to transform the antibiotic into compounds that do not promote the appearance of bacteria resistant to antibiotic in the environment. Experimental system consisted of a pressurized non divided microfluidic electrochemical cell equipped with a jet aerator, flow-through electrodes and a fluidized bed of goethite as heterogeneous iron catalyst. Results show that meropenem (model antibiotic) can be degraded by EF and that the degradation rate depends on the gauge pressure applied: the higher is the pressurization, the faster is the abatement of meropenem. The antibiotic effect of the urine is related to meropenem remained in the treated urine, and the contribution of reaction intermediates does not seem to be relevant. The mineralization of the organic load is almost nil. The higher dissolved oxygen concentration of pressurized-EF and thus, the higher hydrogen peroxide generation seems to be the key point to explain the effect of pressure on EF process. Results confirm that moderated pressurized EF process (up to 3 bar) can be satisfactorily used to decrease the chemical risk of synthetic hospital urines, which opens the possibility of an optimized pre-treatment which may help to save cost in the treatment of these hazardous wastes.

Cover Feature: Precursor Nuclearity and Ligand Effects in Atomically‐Dispersed Heterogeneous Iron Catalysts for Alkyne Semi‐Hydrogenation (ChemCatChem 14/2021)

Cover Feature: Precursor Nuclearity and Ligand Effects in Atomically‐Dispersed Heterogeneous Iron Catalysts for Alkyne Semi‐Hydrogenation (ChemCatChem 14/2021)

Precursor Nuclearity and Ligand Effects in Atomically‐Dispersed Heterogeneous Iron Catalysts for Alkyne Semi‐Hydrogenation

AbstractNanostructuring earth‐abundant metals as single atoms or clusters of controlled size on suitable carriers opens new routes to develop high‐performing heterogeneous catalysts, but resolving speciation trends remains challenging. Here, we investigate the potential of low‐nuclearity iron catalysts in the continuous liquid‐phase semi‐hydrogenation of various alkynes. The activity depends on multiple factors, including the nuclearity and ligand sphere of the metal precursor and their evolution upon interaction with the mesoporous graphitic carbon nitride scaffold. Density functional theory predicts the favorable adsorption of the metal precursors on the scaffold without altering the nuclearity and preserving some ligands. Contrary to previous observations for palladium catalysts, single atoms of iron exhibit higher activity than larger clusters. Atomistic simulations suggest a central role of residual carbonyl species in permitting low‐energy paths over these isolated metal centers.

Metformin degradation in aqueous solutions by electro-activation of persulfate and hydrogen peroxide using natural and synthetic ferrous ion sources

In this study, the performances of natural (pyrite) and synthetic (nano-magnetite) heterogeneous iron catalysts as a source of ferrous ion on electro-activation of hydrogen peroxide (HP) and persulfate (PS) were compared for degradation of metformin (MET) as an emerging contaminant in aqueous solutions. The effects of catalyst type and dosage, oxidant type and dosage, applied current (10–50 mA), drug concentration (15–80 mg/L), and time on MET removal were evaluated. The removal capacity of the processes was determined by evaluating the stoichiometry ratio of MET: oxidant. The process mechanism study showed that hydroxyl radical and sulfate radical were the main responsible for MET degradation in the HP-activating and PS-activating systems, respectively. The synergy between various mechanisms including adsorption, electrochemical precipitation, oxidation, and electrocoagulation was more prominent in nano-magnetite systems. A comparative study of oxidants function showed that although PS was more effective, it was more dependent on the presence of activators to remove MET. The results suggested that there was a positive correlation between the catalysts ability to distribute Fe2+ and mineralization rate. However, the highest removal efficiency of MET (89.25%) and TOC (68.42%) belonged to the natural catalyst (pyrite/PS), while lower energy demand (1.43 Wh/L), higher removal capacity, and more stability were observed in the synthetic catalyst.

Cover Feature: Iron Coordination to Hollow Microporous Metal‐Free Disalphen Networks: Heterogeneous Iron Catalysts for CO2 Fixation to Cyclic Carbonates (Chem. Eur. J. 4/2020)

Cover Feature: Iron Coordination to Hollow Microporous Metal‐Free Disalphen Networks: Heterogeneous Iron Catalysts for CO₂ Fixation to Cyclic Carbonates (Chem. Eur. J. 4/2020)

Iron Coordination to Hollow Microporous Metal-Free Disalphen Networks: Heterogeneous Iron Catalysts for CO2 Fixation to Cyclic Carbonates.

This work shows that a hollow and microporous metal-free N,N'-phenylenebis(salicylideneimine) (salphen) network (H-MSN) can be engineered by Sonogashira coupling of [tetraiodo{di(Zn-salphen)}] building blocks with 1,4-diethynylbenzene in the presence of silica templates and by successive Zn and silica etching. Iron(III) ions could be incorporated into the H-MSN to form hollow and microporous Fe-disalphen networks (H-MFeSN) with enhanced microporosity and surface area. The H-MFeSN showed efficient catalytic performance and recyclability in the CO2 conversion to cyclic carbonates.

Kinetics of wet air oxidation of sodium sulfide over heterogeneous iron catalyst

AbstractWet air oxidation (WAO) is an established technique for reducing the chemical oxygen demand (COD) of refinery sulfidic spent caustic waste. In the present work, the heterogeneous form of the cheap and abundant catalyst ferrous sulfate (FeSO4) was employed for WAO of sodium sulfide. The performance of this catalyst in the oxidative destruction of this model compound is thus far unfamiliar. Kinetic data for the non‐catalytic and catalytic oxidation processes was collected in a batch reactor. For the catalytic process, temperature (T), oxygen partial pressure () and catalyst concentration (ω) were varied in the ranges 80‐150°C, 0.69‐2.06 MPa and 0.8‐2.4 g/L respectively. Around 94% COD was destroyed within 1 h when feed containing 8 g/L of sulfide was oxidized at T = 100°C, = 0.69 MPa, and ω = 0.8 g/L. First, the data on disappearance of COD were fitted to a power law model and reaction rate constants were determined. The activation energy for the non‐catalytic (91 kJ/mol) and catalytic (50 kJ/mol) oxidation process was found from the temperature dependence of the rate constants. Second, hyperbolic models based on Langmuir‐Hinshelwood (L‐H) and Eley‐Rideal (E‐L) kinetics were used for fitting kinetic data. It was found that the L‐H model suggesting dissociative adsorption of oxygen provided the best fit. In this way, a deep insight into oxidation kinetics of sodium sulfide was provided.

Activation of persulfate by homogeneous and heterogeneous iron catalyst to degrade chlortetracycline in aqueous solution

This study investigates the removal of chlortetracycline (CTC) antibiotic using sulfate radical-based oxidation process. Sodium persulfate (PS) was used as a source to generate sulfate radicals by homogeneous (Fe2+) and heterogeneous (zero valent iron, ZVI) iron as a catalyst. Increased EDTA concentration was used to break the CTC-Fe metal complexes during CTC estimation. The influence of various parameters, such as PS concentration, iron (Fe2+ and ZVI) concentration, PS/iron molar ratio, and pH were studied and optimum conditions were reported. CTC removal was increased with increasing concentration of PS and iron at an equal molar ratio of PS/Fe2+ and PS/ZVI processes. PS/Fe2+ and PS/ZVI oxidation processes at 1:2 (500 μM PS and 1000 μM) molar ratio showed 76% and 94% of 1 μM CTC removal in 2 h. Further increased molar ratio 1:2 onwards, PS/Fe2+ process showed a slight increase in CTC degradation whereas in PS/ZVI process showed similar degradation to 1:2 (PS/Fe) ratio at constant PS 500 μM concentration. Slower activation of persulfate which indirectly indicates the slower generation of sulfate radicals in PS/ZVI process showed higher degradation efficiency of CTC. The detected transformation products and their estrogenicity results stated that sulfate radicals seem to be efficient in forming stable and non-toxic end products.

Facile synthesis of highly reactive and stable Fe-doped g-C3N4 composites for peroxymonosulfate activation: A novel nonradical oxidation process

Ferrous ions (Fe2+) are environmentally friendly materials but show extremely inefficient persulfate activation. Polymeric graphitic carbon nitride (g-C3N4) has recently shown potential to activate persulfates, but the process requires intense light irradiation. To overcome these drawbacks, we designed an innovative heterogeneous iron catalyst by doping Fe into g-C3N4 (Fe-g-C3N4) and used it to activate peroxymonosulfate (PMS) for degradation of pollutant phenol. The catalysts synthesized were fully characterized with various techniques, such as X-ray diffraction, Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. Fe was found to be coordinated with the framework of g-C3N4. Approximately 100% degradation of phenol was achieved with Fe-g-C3N4 after 20 min of reaction, whereas less than 5% degradation of phenol was achieved with Fe2+. Fe-g-C3N4-PMS had a wide effective pH range, and its reactivity was nearly independent of natural illumination. In contrast to the previously proposed radical mechanisms, quenching experiments revealed that nonradical oxidation contributed to the observed degradation. The OO bond in the activated PMS likely underwent heterolysis, producing high-valence iron species (FeIVO) as the primary active species. These findings have important implications for the development of a selective heterogeneous nonradical-oxidation process.

Selective reductive cleavage of C[sbnd]O bond in lignin model compounds over nitrogen-doped carbon-supported iron catalysts

Lignin has recently attracted much attention as a promising resource to produce fuels and aromatic chemicals. The selective cleavage of CO bond while preserving the aromatic nature has become one of the major challenges in the catalytic valorization of lignin to aromatic chemicals. In this work, we report that the selective reductive cleavage of CO bond in lignin model compounds can be successfully achieved through heterogeneous iron catalysis. The hydrogenolysis of α-O-4 model linkage shows that the iron catalyst prepared by the simultaneous pyrolysis of iron acetate and 1,10-phenanthroline on activated carbon at 800 °C is the most active iron catalyst, affording phenol and toluene with yields of 95% and 90%, respectively. This aromatics selectivity is found to be much higher than that obtained over noble metal catalysts. The presence of N⋯Fe species as the active center of heterogeneous iron catalyst was confirmed by various technologies especially XPS and H2-TPR. For the β-O-4 model linkage, the vicinal OH group was essential for the iron-catalyzed hydrogenolysis of ether linkage. The oxidation of the α-carbon in the β-O-4 model compounds can significantly decrease the bond dissociation energy of ether linkage, giving depolymerization products in moderate to excellent yields.

Heterogeneous Iron Catalyst for Aerobic Oxi-dation of Alcohols and Benzylic Compounds

Key words core–shell catalyst - iron catalysis - oxidation - alcohols - benzylic compounds

Graphitic Carbon Nitride (g‐C3N4)‐derived Fe‐N‐C Catalysts for Selective Hydrodeoxygenation of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran

AbstractAs Fe is more abundant and economic than Cu and Ni, it is probably a more attractive non‐noble alternative to precious metals in biomass conversions, for which usually require promising catalysts for large‐scale production. In this work, economic and environmental benign heterogeneous iron catalysts prepared by simultaneous pyrolysis of graphitic carbon nitride and iron precursors on activated carbon, were demonstrated to be active for the hydrodeoxygenation of biomass‐derived 5‐hydroxymethylfurfural to 2,5‐dimethylfuran. The effect of pyrolysis temperature, support, iron content, the type of g‐C3N4 and iron precursor, and N/Fe ratio were explored thoroughly, and reaction parameters such reaction temperature and H2 pressure were also investigated. The highest DMF yield of 85.7 % was obtained at 240 °C for 3 h, which is comparable to that obtained over iron catalysts prepared from precious iron complexes. The investigation of reaction pathway showed that 5‐methylfurfural was the possible intermediate. The stability of as‐prepared Fe‐N‐C catalyst could be improved after treatment with aqueous HCl solution.

Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Heterogeneous Iron Catalysts.

This work provided the first example of selective hydrodeoxygenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) over heterogeneous Fe catalysts. A catalyst prepared by the pyrolysis of an Fe-phenanthroline complex on activated carbon at 800 °C was demonstrated to be the most active heterogeneous Fe catalyst. Under the optimal reaction conditions, complete conversion of HMF was achieved with 86.2 % selectivity to DMF. The reaction pathway was investigated thoroughly, and the hydrogenation of the C=O bond in HMF was demonstrated to be the rate-determining step during the hydrodeoxygenation, which could be accelerated greatly by using alcohol solvents as additional H-donors. The excellent stability of the Fe catalyst, which was probably a result of the well-preserved active species and the pore structure of the Fe catalyst in the presence of H2 , was demonstrated in batch and continuous flow fixed-bed reactors.

A Sustainable Heterogeneous Iron Catalyst Fe/SBA‐15 towards Direct Arylation of Unactivated C(sp3)−H and C(sp2)−H Bonds with Arenes

AbstractIron grafted over mesoporous silica (8 wt %Fe/SBA‐15) is a sustainable, efficient heterogeneous iron catalyst for direct arylation of biphenyl methane C(sp3)−H and benzene C(sp2)−H bonds. The selective extraction deposition (SED) technique was adopted to graft iron easily over the mesoporous support SBA‐15 by using LaFeO3 as an iron precursor. The synthesized catalyst has been characterized by EPR spectroscopy, diffuse reflectance UV/Vis spectroscopy, and temperature programmed reduction (TPR) analysis to understand the coordination environment and state of oxidic iron species grafted over the mesoporous SBA‐15. TPR results confirm the presence of isolated, clustered, oligomeric oxidic iron species in the catalyst. The adopted SED technique is highly successful for grafting 8 wt % iron into the mesopores of SBA‐15 without forming iron oxide particles. Unlike homogeneous iron, the 8 wt %Fe/SBA‐15 catalyst does not need support from an electron‐withdrawing group and additives to carry out arylation of benzene and could be successfully recycled five times.

ChemInform Abstract: Sustainable Iron‐Catalyzed Direct Imine Formation by Acceptorless Dehydrogenative Coupling of Alcohols with Amines.

The Acceptorless Dehydrogenative Coupling (ADC) of alcohols with amines is reported using a heterogeneous Fe-catalyst. The reaction operates under mild conditions with the liberation of dihydrogen and water as the byproducts. The developed ADC strategy is simple, efficient, exhibits wide functional group tolerance and can be scaled up. The present catalytic approach possesses a dual role; acting as a catalyst as well as being magnetically separable. The sustainable reuse of a heterogeneous iron catalyst is also shown.

Synthesis, characterization and activity of homogeneous and heterogeneous (SiO2, NaY, MCM-41) iron(III) catalysts on cyclohexane and cyclohexene oxidation

This work deals with the synthesis and characterization of two homogeneous and three heterogeneous iron(III) catalysts, which were evaluated in the oxidation of cyclohexane and cyclohexene, using H2O2 as oxidant. The homogeneous catalyst [Fe2(BPA)2(μ-OCH3)2(Cl)2], (1), where BPA is the deprotonated form of N-(2-hydroxybenzyl)-N-(pyridin-2-ylmethyl) amine, is a dinuclear iron(III) compound, as determined by X-ray diffraction studies. Compound [FeIII(HBPCℓNOL)(Cl)2], (2), where HBPCℓNOL is N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)(3-chloro)(2-hydroxy) propylamine, is a mononuclear iron(III) compound. The reaction of the ligand HBPA with the 3-glycidoxypropyltrimethoxysilane molecule followed by the reaction with different inorganic matrices (silica-gel, NaY zeolite, MCM-41) resulted in the organo functionalized solids SiL, NaYL and MCM-41L, respectively. These materials were reacted with iron(III) salt, affording the heterogeneous catalysts SiLFe, NaYLFe and MCM-41LFe, respectively. They were characterized by elemental analyses, HR-CS AAS, solid state MAS NMR (29Si, 13C), IR, UV–vis, TGA, Mossbauer, and textural analyses. The major product formed in all the oxidation reactions was the hydroperoxide derivative. When cyclohexane was the substrate, the homogeneous catalysts were more efficient than the heterogeneous ones. In contrast, the heterogeneous systems showed better results with cyclohexene than with cyclohexane, reaching about 30% in the presence of NaYLFe.