Heterogeneous Fenton-type Catalysts Research Articles

Valorization of alkaline lignin and optimization of vanillin production by heterogeneous Fenton-type catalysts

Fenton processes are a promising approach toward high-value chemical production from waste lignin. In this study, heterogeneous Fenton oxidation was employed to convert alkaline lignin into vanillin. The effects of Fe0, Fe2+, Fe3+, and H2O2 concentrations, temperature (25–50 °C), and reaction time (15–60 min) on vanillin production from lignin was investigated using response surface methodology under a three-level factorial design. The study reveals that the concentrations of Fe0, Fe2+, Fe3+, and H2O2 had an important effect on vanillin yield, whereas reaction temperature and time had positive effects on the process of vanillin production. Based on the numerical optimization and desirability function, the optimum conditions were 38.05 mg/L Fe0, 49.45 mg/L Fe2+, 71.35 mg/L Fe3+, and 1884.4 ppm H2O2 at 41.404 °C for 60 min at pH 3. Under these conditions, the vanillin yield obtained was 0.690%, which was increased by 2.59-fold from lignin. The experimental results agreed with the predicted values. We show that heterogeneous Fenton oxidation has the potential to convert lignin into high-value aromatic compounds when carried out under optimum conditions.

Catalytic Properties of Phosphate-Coated CuFe2O4 Nanoparticles for Phenol Degradation

Copper ferrite (CuFe2O4) nanoparticles were prepared using the sol-gel autocombustion method and then coated with phosphate using different treatments with H3PO4. The structural and chemical properties of the phosphate-coated CuFe2O4 nanoparticles were controlled by changing the concentration of H3PO4 during the coating process. The prepared nanoparticles were characterized using XRD, FTIR, SEM, and EDS which provided information about the catalysts’ structure, chemical composition, purity, and morphology. The catalytic and photocatalytic activities of the phosphate-coated CuFe2O4 samples were tested and evaluated for the degradation of phenol using HPLC. The prepared nanoparticles successfully emerged as excellent heterogeneous Fenton-type catalysts for phenol degradation. The phosphate-coated CuFe2O4 catalysts exhibited a higher catalytic activity compared with the uncoated CuFe2O4 ones. Such a higher catalytic performance can be attributed to enhanced morphological, electronic, and chemical properties of the phosphate-coated CuFe2O4 nanoparticles. Additionally, the phosphate-coated CuFe2O4 nanoparticles also revealed a higher catalytic activity compared with TiO2 nanoparticles. Different experimental conditions were investigated, and complete removal of phenol was achieved under specific conditions.

Oxidative degradation of sulfanilamide catalyzed by Fe/Cu/Al-pillared clays

An oxidative degradation of an antibiotic sulfanilamide with hydrogen peroxide was carried out in the presence of Fe/Cu/Al-pillared clays as heterogeneous Fenton type catalysts. Fe/Cu/Al-pillared clays were synthesized by intercalation of layered aluminosilicate containing 95wt% montmorillonite with mixed polymeric Fe,Cu,Al-polyoxocations (Al/(Fe+Cu)=10/1, OH/(Fe+Cu+Al)=2.0mol/mol). The materials were characterized by chemical analysis, low-temperature nitrogen adsorption and XRD. Fe/Cu/Al-pillared clays were active catalysts for sulfanilamide oxidation with hydrogen peroxide in aqueous solutions: in the presence of these materials oxidation rate increased significantly and conversion of sulfanilamide reached 99–100%. The effect of experimental factors such as H2O2/sulfanilamide molar ratio, the catalyst content, the reaction temperature and the pH on the conversion of sulfanilamide were studied. The optimal conditions for the catalytic oxidation of sulfanilamide in the presence of Fe/Cu/Al-pillared clay that permit achieving a high conversion of sulfanilamide and catalyst stability were determined. The Fe/Cu/Al-pillared clay could be used in four consecutive cycles without regeneration and loss of activity. The main intermediate products of sulfanilamide oxidative degradation were sulfanilic acid, benzenesulfonic acid, p-benzoquinone and aliphatic carboxylic acids. The results of the study proved that Fe/Cu/Al-pillared clays were effective catalysts for oxidative degradation of sulfanilamide in aqueous solutions.

Synthesis of highly dispersed iron species within mesoporous (Al-)SBA-15 silica as efficient heterogeneous Fenton-type catalysts

Iron and iron-aluminium containing ordered SBA-15 silica catalysts were synthesized for the first time at relatively high iron content (Si/Fe molar ratio down to ∼21) using an adapted two-step pH-adjustment approach needed for the incorporation of heteroatom species in the mesostructure. The pH applied for the second step of synthesis significantly affected (i) the content of inserted iron and (ii) the state of iron species. Thus, under acidic conditions, the iron heteroatoms were partly incorporated within the mesoporous SBA-15 structure. The solids displayed a moderate activity in the Fenton-type peroxidation of Reactive Red 120 azo dye owing to the low density of active sites for H2O2 activation. Nearly complete iron incorporation was achieved at slightly basic pH with iron mostly presented as isolated and/or highly dispersed species. Furthermore, it was observed that the co-addition of aluminium to iron significantly promoted stabilization of iron species in isolated and/or highly dispersed state, which exhibited improved catalytic properties for the dye degradation with fast cleavage of azo-chromophore into intermediates and high mineralization level.

Removal of diclofenac from water by zeolite-assisted advanced oxidation processes

Abstract The goal of the study was to evaluate the performance of zeolite-assisted advanced oxidation processes for the removal of diclofenac (DCF) in water matrix. Heterogeneous Fenton type catalyst (FeZSM5) was prepared by solid-state ion exchange and characterized by SEM/EDS and ICP/MS analyses. The uniform distribution of iron and atom economy was established. The influence of key operating parameters of applied UV-A/FeZSM5/H 2 O 2 process on the activity of zeolite catalyst was investigated using statistical modeling. The results obtained revealed the contribution of adsorption and oxidative degradation to the overall treatment effectiveness, whereas the oxidation became dominant at the end of the treatment. UV-A/FeZSM5/H 2 O 2 process applied at optimal conditions determined within the investigated range (pH 4, [H 2 O 2 ] = 50 mM and [Fe] FeZSM5 = 2.0 mM) resulted in significant improvement in biodegradability and lower toxicity after 2 h treatment of DCF aqueous solution. The used catalyst showed good stability and retained its catalytic activity in consecutive runs, which was documented by low iron leaching and similar consumption of oxidant in repetitive cycles.

Fe-silicalites as heterogeneous Fenton-type catalysts for radiocobalt removal from EDTA chelates

Fe-silicalite nano- and microcrystals as heterogeneous Fenton-type catalysts have been synthesized and characterized by dynamic light scattering, X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption measurements, inductively coupled plasma optical emission spectrometry, UV visible diffuse reflectance spectroscopy and temperature-programmed desorption of ammonia. Catalytic performance of Fe-silicalites was studied in mineralization of EDTA by H2O2 at 303–353K and 60Co removal from EDTA chelates. The effect of activation by the acid treatment on the state of active sites, catalytic activity and stability of Fe-silicalites was studied. Fe-silicalites nanocrystals are more efficient catalysts vs. microcrystals due to enhanced catalytic sites accessibility.

Fenton degradation of sulfanilamide in the presence of Al,Fe-pillared clay: Catalytic behavior and identification of the intermediates

Liquid phase catalytic degradation of sulfanilamide with H2O2 was carried out in the presence of Fe,Al/M-pillared clay (Fe,Al/M-MM, M=Na+, Ca2+ and Ba2+) as heterogeneous Fenton type catalyst. Fe,Al/M-MMs were prepared by swelling of layered aluminosilicate (90–95wt.% montmorillonite) from a bed located in Mukhortala (Buryatia, Russia) in Na+, Ca2+ and Ba2+ forms by means of the exchange of these cations with bulky Fe,Al-polyoxocations prepared at Al/Fe=10/1 and OH/(Al+Fe)=2.0, and then calcinated at 500°C. XRD method and chemical analysis demonstrated that the rate of crystalline swelling was dependent on the interlayer cations and decreased in the order: Fe,Al-/Na-MM>Fe,Al/Ca-MM>Fe,Al/Ba-MM. It was found that the catalytic properties of Fe,Al/M-MMs depended on the type of exchangeable cations. The effect of the H2O2/sulfanilamide molar ratio, the catalyst content, the reaction temperature and the reaction pH on the removal rate of sulfanilamide has been studied in the presence of Fe,Al/Na-MM. The catalyst can be applied for degradation of sulfanilamide with H2O2 for at least three successive cycles without loss of activity. HPLC analyses pointed out that the main degradation intermediate products were sulfanilic acid, benzenesulfonic acid, p-benzoquinone and aliphatic carboxylic acids.

Hierarchical zeolite FeZSM-5 as a heterogeneous Fenton-type catalyst

Series of hierarchical zeolites ZSM-5 and FeZSM-5 were prepared by hydrothermal treatment using polystyrene spheres template and characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, scanning and high-resolution transmission electron microscopies, and N2 sorption techniques. Walls of the macroporous structure consisted of ZSM-5 nanocrystals with a size of 20–300nm and amorphous globules of SiO2. Hierarchical FeZSM-5 contained iron in the form of iron oxide particles with a size of 2–3nm. Hierarchical zeolites had high values of surface area (437–613m2/g), external surface area (131–462m2/g), and pore volume (0.36–0.76cm3/g). Iron-containing zeolites were tested in the H2O2 decomposition reactions in the absence and presence of iron-complexing agent, as well as in oxidation of low and high molecular weight organic compounds by H2O2 at 25°C and compared with homogeneous Fe(NO3)3 solution. Hierarchy of the zeolite porosity resulted in a significant improvement of the catalyst properties.

Wastewater treatment with heterogeneous Fenton-type catalysts based on porous materials

The Fenton reagent which was discovered by H. J. H. Fenton over 100 years ago is still of special interest for wastewater treatment in the present time. The main objective of heterogeneous Fenton catalysts is the combination of high activity, low iron leaching and the possibility of employing the system at pH environments near neutrality. This review discusses the use of iron-containing pillared clays as well as micro- and mesoporous (alumino-) silicate catalysts prepared by ion-exchange, impregnation or direct synthesis for the degradation of organic compounds like phenol and organic dyes including Orange II. Moreover, the treatment of more complex waste streams is reviewed. After a general introduction into the chemistry of the Fenton and the photo-Fenton reaction as well as the catalysts employed, specific examples are discussed with respect to the active species present, the stability of the catalyst and the influence of reaction conditions such as pH, temperature and the presence of impurities.

The activation of heterogeneous Fenton-type catalyst Fe-MFI

Abstract The activation of iron-containing zeolite of MFI structure with mineral and carboxylic acids in heterogeneous Fenton reaction was experimentally studied. The catalytic activity of the zeolite was tested in the hydrogen peroxide decomposition reaction. The activation effect of acids was observed in the following decreasing order: oxalic > acetic > hydrochloric > formic. The catalyst pre-treatment with nitric acid was ineffective. Optimum conditions for the most effective pre-treatment of the zeolite with aqueous oxalic acid solutions were established.

Fe-exchanged zeolite as the effective heterogeneous Fenton-type catalyst for the organic pollutant minimization: UV irradiation assistance

The issue of investigations in this study was an application of heterogeneous Fenton-type catalyst, Fe-exchanged zeolite FeZSM5, for the minimization of phenol and overall organic content in the model wastewater. Applied treatment systems included variation of heterogeneous and homogeneous Fenton-type catalyst with and without the assistance of UV irradiation, FeZSM5/H 2O 2, Fe 2+/H 2O 2/NH 4ZSM5, Fe 3+/H 2O 2/NH 4ZSM5, UV/FeZSM5/H 2O 2, UV/Fe 2+/H 2O 2/NH 4ZSM5 and UV/Fe 3+/H 2O 2/NH 4ZSM5. Processes efficiency was evaluated on the basis of phenol removal, mineralization extent, H 2O 2 consumption and concentration of iron ions in the bulk after the treatment. By all applied systems, complete phenol removal was achieved in less than 30 min of treatment time. Systems including heterogeneous Fenton-type catalyst showed somewhat lower mineralization efficiency in comparison to the corresponding systems applying homogeneous Fenton-type catalysts and the addition of synthetic zeolite NH 4ZSM5. Significantly lower concentration of iron ions in the bulk after the treatment could give these systems, particularly UV/FeZSM5/H 2O 2, a great advantage over the homogeneous Fenton-type systems.

The catalytic and photocatalytic oxidation of organic substances using heterogeneous Fenton-type catalysts

This paper deals with catalytic and photocatalytic oxidation of organic substances using H202 over heterogeneous Fenton-type catalysts. In the study a series of Fe-containing catalysts was experienced. A zeolite named as FeZSM-5 was selected as the most active heterogeneous Fenton-type catalyst. The FeZSM-5 reported was prepared by hydrothermal crystallization in the presence of iron salt. In contrast to the homogeneous Fenton system the catalyst prepared had minimal, if any, leaching of iron ions, was stable during 30 catalytic runs and didn't lose its activity in the presence of complexing agents, e.g. P2O7(4-). The catalyst was active in oxidation of organic substances at pH from 1.5 to 8, maximum activity was observed at pH = 3. The FeZSM-5 effectively oxidized a simulant of the warfare agent, diethylnitrophenil phosphate, which is hardly detoxified by other methods. It appeared that the rate of oxidation of formic acid, ethanol and benzene over FeZSM-5 increased under the action of visible light (lambda > 436 nm), quantum efficiency being 0.06-0.14.

Catalytic wet oxidation with H 2O 2 of carboxylic acids on homogeneous and heterogeneous Fenton-type catalysts

The catalytic wet oxidation with hydrogen peroxide (WHPO) of diluted formic, acetic and propionic acid solutions (total organic carbon of 30 mg C/l) in the 25–70°C temperature range using a Fe 3+-containing zeolite (Fe/ZSM5) is compared with the behavior of homogeneous Fe 3+ catalysts at the same experimental conditions. Although the heterogeneous catalysts have a higher reactivity and a reduced dependence on the pH of the solution in comparison to the homogeneous Fe 3+ catalysts, they also have a higher rate of the side reaction of hydrogen peroxide decomposition to water and oxygen. Leaching tests indicate that the activity of the heterogeneous catalyst is not due to leached iron ions, although a small amount of iron was found in the aqueous solution. It was also observed that catalytic behavior could be reproduced in consecutive catalytic experiments, but an intermediate calcination step is necessary to oxidize the organic species which remain trapped inside the pore of the zeolite.