Catalysts For Wet Peroxide Oxidation Research Articles

Polyolefin-derived carbon nanotubes as magnetic catalysts for wet peroxide oxidation of paracetamol in aqueous solutions

This work deals with developing feasible valorization technologies to prepare carbon nanotubes (CNTs) from plastic solid waste and demonstrate their application in catalytic wet peroxide oxidation (CWPO). CNTs were synthesized by catalytic chemical vapor deposition (CCVD) at 850 ºC, considering low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) as carbon precursors representative of urban plastic solid waste. Iron oxide nanoparticles supported in alumina, previously synthesized by sol-gel, were used as catalysts in the CCVD process. TEM micrographs allow us to determine 41 nm as the average outer diameter of the CNTs and to visualize magnetic iron nanoparticles (ca. 10 nm) embedded inside the CNTs (ca. 6.4 % of content measured as ashes). These magnetic nanoparticles were kept in the CNT structure even after the purification of the CNTs with sulphuric acid, allowing to obtain magnetic CNTs. All purified and non-purified CNTs prepared from the polyolefins were assessed as catalysts in CWPO of paracetamol (PCM), used as a model pharmaceutical contaminant in water at CPCM,0 = 100 μg mL−1 (CH2O2,0 = 472 μg mL−1, CCNT = 2.5 g L−1, pH0 = 3.5 and T = 80 °C). The concentrations of PCM, H2O2, aromatic and total phenolic compounds were monitored for 24 h. All CNTs showed catalytic activity, allowing the complete degradation of PCM at 6 h of reaction time. The stability and reusability of materials are tested and proved in CWPO.

Cu- and Fe-substituted ZSM-5 zeolite as an effective catalyst for wet peroxide oxidation of Rhodamine 6 G dye

Several Cu-exchanged and Fe-exchanged ZSM-5 catalysts were prepared and studied for the decoloration, degradation and mineralization of Rhodamine 6 G in catalytic wet peroxide oxidation (CWPO). The Cu-ZSM-5 catalysts were shown to be more effective than the parent H-ZSM-5 zeolites (containing Fe-ions as impurity) and Fe-exchanged ZSM-5 to Rhodamine 6 G oxidation by hydrogen peroxide. Effects of copper loadings, Si/Al ratio, structure of copper species, and initial pH were ascertained on catalytic behavior of Cu-ZSM-5 and copper leaching under CWPO conditions. At acid pH, the highest decoloration of Rhodamine 6 G was typical of Cu-ZSM-5 with Si/Al equal to 30 and Cu content of ca. 0.5 – 0.65 wt% having isolated Cu2+ ions, whereas the maximal conversions of total organic carbon (TOC) were exhibited by catalysts with 1.5 – 2.8 wt% Cu and CuO-like clusters on the external zeolite surface. At alkali pH, the over-exchanged 2.8% Cu-ZSM-5 with CuO-like clusters was more active than under-exchanged 0.5% Cu-ZSM-5 to decoloration of Rhodimine 6 G, while both catalysts provided identical TOC conversions. Catalyst with 0.5 wt% copper loading showed reproducible activity up to 7th cycle. According to UV-Vis DR and EPR studies, the high efficiency of Cu-ZSM-5 to Rhodamine 6 G oxidation in acid solution is provided by the isolated Cu2+ ions, while the nanostructured square-planar CuO-like clusters (on the zeolite surface) ensure activity at alkali pH. Two mechanisms of organic substrate oxidation, i.e. radical (Fenton-like) mechanism activated by isolated Cu2+ ions and nucleophilic substitution via copper-hydroperoxide complex generation, were discussed.

Assisted hydrothermal carbonization of agroindustrial byproducts as effective step in the production of activated carbon catalysts for wet peroxide oxidation of micro-pollutants

This work deals with the valorisation of bagasse of sugarcane – BC, bagasse of malt – BM and seed of chia – SC, through its transformation into pyrochars, hydrochars and activated carbons (ACs) by pyrolysis, hydrothermal carbonization (HTC) and sequential HTC and pyrolysis, respectively. The HTC process was carried out in the presence of H2O, FeCl3 and H2SO4 solutions. The materials resulting by HTC in the presence of FeCl3 revealed the highest burn-off, but the contents of carbon released into the liquid phase, measured as total organic carbon, and to the gaseous phase, determined by carbon balance, depend strongly on the carbon precursor. In this sense, BC generates more volatile organic compounds (up to 34% of the initial carbon content), followed by BM (< 15%) and SC (< 5%) in their HTC and pyrolysis (70%). The pyrochars, hydrochars and ACs prepared from BC also show the highest specific surface areas (SBET < 447 m2·g−1) when compared to the specific surface areas of the materials prepared from BM and SC. The carbon-based materials prepared with FeCl3 show the highest catalytic activity, but iron leaching into solution is observed. On the other hand, the materials prepared with H2SO4 show high activity, enabling its application in successive cycles and the complete degradation of caffeine in concentrations ranging from 1 to 100 mg·L−1, after 5–60 min of reaction.

Catalysts Prepared with Matured Compost Derived from Mechanical-Biological Treatment Plants for the Wet Peroxide Oxidation of Pollutants with Different Lipophilicity

The current work proposes a strategy for the valorization of compost obtained from municipal solid waste, through its activation with H2SO4 and thermal treatment at 400–800 °C to produce low-cost catalysts for wet peroxide oxidation. All the developed materials were catalytically active for the aqueous solution oxidation of 2-nitrophenol (C2-NP,0 = 0.5 g L−1) and 4-nitrophenol (C4-NP,0 = 5.0 g L−1). In particular, using the catalysts prepared by thermal activation of the compost (with and without subsequent treatment with H2SO4), complete removal of both model pollutants was achieved after 24 h (at 50 °C, initial pH 3, Ccat = 2.5 g L−1, and employing a stoichiometric quantity of H2O2 needed for the total mineralization of the pollutants). In a cyclohexane–water mixture (simulating biphasic oily wastewater), 4-nitrophenol is also completely removed by the catalyst not treated with H2SO4. In contrast, the removal of 2-nitrophenol decreased to 93% due to its higher lipophilic character. Thus, this work demonstrates that active catalysts for wet peroxide oxidation can be obtained by using as a precursor a matured compost derived from municipal solid waste.

Carbon nanotubes as catalysts for wet peroxide oxidation: The effect of surface chemistry

Three magnetic carbon nanotube (CNT) samples, named A30 (N-doped), E30 (undoped) and E10A20 (selectively N-doped), synthesized by catalytic chemical vapor deposition, were modified by introducing oxygenated surface groups (oxidation with HNO3, samples CNT-N), and by heat treatment at 800 °C for the removal of surface functionalities (samples CNT-HT). Both treatments lead to higher specific surface areas. The acid treatment results in more acidic surfaces, with higher amounts of oxygenated species being introduced on N-doped surfaces. Heat-treated samples are less hydrophilic than those treated with nitric acid, heat treatment leading to neutral or basic surfaces, only N-quaternary and N-pyridinic species being found by XPS on N-doped surfaces. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L−1) at atmospheric pressure, T = 50 °C and pH = 3, using a catalyst load of 2.5 g L−1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. The high temperature treatment enhanced significantly the activity of the CNTs towards CWPO, evaluated in terms of 4-NP and total organic carbon conversion, due to the increased hydrophobicity of their surface. In particular, E30HT and E10A20HT were able to remove ca. 100% of 4-NP after 8 h of operation. On the other hand, by treating the CNTs with HNO3, the activity of the less hydrophilic samples decreased upon increasing the concentration of surface oxygen-containing functionalities, whilst the reactivity generated inside the opened nanotubes improved the activity of the highly hydrophilic A30 N.

Exploring the activity of chemical-activated carbons synthesized from peach stones as metal-free catalysts for wet peroxide oxidation

Peach stones were used as raw material for the synthesis of activated carbons with different properties. Firstly, peach stones were chemically activated using a 12 M H3PO4 solution and carbonized under flowing air (400 °C). The obtained activated carbon, named as PS, is characterized by a high surface development (SBET = 1262 m2 g−1) and acidic character (pHPZC = 4.2). A fraction of PS was further carbonized under N2 atmosphere at 800 °C to remove surface functionalities and to increase its basicity (PS-800). In addition, a Pt catalyst supported on PS (3% w/w Pt/PS) was synthesized by incipient wetness impregnation, resulting in a considerable hydrophilicity increasing. The synthesized materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated solutions of 4-nitrophenol (4-NP, 5 g L−1) during 24 h experiments, conducted at relatively mild operating conditions (T = 50–110 °C, pH = 3, catalyst load = 2.5 g L−1 and [H2O2]0 = 17.8 g L−1, corresponding to the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP). It was observed that the increase of electron-donating functionalities in PS-800 promotes the generation of reactive HO radicals, being the activity towards CWPO twice higher than that obtained with the pristine PS. Besides, increasing operating temperature substantially enhances CWPO, finding a 80% of 4-NP removal at 110 °C. On the other hand, despite the sharp increment in H2O2 decomposition due to the presence of Pt particles in Pt/PS catalyst, this decomposition is inefficient in all cases, with a consequent poor pollutant removal. This can be attributed to the recombination of HO radicals into non-reactive species −scavenging effects, promoted by the hydrophilicity of the catalyst.

Free- and Ni-doped carbon xerogels catalysts for wet peroxide oxidation of methyl orange

The present study investigates the synthesis and catalytic oxidation performance of catalysts consisting of free- and nickel-doped carbon xerogels (CXs) that derived from carbonization of tannic acid-resorcinol-formaldehyde xerogel at 700°C for 30min under N2 gas flowing. Nickel-doped carbon xerogels (CX-Ni-350 and CX-Ni-500) were prepared by wet impregnation-reduction method and then thermally treated at 350 and 500°C for 180min under its own atmosphere, respectively. The X-ray diffraction patterns (XRD) of the obtained CX-Ni-500 catalyst revealed that three nickel metallic phases were formed in carbon matrix indicating its profound affect to improve the catalytic activity of CX. Scanning electron microscope combined with energy-dispersive spectroscopy (SEM-EDS) also indicated that wide pores and nickel particles dispersed on the surface of produced CX-Ni-500 catalyst were found. To assess the catalytic efficiency of the prepared catalysts, catalytic wet peroxide oxidation of methyl orange dye was studied. It was found that decomposition rate of MO dye was strongly dependent on the hydrogen peroxide dose, temperature, catalyst dose and initial concentration of MO dye. The catalytic decomposition of MO dye was completely achieved in 30min by CX-Ni-500 at pH 3. The CWPO experimental results also showed that the incorporation of Ni metallic by impregnation-reduction method into CX surface dominated the decomposition efficiency of MO dye. To estimate the reusability efficiency of the prepared CX-Ni-500 catalyst, the results showed excellent catalytic activity during four CWPO cycles, affording highly decomposition of MO dye over 90% within the fourth CWPO run.

Catalytic degradation of chlorinated organic pollutants over CexFe1−xO2 (x: 0, 0.25, 0.5, 0.75, 1) nanocomposites at mild conditions

Oxidation of chlorinated organic pollutants (COPs) like 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4-dichlorophenoxy acetic acid (2,4-D) using aqueous hydrogen peroxide (30% v/v) over CexFe1−xO2 (x: 0, 0.25, 0.5, 0.75, 1) nanocatalysts was studied. The catalysts were characterised by temperature programmed reduction (H2-TPR) and desorption (NH3-TPD and CO2-TPD) techniques. The reducing power of ceria increased on iron doping as revealed by TPR analysis. CexFe1−xO2 were effective catalysts for Wet Peroxide Oxidation of 4-CP, 2,4-DCP and 2,4-D pollutants. 4-CP (500mg/L) was completely degraded with 37.38% TOC and 58.75% COD removal after 90min at 70°C using Ce0.25Fe0.75O2 catalyst. Complete 2,4-DCP (250mg/L) conversion with 21.60% TOC and 42.44% COD removal was observed at 45min over Ce0.5Fe0.5O2 catalyst at 50°C. 100% catalytic oxidative conversion of 2,4-D (250mg/L) with 23.64% TOC and 45.78% COD removal was achieved at 70°C at 60min. Atomic Absorption Spectrometry (AAS) indicated the extent of leaching of iron from the catalytic structure to be negligible. The mixed oxides were reusable and stable on consecutive uses as indicated by X-ray diffraction (XRD) and surface area measurements. The catalytic efficiency was retained after five successive runs.

CexV1−xO2 (x: 0, 0.25–1) nanocomposites as efficient catalysts for degradation of 2,4 dichlorophenol

Composite oxides of CexV1−xO2 (x: 0, 0.25–1) were synthesized, characterized and applied for removal of 2,4-dichlorophenol. The catalysts were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), N2 adsorption at −196°C, Fourier transform Infra Red (FT-IR) and Fourier Transform Raman (FT-Raman) techniques. The X-ray diffractograms of Ce –V oxide powders with different Ce/V molar ratios revealed the coexistence of CeO2 with a tetragonal CeVO4 and orthorhombic V2O5 phase. The Brunauer–Emmet–Teller (BET) surface areas and pore volumes of synthesised composites were in the range of 26.21–1.26m2/g and 0.01–0.0007cm3/g respectively. FT-Infra Red and FT-Raman measurements confirmed the formation of different mixed oxides. Effects of Ce-V ratio, H2O2 dose, reaction temperature, and 2,4-dichlorophenol (2,4-DCP) concentration on CWPO of 2,4-DCP were investigated in detail. CexV1−xO2 were effective catalysts for wet peroxide oxidation of 2,4-DCP and the highest catalytic activity was obtained using the Ce0.5V0.5O2 catalyst with complete 2,4-DCP degradation at 60min, and at 180min COD and TOC removal percentage was 84% and 41.03% respectively. Atomic Absorption Spectrometry (AAS) indicated the extent of leaching of vanadium to be negligible. The mixed oxides were reusable and stable on consecutive use as indicated by XRD and surface area measurements.

Cu and Fe-containing ZSM-5 zeolites as catalysts for wet peroxide oxidation of organic contaminants: reaction kinetics

The peroxide oxidation of model substrates (formic acid and phenol) was studied in the presence of copper- and iron-containing catalysts (0.5 % Cu–ZSM-5-30 and 0.65 % Fe–ZSM-5-30). The aim was to develop optimal kinetic models for describing the kinetics of peroxide oxidation. The real kinetics of phenol and formic acid oxidation in the presence of these catalysts at varied reaction parameters (concentrations and temperature) was studied. The copper-containing catalysts were more active to formic acid oxidation than the iron-containing catalyst over all the temperature range studied. The rate of destruction of pollutants decreases with a decrease in the H2O2 concentration and the catalyst weight. The observed rate dependences on the initial substrate concentration appeared to be different for the substrate used. With formic acid, an increase of initial concentration leads to a slight increase in the reaction rate. In the case of phenol peroxide oxidation, the negative order with respect to the substrate concentration was observed. This may be explained by strong inhibition of the reaction rates by phenol and intermediates (hydroquinone, catechol, etc.) of its oxidation. The mathematical modeling of the kinetics was performed for various types of kinetic equations that correspond to different hypotheses on the kinetic reaction scheme. The selected kinetic models based on logical kinetic schemes allowed describing the peroxide oxidation of model substrates at an appropriate accuracy.

Manganese zinc ferrite nanoparticles as efficient catalysts for wet peroxide oxidation of organic aqueous wastes

Manganese substituted zinc nanoparticles, MnxZn1−xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0) prepared by sol gel method were found to be efficient catalysts for wet peroxide oxidation of 4-chlorophenol. Complete degradation of the target pollutant occurred within 90 min at 70∘C. Zinc substitution enhanced the catalytic efficiency and the unsubstituted ZnFe2O4 oxidized the target compound completely within 45 min. Studies on the effect of reaction variables revealed that only a small amount of the oxidant, H2O2 (3–4 mL) is required for complete degradation of 4-chlorophenol. More than 80% of 4-chlorophenol was removed at catalyst concentrations of 100 mg/L. Direct correlation between the amount of catalyst present and the extent of degradation of 4-chlorophenol was observed, ruling out hesterogeneous-homogeneous mechanism. The catalysts are reusable and complete degradation of target pollutant occurred after five successive runs. The extent of iron leaching was fairly low after five consecutive cycles indicating the mechanism to be heterogeneous.

Carbon nanotubes as catalysts for catalytic wet peroxide oxidation of highly concentrated phenol solutions: towards process intensification

Commercial multi-walled carbon nanotubes with different properties (two samples from Sigma-Aldrich, SA1 and SA2; one sample from Nanocyl, NC; and two samples from Shenzhen Nanotech, SZ and LSZ), and SA2 modified by hydrothermal treatment with concentrated sulfuric acid (SA2-H), were tested as catalysts in wet peroxide oxidation. Phenol was selected as model compound since it represents a class of noxious compounds for human health and for the environment and, due to this, phenol is typically considered in wastewater treatment studies. The experiments were carried out under the following intensified conditions: phenol concentration=4.5gL−1, hydrogen peroxide concentration=25gL−1, catalyst load=2.5gL−1, pH 3.5, T=353K and 24h.The results demonstrated that phenol is poorly adsorbed in this type of carbon materials (11% as maximum when using the NC sample). However, in the catalytic experiments, complete removal of phenol is achieved when using some of the carbon nanotubes (SA1, NC and SA2), together with a remarkable total organic carbon removal (77, 69 and 67%, respectively). These materials have the less pronounced acidic character, which is often considered favorable for oxidation reactions in advanced oxidation processes and may explain the higher performance of SA1, NC and SA2 regarding the other materials. Leaching of Fe species into the solution was also observed in all cases (that can also have some influence on the degradation of phenol), SA1 leading to the highest concentration of Fe species leached (26mgL−1), followed by SA2 (2mgL−1) and NC (1mgL−1).Considering the lower Fe leaching levels observed for SA2 and NC, these catalysts were then tested in consecutive reusability cycles. SA2 showed a superior performance than NC, but temperature-programmed desorption as well as thermogravimetric analysis suggested that the carbon material is oxidized by hydrogen peroxide at the employed conditions and/or that carboxylic acids are adsorbed on the catalyst surface after consecutive runs (mainly after the first use). However, only a slight decrease in the catalyst activity was observed.

Graphite and carbon black materials as catalysts for wet peroxide oxidation

This study explores the application of non-porous carbon materials, two graphites (G-F, G-S) and two carbon blacks (CB-V and CB-C) as catalysts for wet peroxide oxidation (CWPO). The activity, efficiency and stability of these carbon materials have been evaluated using phenol as target compound. The catalyst screening experiments were carried out batch-wise at CPhenol,0=1g/L, CH2O2,0=5 g/L, Ccat=2.5g/L, T=80°C and pH0=3.5. The results allow concluding that CB-C was the most stable catalyst, although it showed a lower oxidation and mineralization activity than G-S and CB-V. Increasing the temperature up to 90°C allowed complete phenol conversion and around 70% TOC reduction with 100% efficiency of hydrogen peroxide consumption upon 20h reaction time at 5g/L CB-C load. As a consequence of the initial oxidation of the carbon surface, the electrochemical properties of CB-C were favorably changed upon CWPO and its catalytic performance was improved from the first to the second use and then maintained upon successive applications in a five-cycle test.

Highly efficient application of activated carbon as catalyst for wet peroxide oxidation

This paper addresses the improved performance of activated carbons in catalytic wet peroxide oxidation (CWPO) of phenol as target compound. Initial cyclic voltammetry experiments show that hydrogen peroxide and phenol compete for the same active sites on the carbon surface. Then, a significant coverage of the carbon surface by phenol molecules is the approach attempted to increase the efficiency of hydrogen peroxide and the performance of the oxidation process.In this work, two commercial activated carbons, with different physical and electrochemical properties have been tested. The results demonstrate that working at high phenol concentration (5g/L) and phenol/carbon mass ratio (2), unprecedented hydrogen peroxide efficiencies of around 100% are achieved, allowing high oxidation and mineralization degrees, i.e. 97% phenol and 70% TOC conversions at 80°C with the stoichiometric dose of hydrogen peroxide required for complete mineralization of phenol. The oxidation route of phenol in the presence of activated carbon is also studied and a reaction pathway proposed. Resorcinol was a new by-product detected whose formation occurs upon reaction on the carbon surface. Condensation by-products, typically formed in Fenton oxidation of phenol, were not found in the effluents but adsorbed on the carbon surface causing a progressive deactivation upon use. The activity can be easily recovered by oxidative thermal regeneration (350°C, 24h).

Cu-containing MFI zeolites as catalysts for wet peroxide oxidation of formic acid as model organic contaminant

The catalytic behavior of different Cu(Fe)/zeolite catalysts with the MFI morphology in wet peroxide oxidation of formic acid as a model organic substrate was thoroughly examined. The influence of the method for Cu2+ ions introduction into the zeolite matrix, Cu loading and the electron state of Cu on catalytic properties of zeolites, including their stability to leaching of Cu was studied. Cu-substituted ZSM-5 zeolites with the atomic ratio Si/Al=30 and Cu content of 0.5–1.5, which were prepared by ion exchange, were shown most promising for wet peroxide oxidation. The impact of temperature, initial pH and concentrations of reagents on the catalytic performance of the catalyst with the optimal composition also was studied. The characterization of fresh and spent catalysts using UV–vis DR and ESR spectroscopic techniques led to suppose that the high efficiency of Cu-ZSM-5 to redox reactions in aqueous media is provided by nanostructured square-planar copper oxide clusters localized in the zeolite channels.

Supported gold nanoparticle catalysts for wet peroxide oxidation

Supported gold nanoparticles are of promising interest in wet hydrogen peroxide oxidation processes due to their efficient hydrogen peroxide consumption and adequate stability. Here, the origin of the catalytic properties of gold in this environmental process is explored by analyzing the influence of the support and the particle size on the activity of supported gold nanoparticles along with the influence of the nature of the target pollutant on the gold reactivity. The reaction mechanism for the oxidation of phenol with activated carbon-supported gold nanoparticles is proposed and the selectivity evaluated. A reaction pathway has been also proposed.The results demonstrate that wet peroxide oxidation is a support and gold size dependent reaction. Activated carbon is the preferable candidate versus TiO2 and Fe2O3 supports and small gold nanoparticles, desirably lower than 3nm, show the highest TOF values. Supports showing adsorption capacity towards the target pollutant contribute to a more efficient use of hydrogen peroxide and, improve the TOF values for the oxidation and mineralization. Organic pollutants forming intermediate complexes with gold, viz. alcohols, are more efficiently oxidized. The inclusion of gold improves substantially the selectivity towards mineralization with respect to the bare activated carbon.

Fe Containing ZSM-5 Zeolite as Catalyst for Wet Peroxide Oxidation of Orange II

Fe Containing ZSM-5 Zeolite as Catalyst for Wet Peroxide Oxidation of Orange II

Fe Containing ZSM-5 Zeolite as Catalyst for Wet Peroxide Oxidation of Orange II

This study presents the catalytic performances of iron containing ZSM-5 zeolites, prepared by ion exchange or hydrothermal synthesis, in catalytic Fenton-like oxidation of Orange II in aqueous solution. The catalyst, ZSM-5 zeolite with Si/Al ratio of 42 loaded with iron by ion exchange, showed the highest activity. The decolorization of 99.7 percent, degradation of 87.0 percent and COD removal of 81.2 percent were achieved over this catalyst at an initial pH of 3.5. Incorporation of iron into ZSM-5 structure increased its catalytic activity. The hydrothermally prepared FeZSM-5 catalyst was more stable against leaching at low pH value due to the iron being in the framework.

Fe-Zeolites as Catalysts for Wet Peroxide Oxidation of Organic Groundwater Contaminants: Mechanistic Studies and Applicability Tests

Two types of iron-containing zeolites, Fe-ZSM5 and Fe-Beta, were tested as catalysts for wet peroxide oxidation of organic groundwater contaminants such as trichloroethene (TCE) and methyl tert-butyl ether (MTBE) at nearly neutral pH. Adsorption of TCE is more favorable on the ZSM5 zeolite whereas MTBE is effectively adsorbed on Beta zeolite. Batch experiments showed that the efficiency of utilization of H2O2 for contaminant degradation is more favorable for the catalyst with the higher adsorptive enrichment of the respective contaminant. Laboratory-scale column experiments, including the use of contaminated groundwater, were conducted in order to test the stability of the Fe-zeolites under flow-through conditions.

Influence of OH/metal ratio on the stability of alfe-pilc catalyst for wet peroxide oxidation of phenol

AlFe-pillared clay catalyst with OH/metal = 4; 5 mmol metal/g clay and Al : Fe = 5:5 swells intensively in phenol-water solution and has no measurable catalytic activity in phenol removal from water solutions, on contrast to the similar catalyst with OH/metal = 2. The different behavior of two samples can be explained first of all by differences in iron ion distribution in catalysts as a consequence of applied pillaring solutions prepared at different OH/metal ratios. In the sample with OH/metal = 2 iron ions are uniformly distributed on the AlFe-pillars, while in the sample with OH/metal = 4 iron ions appear not only on the pillars but also as a bulk FeO.Fe2O3-form. The results obtained by FTIR, SEM, TPR and Mossbauer spectroscopy reveal the differences in acid-base properties, morphology and iron ion distribution in the samples.