Search Results (41)

Copper-based catalysts supported on γ-Al₂O₃ were prepared by wet impregnation and evaluated for the catalytic wet peroxide oxidation (CWPO) of phenol. Citric acid was used as a complexing agent to enhance copper stabilization, and lanthanum was incorporated as a structural promoter. The effects of calcination temperature, heating rate, Cu loading, and La incorporation route on catalyst structure and performance were systematically investigated. Thermal treatment and La incorporation-controlled phase evolution and copper oxidation state. Calcination at 900 °C promoted the development of CuAl₂O₄- and CuAlO₂-type phases, as suggested by XRD, while XPS showed that the Cu²⁺/Cu⁺ ratio increased progressively with temperature, consistent with stronger metal–support interactions. Citric acid, incorporated at a CA:Cu molar ratio of 1:1, reduced copper leaching by up to 50% compared to catalysts prepared without the complexing agent, regardless of calcination temperature. Co-impregnated Cu–La catalysts achieved complete phenol conversion within 20–30 min and TOC removals of 84–95%, depending on synthesis conditions. The combination of La incorporation, calcination at 900 °C, and citric acid-assisted impregnation yielded the best stability–activity balance, with Cu5.0/La-A-900-1 showing 91% TOC removal and only 18% Cu leaching after 2 h of reaction. XPS, catalytic performance, and leaching results indicate that CWPO activity is governed by the balance between redox accessibility (Cu²⁺/Cu⁺) and structural stabilization of copper species. The results indicate that CWPO proceeds through a combined surface-mediated and homogeneous Fenton-like pathway, where the relative contribution of each depends on copper stabilization and leaching. Full article

The purpose of this work was to develop and study catalytically active magnetic composites based on natural clays of Kazakhstan for their use in the process of catalytic wet peroxide oxidation (CWPO) of organic dyes. The synthesized materials, MnFe₂O₄/Shymkent and MnFe₂O₄/Ural, were obtained by intercalation of Fe²⁺, Fe³⁺, and Mn²⁺ ions into the interlayer spaces of natural aluminosilicates followed by heat treatment at 500 °C. The phase composition, morphology, and functional groups of the studied samples were characterized by the methods of elemental composition, X-Ray phase analysis, scanning electron microscopy, IR Fourier spectroscopy, and thermogravimetric analysis. The catalytic activity of the modified clays was evaluated in the decomposition reaction of methylene blue (MB) using hydrogen peroxide. To identify the influencing factors, adsorption experiments were conducted, including studying the effect of the adsorbent dose, the effect of pH on the degree of MB removal, and evaluating the activity of modified clays during the CWPO process under mild reaction conditions. The experiments were carried out at an initial dye concentration of C₀ = 50 mg/L, a catalyst dose of 0.25, 0.5, and 2.5 g/L, pH = 3 and 6, and a temperature of 50 °C. It was found that the degree of MB removal in adsorption experiments reaches 70% at a dose of 0.25 g/L and increases to 97.8–99% at 2.5 g/L. In terms of CWPO, with the addition of H₂O₂ complete degradation of MB was achieved within 120 min for MnFe₂O₄/Shymkent and 150 min for MnFe₂O₄/Ural. The high efficiency of the modified clays is explained by the formation of the MnFe₂O₄ ferritic spinel structure, an increase in porosity, specific surface area and hydrophilicity, as well as an improvement in the acid-base properties of the surface. The TGA results showed an increase in the thermal stability and uniformity of the composites. Thus, the developed magnetic composites can be considered as promising materials for the effective removal of organic pollutants from wastewater under mild CWPO conditions. Full article

Rouaite (Cu₂(OH)₃NO₃) long hexagonal multilayered nanoplates with high purity and high crystallinity were prepared from acidic reaction solution (pH = 4.4–4.8) with the assistance of ZnO. The ZnO-assisted strategy is remarkably different from the conventional synthetic protocol that was regularly carried out in alkaline solution (pH > 11). The rouaite multilayer nanoplates displayed exceptionally high catalytic activity in the catalytic wet peroxide oxidation (CWPO) of Congo red (CR). The catalytic efficiency for CR decolorization achieved an impressive 96.3% in 50 min under near-neutral (pH = 6.76) and ambient conditions (T = 20 °C, p = 1 atm), without increasing the temperature and/or decreasing the pH value to acidic region (pH = 2–3) as is commonly employed in CWPO process for improved degradation efficiency. Full article

Nanopowders of hydroxyapatite (HA) and Fe-substituted hydroxyapatite (HAFe) were synthesized by wet precipitation on either MCM-41 (a synthetic, mesoporous aluminosilicate material) or an aluminum-containing MCM-41 (AlMCM) support. According to X-ray diffraction data, all of the synthesized materials are composite powders consisting of amorphous silicate and an HA phase with low crystallinity. The presence of aluminum and iron in the structure of the powders resulted in further amorphization. The obtained samples showed high specific surface areas (SSAs), ranging from 162.3 to 186.6 m²/g for MCM-41-HA and from 112.6 to 127.2 m²/g for AlMCM-HA. The hysteresis loops were found to be of type H3, indicating the formation of slit-like pores in the intercrystalline space, as confirmed by transmission electron microscopy, which revealed the presence of lamellar and flake-like particles. Catalytic activity tests showed that the conversion of dibenzothiophene depended on the iron concentration in the material and the acidity of the support. To further improve the catalytic activity of the materials, they were impregnated with molybdenum compounds. Active molybdenum peroxo complexes formed under these conditions enabled 100% conversion of dibenzothiophene. To our knowledge, this is the first study on the influence of MCM-41-HA- or AlMCM-HA-based materials on dibenzothiophene conversion via oxidative desulfurization using hydrogen peroxide as an oxidant. Full article

Nitrophenols are persistent organic pollutants that pose serious environmental and health risks due to their toxic and lipophilic nature. Their persistence arises from strong aromatic stability and resistance to biodegradation, while their lipophilicity facilitates bioaccumulation, exacerbating ecological and human health concerns. To address this challenge, this study focuses on the synthesis and characterization of two different types of hybrid multi-core magnetic catalysts: (i) cobalt ferrite (Co-Fe₂O₄), which exhibits ferrimagnetic properties, and (ii) magnetite (Fe₃O₄), which demonstrates close superparamagnetic behavior and is coated with a novel and less hazardous phloroglucinol–glyoxal-derived resin. This approach aims to enhance catalytic efficiency while reducing the environmental impact, offering a sustainable solution for the degradation of nitrophenols in aqueous matrices. Transmission electron microscopy (TEM) images revealed the formation of a multi-core shell structure, with carbon layer sizes of 6.6 ± 0.7 nm for cobalt ferrite and 4.2 ± 0.2 nm for magnetite. The catalysts were designed to enhance the stability and performance in catalytic wet peroxide oxidation (CWPO) processes using sol–gel and solution combustion synthesis methods, respectively. In experiments of single-component degradation, the carbon-coated cobalt ferrite (CoFe@C) catalyst achieved 90% removal of 2-nitrophenol (2-NP) and 96% of 4-nitrophenol (4-NP), while carbon-coated magnetite (Fe₃O₄@C) demonstrated similar efficiency, with 86% removal of 2-NP and 94% of 4-NP. In the multi-component system, CoFe@C exhibited the highest catalytic activity, reaching 96% removal of 2-NP, 99% of 4-NP, and 91% decomposition of H₂O₂. No leaching of iron was detected in the coated catalysts, whereas the uncoated materials exhibited similar and significant leaching (CoFe: 5.66 mg/L, Fe₃O₄: 12 mg/L) in the single- and multi-component system. This study underscores the potential of hybrid magnetic catalysts for sustainable environmental remediation, demonstrating a dual-function mechanism that enhances catalytic activity and structural stability. Full article

In recent years, efforts have been made in developing new and more efficient water purification methods and the synthesis of catalysts with greater catalytic activity that are more stable and can be used in wide pH ranges. Pillared clays represent a viable alternative for removing organic contaminants. The clays, usually smectites, are modified by inserting inorganic pillars (Al, Zr, Cr, Fe, Ti, Ga, and Mn) between the layers of the clay, increasing its surface area, porosity, catalytic activity, and thermal stability. This review describes the importance of using pillared clays with different polyoxycations in Fenton, photo-Fenton, ozonation, wet catalytic oxidation of hydrogen peroxide, and photocatalysis processes. Pillared iron clays (Fe-PILCs) are promising catalysts capable of generating hydroxyl radicals that can oxidize organic contaminants, thus facilitating their removal. The current challenges of the PILC application at industrial scale are also discussed. Full article

Zinc-substituted cobalt ferrites were obtained by a green method using a black grape extract as a reductant and fuel. XRD analysis confirmed the spinel structure of the synthesized ferrites. An increase in the lattice constant is explained by increased Zn content. SEM analysis confirmed changes in surface morphology, whereas FTIR spectra demonstrated the presence of organic species in the samples, which originated from grape extract. The content of Co(II) ions in octahedral sites as a function of the ratio between Fe(III) ions in A- and B-sites was calculated from Mössbauer data. pH_PZC rose from 7.85 to 8.13 with an increase in zinc content, indicating a positive charge of the adsorbent surface at natural pH. The adsorption–catalytic properties of the spinel samples were investigated in terms of Congo Red (CR) dye removal. The mechanism of CR adsorption on the ferrite surface includes electrostatic and donor–acceptor interactions with the adsorbent surface. Furthermore, the sample with x(Zn) = 0.4 exhibited the highest degradation rate constant k = 0.102 min⁻¹ in the peroxide oxidation of CR, whereas the sample with x(Zn) = 1.0 exhibited the highest adsorption capacity. The electron transfer between ferrite samples and hydrogen peroxide was evidenced using electrochemical tests. The green-synthesized Co-Zn ferrites demonstrate a big potential as adsorbents/catalysts for water treatment. Full article

In this study, we investigated the catalytic properties of mono- and bimetallic palladium (Pd) and platinum (Pt) nanoparticles deposited via supercritical fluid reactive deposition (SFRD) on titanium dioxide (TiO₂) powder. Transmission electron microscopy analyses verified that SFRD experiments performed at 353 K and 15.6 MPa enabled the deposition of uniform mono- and bimetallic nanoparticles smaller than 3 nm on TiO₂. Electron-dispersive X-ray spectroscopy demonstrated the formation of alloy-type structures for the bimetallic PdPt nanoparticles. H₂O₂ is an excellent oxidizing reagent for the production of fine and bulk chemicals. However, until today, the design and preparation of catalysts with high H₂O₂ selectivity and productivity remain a great challenge. The focus of this study was on answering the questions of (a) whether the catalysts produced are suitable for the direct synthesis of hydrogen peroxide (H₂O₂) in the liquid phase and (b) how the metal type affects the catalytic properties. It was found that the metal type (Pd or Pt) influenced the catalytic performance strongly; the mean productivity of the mono- and bimetallic catalysts decreased in the following order: Pd > PdPt > Pt. Furthermore, all catalysts prepared by SFRD showed a significantly higher mean productivity compared to the catalyst prepared by incipient wetness impregnation. Full article

It is very important to choose a suitable method and catalyst to treat coking wastewater. In this study, Fe–Ce–Al/MMT catalysts with different Fe/Ce molar ratios were prepared, characterized by XRD, SEM, and N₂ adsorption/desorption, and treated with coking wastewater. The results showed that the optimal Fe–Ce–Al/MMT catalyst with a molar ratio of Fe/Ce of 7/3 has larger interlayer spacing, specific surface area, and pore volume. Based on the composition analysis of real coking wastewater and the study of phenol simulated wastewater, the response surface test of the best catalyst for real coking wastewater was carried out, and the results are as follows: initial pH 3.46, H₂O₂ dosage 19.02 mL/L, Fe²⁺ dosage 5475.39 mL/L, reaction temperature 60 °C, and reaction time 248.14 min. Under these conditions, the COD removal rate was 86.23%. Full article

Quinoline (QN) is highly toxic and carcinogenic and has been detected in soil, groundwater, and biological tissues. Advanced oxidation processes (AOPs) have shown promise to address its degradation in wastewater treatment, with catalytic wet peroxide oxidation (CWPO) being highlighted due to its cost-effectiveness and mild operation. However, developing active and inexpensive catalysts is crucial for CWPO’s effectiveness. Another pressing issue is the accumulation of mixed, dirty plastic solid waste (PSW), particularly polyolefins used in packaging. Although recycling rates have increased, much plastic packaging remains in landfills. However, polyolefins can be converted into carbon-based nanostructured materials (CNMs), such as carbon nanotubes (CNTs), through chemical vapor deposition (CVD) using PSW as a carbon precursor. While many studies focus on CNT preparation, their application is often overlooked. In this context, this work proposes the preparation of CNMs, particularly CNTs, through CVD using a single-stage pyrolysis reactor. Polyolefins (LDPE, HDPE, and PP), both individually and in a mixture simulating PSW, were used as carbon sources. Given a sufficiently high temperature, the desired CNT architecture was successfully synthesized regardless of the starting polymer. These CNMs were then tested as catalysts for CWPO in simulated wastewater containing QN. The results showed a rapid degradation of QN (30–120 min) and high removals of total organic carbon (TOC) and aromatic compounds (75% and >90%, respectively), demonstrating the applicability of PSW-derived CNTs in the CWPO process for QN abatement. Full article

Supported Pd/CeO₂ catalytic systems have been widely investigated in the low-temperature oxidation of CO (LTO CO) due to the unique oxygen storage capacity and redox properties of the ceria support, which highly influence the structural, chemical and electronic state of Pd species. Herein, operando near-ambient pressure XPS (NAP-XPS) technique has allowed the study of a conventional Pd/CeO₂ catalyst surface during the CO oxidation reaction under experimental conditions closer to the actual catalytic reaction, unfeasible with other surface science techniques that demand UHV conditions. SEM, HRTEM and XRD analyses of the powder catalyst, prepared by conventional incipient wetness impregnation, reveal uniformly CeO₂-loaded Pd NPs of less than 2 nm size, which generated an increase in oxygen vacancies with concomitant ceria reduction, as indicated by H₂-TPR and Raman measurements. Adsorbed peroxide (O₂²⁻) species on the catalyst surface could also be detected by Raman spectra. Operando NAP-XPS results obtained at the ALBA Synchrotron Light Source revealed two kinds of Pd species under reaction conditions, namely PdO_x and Pd^II ions in a Pd_xCe_1−xO_2−δ solution, the latter one appearing to be crucial for the CO oxidation. By means of a non-destructive depth profile analysis using variable synchrotron excitation energies, the location and the role of these palladium species in the CO oxidation reaction could be clarified: PdO_x was found to prevail on the upper surface layers of the metallic Pd supported NPs under CO, while under reaction mixture it was rapidly depleted from the surface, leaving a greater amount in the subsurface layers (7% vs. 12%, respectively). On the contrary, the Pd_xCe_1−xO_2−δ phase, which was created at the Pd–CeO₂ interface in contact with the gas environment, appeared to be predominant on the surface of the catalyst. Its presence was crucial for CO oxidation evolution, acting as a route through which active oxygen species could be transferred from ceria to Pd species for CO oxidation. Full article

Fluorinated Fe₃O₄ microspheres with 7.1 ± 1.4 wt% of fluoride (F-Fe₃O₄-1) were prepared via glycothermal synthesis. Fluorination significantly enhanced the activity of F-Fe₃O₄-1 in catalytic wet peroxide oxidation of anionic dyes (including orange G (OG) and congo red) at pH ~7. However, the promotional effect of fluorination became less obvious for amphoteric rhodamine B and was not observed for cationic methylene blue. After reacting with H₂O₂ (40 mM) for 2 h at pH 6.5 and 40 °C, the decolorization rates of OG (0.1 mM) and the pseudo-first-order rate constant were 96.8% and 0.0284 min⁻¹ over F-Fe₃O₄-1 versus 17.6% and 0.0011 min⁻¹ over unmodified Fe₃O₄. The effects of reaction parameters (initial H₂O₂ concentration and pH value and reaction temperature) on OG decolorization with H₂O₂ over F-Fe₃O₄-1 were investigated. The reusability of F-Fe₃O₄-1 was demonstrated by OG decolorization in eight consecutive runs. Fluorination increased the isoelectric point of F-Fe₃O₄-1 to 8.7 and facilitated the adsorption and degradation of anionic dyes on the surface of F-Fe₃O₄-1 at pH ~7. Scavenging tests and EPR spectra supported that hydroxyl radicals were the main reactive species for the OG decolorization over F-Fe₃O₄-1. Full article

In this study, natural Algerian kaolin was used as a support and impregnated with nickel at different loading amounts (2 wt.%, 5 wt.%, and 7 wt.%) in order to prepare a supported catalyst. The wet impregnation technique was used in this preparation; nickel oxide (NiO) was the active phase precursor of the catalyst, and the catalysts were designated as follows: 2%, 5%, and 7% Ni/kaolin. These catalysts were put to the test in catalytic wet peroxide oxidation (CWPO) for degrading the organic contaminant malachite green dye (MG). Analytical techniques such as FTIR spectroscopy, X-ray diffraction, BET, and X-fluorescence were used to examine the structure, morphology, and chemical composition of the support and the produced catalysts. Several parameters, including temperature, catalytic dose, metal loading, hydrogen peroxide volume, and kinetic model were systematically investigated. The combination of improved parameters resulted in a significant increase in the catalytic activity, achieving a high removal rate of MG dye of 98.87%. Full article

To improve the catalytic efficiency and decrease the reaction temperature of wet air oxidation technology, a Cu₂O/Al₂O₃ coating was prepared on the surface of aluminium alloys by anodizing technology, and subsequent heating treatment. Then, the Cu₂O/Al₂O₃ coating and 3 wt.% H₂O₂ was used to degrade methyl orange. The influence of the coating’s microstructure, crystalline component on the degradation rate of the methyl orange was studied. The microstructure of the coating was observed by scanning electron microscope. Results proved that the coating was composed of micropores, and Cu₂O was evenly dispersed on the surface and pores in the Al₂O₃ coating. X-ray diffraction pattern analysis demonstrated Cu₂O and Al₂O₃ characteristic peaks were found after the coating was treated at 300 °C, showing that amorphous Cu₂O and Al₂O₃ were transformed into crystalline oxide. A UV-vis spectrophotometer was used to measure the absorbance of methyl orange, and it was found that the maximum absorption wavelength of methyl orange is 460 nm. At that wavelength, the suitable degradation condition of methyl orange was studied, and results showed that when electrochemical deposition time was 30 min and catalyst dosage was 8 g, the degradation rate of methyl orange could reach 92% at 25 °C for 120 min. Furthermore, when the catalyst was reused 9 times, the degradation rate still reached 75%. Based on the above results, a kinetic equation between the degradation rate of methyl orange and catalyst dosage was derived. The microstructure and crystalline component of the catalyst after different reuse times were characterized, and results showed that the catalytic efficiency of the Cu₂O/Al₂O₃ coating decreased with a decrease in the coating’s specific surface area and the ratio of Cu₂O in the coating. Full article

Natural bearing (raw and calcined at 500 °C) and iron-enriched (impregnation and pillaring) montmorillonitic clay samples were prepared. The obtained samples were characterized (X-ray diffraction, Fourier Transformed Infrared Spectroscopy, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy) and evaluated as catalysts in catalytic wet oxidation of Brilliant Green and Crystal Violet. Experiments were conducted in the same conditions (0.5 g catalysts, 300 mL air/min or 0.5 mL H₂O₂, 25 mL of dye solution, 25 °C, initial solution pH = 6.0, for 3 h) in thermostated batch reaction tubes. Process evolution was followed using UV-Vis spectrometry (200–1100 cm⁻¹) and total organic carbon. Dye removal efficiencies (decolorization) between 98 and 99% were determined, while total organic carbon removal efficiencies were calculated to be in the 53–98% range. Iron leakage investigation showed that iron is lost in higher amounts for the catalysts prepared using the impregnation method by comparison with the pillared sample. Full article