Catalytic Wet Oxidation Research Articles

Catalytic wet oxidation of high concentration formaldehyde wastewater over Pt/nitrogen-doped activated carbon

High concentration formaldehyde (HCHO) wastewater was treated by catalytic wet oxidation (CWO) using Pt/activated carbons. The activated carbons (ACs) with different surface nitrogen content were prepared by H2O2 pre-oxidation and thermal treatment with melamine. The corresponding Pt/ACs were prepared by excess volume impregnation process and characterized by N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The CWO experiments were performed in a co-current upflow fixed bed reactor at 125 °C and 1.0 MPa. The results revealed the positive effect of nitrogen-containing surface groups on the Pt–AC interactions, and resulting in a smaller Pt nanoparticles size and a narrower distribution. Compared with the original Pt/AC, more nitrogen content of Pt/AC showed higher catalytic activity in the mineralization of high concentration formaldehyde (~ 17,000 mg/L) and COD (~ 23,000 mg/L). After 170 h of time on stream, HCHO and COD concentrations of effluent from Pt/AC increased from 482 to 805 mg/L, and from 1895 to 2980 mg/L, respectively, while those from Pt/nitrogen-doped AC just increased from 0.6 to 30.6 mg/L, and from 48 to 345 mg/L even at 350 h of time on stream. Lesser Pt leaching and the extent of agglomeration of Pt NPs were observed over nitrogen-containing Pt/AC. CWO using Pt/nitrogen-doped AC may be applied as a promising treatment for high concentration HCHO wastewater prior to biological system.

Formation of copper hydroxy double salts derived from metal oxides and their catalytic activity in degradation of methyl orange

This work reports the preparation and application of copper hydroxy double salts (Cu-M HDS) as catalysts for degradation of a model wastewater dye pollutant, methyl orange (MO), under ambient conditions. The Cu-M HDS (M = Ca, Zn, La and Pb) were derived in 30 min from hydrothermal treatment of aqueous copper (II) nitrate and the corresponding metal oxide. All Cu-M HDS systems were highly active for catalytic wet oxidation (CWO) of MO, with complete oxidation of 500 ppm MO possible in less than 10 min under ambient (pH 7.0, 30 °C) conditions, with no requirement for additional oxidants. Dissolved oxygen is crucial for activity, as indicated by poor conversions under anaerobic conditions. Decolorization follows first-order kinetics, with catalyst systems having high surface area and Cu content (Cu-Ca HDS, Cu-La HDS) being most rapid. These features, coupled with favorable reusability profiles and ease of fabrication and use, highlight the potential of Cu-M HDS systems in water remediation strategies.

Water-insoluble hybrid materials based on polyoxomolybdate nanoclusters as efficient catalysts

In the current study, we hydrothermally synthesized polyoxomolybdate-based hybrid materials, [Zn(4,4´-bpy)2(H2O)4]3(Mo8O26)2(NH4)2(4,4´-bpy)6 (1) and [(4,4´-H2bpy)2(H2P2Mo5O23)].2H2O (2) based on β-octamolybdate and Strandberg-type structures using 4,4´-bipyridine (4,4´-bpy) ligand. Structure of the obtained materials was investigated by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), FT-IR and inductive coupled plasma optical emission spectroscopy (ICP-OES). The crystals were insoluble in water and employed as catalysts for the catalytic wet air oxidation (CWAO) as well as catalytic wet oxidation (CWO) of Direct Blue 71 (DB) as a representative of a tri-azo dye pollutant under mild conditions. The POM catalysts exhibited good catalytic activity under ambient conditions and could be reused without loss of crystallinity and activity.

Metal-Free Catalytic Wet Oxidation: From Powder to Structured Catalyst Using N-Doped Carbon Nanotubes

This work shows a promising N-doped carbon catalyst for the oxidation of oxalic acid by catalytic wet oxidation, which is able to compete with the traditional noble metal and metal oxide catalysts used in the process. After preliminary studies conducted in batch mode, the catalytic performance of the metal-free carbon nanotubes, both in powder form and supported on a macrostructured carrier (a cordierite monolith), was evaluated under continuous operating conditions. The ability of the N-functionalities to promote activation and chemisorption of oxygen led not only to fast oxalic acid mineralization under batch mode (5 min of reaction to reach full mineralization), but also to good performance under continuous operation (more than 90% conversion of oxalic acid in the steady state, using the powder and around 55% using the catalyst immobilized on a honeycomb cordierite monolith).

A porous activated carbon supported Pt catalyst for the oxidative degradation of poly[(naphthaleneformaldehyde)sulfonate

Abstract Wet catalytic oxidation of sodium poly[(naphthaleneformaldehyde)sulfonate], a hazardous contaminant of wastewater streams from the textiles industry, by hydrogen peroxide under ambient conditions was explored over platinum supported on a porous activated carbon (PAC). Bulk and surface properties of the Pt/PAC catalyst were investigated by XRD, XPS, SEM, TEM, FTIR, EPR and thermogravimetric analysis. The parent PAC, derived from pyrolysis and subsequent activation of rice husks, exhibited significant micro- and mesoporosity, and a high degree of surface oxidation. Incorporation of 1.7 wt% Pt resulted in mesopore blockage, and a corresponding drop in surface area, associated with the formation of large ∼8 nm metallic nanoparticles. Poly[(naphthaleneformaldehyde)sulfonate] oxidative degradation was studied as a function of reactant concentration and solution pH, revealing first order decomposition kinetics and good activity over pH 3–9 at ambient temperature. Electron Paramagnetic Resonance (EPR)-DMPO spin trapping experiments confirm that oxidation of the organic pollutant proceeded via hydroxyl radical generation. The 1.7 wt% Pt/PAC catalyst showed excellent catalyst stability for five consecutive runs over 25 h in a fluidised bed reactor, delivering > 85% removal of 100 mg/L sulfonate with negligible Pt leaching or activity loss, and comparable performance for treatment of a real tannery effluent stream with a COD equivalent of 1860 mg/L.

Synthesis of highly active and stable Al/Zr pillared clay as catalyst for catalytic wet oxidation of phenol

Natural bentonite clay was used in the synthesis of single and mixed oxide Al/Zr pillared clay catalysts by means of ultrasonic treatment during the aging and intercalation steps. The raw bentonite and pillared clay catalysts were characterized using high resolution scanning electron microscopy with energy dispersive system (HRSEM-EDS), powder X-ray diffraction (PXRD), N2 adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, cation exchange capacity, zeta potential and all the catalysts evaluated in the catalytic wet air oxidation (CWAO) of phenol. Calcination of the synthesized Al/Zr-PILCs at 500 °C for 120 min yielded optimum physical properties with BET surface area of 230 m2/g, pore volume of 0.115 cm3/g and basal spacing of 1.92 nm and with good thermal stability. Complete removal of phenol was obtained after 120 min and 88% TOC was removed after 180 min in aqueous solution under mild reaction conditions of 100 °C and 10 bar after. Catalyst reusability studies showed that the Al/Zr-PILCs catalyst demonstrated excellent chemical and structural stability with insignificant leaching of Zr4+ after six consecutive catalytic runs. The Al/Zr-PILCs catalyst therefore demonstrated excellent catalytic properties in the CWAO of phenol in aqueous solution.

Enhanced selective catalytic wet oxidation of H2S to S over Ce–Fe/MgO catalysts at ambient temperature

Abstract In the study we prepare novel MgO supported magnetic Ce–Fe catalysts for selective catalytic wet oxidation of H2S to elemental sulfur at ambient temperature. Characterization of the MgO supported Ce–Fe catalysts and the corresponding catalytic activity for H2S removal were analyzed and evaluated. Compared to the MgO supported Fe catalysts, the Ce incorporation increases significantly catalytic activity for H2S removal due to the oxidation of Fe2+ to Fe3+ improved by the redox couple Ce4+/Ce3+. Besides, we also found that the Ce incorporation reduced sulfates and sulfur deposited on the surface of the catalysts. Under high oxygen atmosphere, contaminants are almost not formed on the surface of the Mg supported Ce–Fe catalysts, extending their lifetime.

Catalytic wet oxidation of high concentration pharmaceutical wastewater with Fe3+ as catalyst.

Catalytic wet oxidation of high concentration pharmaceutical wastewater with Fe3+ as catalyst was carried out in a batch reactor. Results showed that the degradation of pharmaceutical wastewater was enhanced significantly by Fe3+. The effects of reaction parameters, such as the catalyst dose, reaction temperature, time, and initial oxygen pressure, were discussed. The chemical oxygen demand (COD) removal increased with the increases of catalyst dose, temperature, time and oxygen supply. With the initial COD 34,000-35,000 mg/L, approximately 70% COD removal can be achieved under the conditions of catalyst 1.0 g and oxygen pressure 1.0 MPa at 250 °C after 60 min. The results of kinetic studies showed that two reaction steps existed in this oxidation process, which followed an apparent first-order rate law. This process provides an effective approach for the pretreatment of high concentration pharmaceutical wastewater.

A novel catalyst of ceria-nanorods loaded on carbon xerogel for catalytic wet oxidation of methyl green dye

In this study, promising catalysts of ceria nanorods-supported on the porous carbon xerogels via impregnation route were prepared. Three different molar concentrations of ceria catalysts (0.15, 0.25 and 0.50 mol/L) loaded onto carbon xerogels and denoted as follows 0.15Ce/CX, 0.25Ce/CX and 0.50Ce/CX were studied in the catalytic oxidation of methyl green (MG) dye. Nanorods-like shape of the CeO2 supported on the carbon xerogel was determined using both scanning electron microscope (SEM) and transmission electron microscope (TEM). Other techniques such as FTIR, XRD and N2 adsorption–desorption were investigated. The catalytic activity of the obtained samples was examined under various variables such as ceria loading, initial concentrations of dye, H2O2 dose and temperature to optimize the operating conditions. Catalytic wet oxidation experiments revealed that 0.25Ce/CX catalyst has the highest catalytic activity toward degradation of MG dye. The presence of ceria generated a large content of reactive basic oxygen species at the surface of CX and thus enhanced the catalytic oxidation of the pristine CX support. The optimal parameters showing efficient catalytic oxidation toward MG dye found to be 0.25 mol/L cerium loading, 0.139 mol/L H2O2 and temperature of 40 °C at pH 6.0 where 100% degradation of MG dye was obtained within 30 min. The maximum removal of dye through adsorption process only was reached to 54 and 42% onto CX and 0.25Ce/CX at 120 min. Conclusively, the studied catalytic system assessed that there was a synergetic effect as a result of a combination of basic oxygen groups and redox properties of CeO2 at the surface of CX which is effective for a heterogeneous Fenton-catalysis in liquid-phase processes.

Effective treatment of oily scum via catalytic wet persulfate oxidation process activated by Fe2+

Oily scum, a hazardous by-product of petroleum industry, need to be deposed urgently to reduce environmental risks. This paper introduces catalytic wet persulfate oxidation (CWPO) process in the treatment of oily scum to realize risk relief. Under the activation of heat and Fe2+, persulfate (PS) was decomposed into sulfate radicals and hydroxyl radicals, which played a major role on the degradation of petroleum hydrocarbons. The effects of wet air oxidation (WAO) and CWPO process on the degradation of oily scum were compared. In CWPO process, the total petroleum hydrocarbons (TPHs) content of oily scum was decreased from 92.63% to 16.75%, which was still up to 70.19% in WAO process. The degradation rate of TPHs in CWPO process was about 3.38 times higher than that in WAO process. The great performance of CWPO process was also confirmed by elemental analysis, which indicated that the C and H contents of oily scum were reduced significantly by CWPO process. These results indicated that CWPO process has high potential on the degradation of oily scum for environmental protection.

Catalytic Wet Oxidation of Pharmaceutical Sludge by Molecular Sieve Loaded with Cu/Ce

In the present study, the catalytic wet oxidation of pharmaceutical sludge by molecular sieve loaded with Cu/Ce as catalyst was investigated. Experiments were performed in an experimental batch reactor. Reaction parameters including catalyst dose, temperature, time, and oxygen pressure were discussed. The results showed that the catalysts prepared by co-precipitating method have good catalytic performance. Under optimum conditions, the highest volatile suspended solids (VSS) removal rate approximately 92% and chemical oxygen demand (COD) removal rate of 75% were obtained at 260 °C for 60 min with initial oxygen pressure 1.0 MPa and the catalyst 10 g/L. These results implied that the catalytic wet oxidation of pharmaceutical sludge by molecular sieve loaded with Cu/Ce is a promising method for the highly efficient degradation of the sludge.

Green Synthesis of CoFe2O4 and Investigation of its Catalytic Efficiency for Degradation of Dyes in Aqueous Medium

Abstract The catalytic wet oxidation is one the methods used for elimination of dyes from aqueous medium in which various metal based materials can be used as heterogeneous catalysts. Bimetallic oxides as heterogeneous catalysts have gained much attention as bimetallization improve the catalytic properties of the resulting particles. The biosynthetic green method is the most viable and simple method for synthesis of bimetallic oxides nanoparticles. Here, we report the green synthesis of CoFe2O4 particles using Azadirachata indica leaves extract as reducing and stabilizing agent. The synthesized particles were characterized using X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy and scanning electron microscopy. The synthesized CoFe2O4 particles were tested as a catalyst for mineralization of rhodamine B and methylene blue dyes in the presence of hydrogen peroxide in aqueous media. More than 95% dyes degraded in 120 min. The reaction kinetics was described in terms of Langmuir–Hinshelwood mechanism which suggests that molecules of dye and hydrogen peroxide adsorbed surface of CoFe2O4 and then react together.

Catalytic wet oxidation of quinoline over Ru/C catalyst

In the present work, catalytic wet air oxidation of the model nitrogenous organic compound quinoline was studied in a slurry reactor over 5% Ru/C catalyst between 423 and 598 K temperature, 0.34 and 2.07 MPa oxygen (O2) partial pressure, and 0.025 and 0.1 kg m−3 catalyst loading. This catalyst was very effective, thereby suggesting its utility for the oxidative destruction of wastewaters polluted by nitrogenous organic compounds. From analysis of the mass transfer effects, it was found that the investigated reaction belonged to the kinetics-controlled reaction regime. Kinetic data on TOC destruction were fitted to a two-step first-order power law model: the first step was fast, whereas the second step was slow. The values of activation energy for the two steps were 29 and 93 kJ mol−1. Among the hyperbolic models tested, the model with a slow surface reaction between chemisorbed TOC and dissociatively adsorbed O2 was most appropriate. The fate of the nitrogen atom in the feed solution and its conversion to nitrite and nitrate ions, ammonia and nicotinic acid was established. Finally, it was corroborated that the reaction was fast when pyrex liner was used inside the reactor because free radicals were not destroyed by the reactor wall.

Hetero-catalytic hydrothermal oxidation of simulated pulping effluent: Effect of operating parameters and catalyst stability

In the present study, activated carbon (AC) supported bi-metallic catalyst (3.3Cu/2.2Ce/4.4AC) was subjected to catalytic wet oxidation (CWO) of simulated pulping effluent at moderate operating conditions (temperatures = 120–190 °C and oxygen partial pressures = 0.5–1.2 MPa). The oxidation reaction was performed in a high pressure reactor (capacity = 0.7 l) with catalyst concentration of 1–5 g/l for 3 h duration. During CWO at 190 °C temperature and 0.9 MPa oxygen pressure, the chemical oxygen demand (COD), total organic carbon (TOC), lignin and color removals from the wastewater were 79%, 77%, 88% and 89%, respectively, while the wastewater biodegradability was enhanced to 0.52 from an initial value of 0.16. TOC mass balance suggested that nearly 86–97% of the degraded TOC was mineralized whereas copper and cerium leaching from the catalyst were in the range of 1–15% and 0.7–1% with respect to their initial amounts. Metal leaching was reduced with increase in the reaction temperature. Global kinetic rate model was also developed using TOC degradation data and the activation energies of two step (rapid followed by slower TOC removal) CWO reaction were determined as 34.2 kJ/mol and 28.5 kJ/mol, respectively.

Investigation on the removal of H2S from microwave pyrolysis of sewage sludge by an integrated two-stage system.

In this study, an integrated two-stage system, including the in-situ catalytic microwave pyrolysis (ICMP) and subsequent catalytic wet oxidation (CWO) processes, was proposed to remove H2S released from microwave-induced pyrolysis of sewage sludge. The emission profile and H2S removal from the pyrolysis of raw sewage sludge (SS) and sewage sludge spiked with conditioner CaO (SS-CaO) were investigated. The results showed that CaO played a positive role on sulfur fixation during the pyrolysis process. It was found that SS-CaO (10wt.%) contributed to about 35% of H2S removal at the first stage (ICMP process). Additionally, the CWO process was demonstrated to have promising potential for posttreatment of remaining H2S gas. At the Fe3+ concentration of 30g/L, the maximum H2S removal efficiency of 94.8% was obtained for a single Fe3+/Cu2+ solution. Finally, at the pyrolysis temperature of 800°C, 99.7% of H2S was eliminated by the integrated two-stage system meeting the discharge standard of China. Therefore, the integrated two-stage system of ICMP+CWO may provide a promising strategy to remove H2S dramatically for the biomass pyrolysis industry.

Catalytic wet oxidation of aniline over Ru catalysts supported on a modified TiO2

The catalytic wet air oxidation of aniline over Ru catalysts supported on modified TiO2 (TiO2, Ti0.9Ce0.1O2, Ti0.9Zr0.1O2) is investigated. A series of characterization techniques are conducted to determine the relationship between the physico-chemical properties and the catalytic performance. As a result of the good metal dispersion and large number of surface oxygen species, the Ru/Ti0.9Zr0.1O2 catalyst presents the best catalytic activity among the tested samples. The effects of the operating conditions on the reaction are investigated and the optimal reaction conditions are determined. Based on the relationship between the by-products concentration and the reaction time, the reaction path for the catalytic oxidation of aniline is established. Carbonaceous deposits on the surface of the support are known to be the main reason for catalyst deactivation. The catalysts maintain a constant activity even after three consecutive cycles.

Reactivity of novel Ceria–Perovskite composites CeO2- LaMO3 (MCu, Fe) in the catalytic wet peroxidative oxidation of the new emergent pollutant ‘Bisphenol F’: Characterization, kinetic and mechanism studies

In the present study, ceria, pristine perovskites LaMO3 (Cu, Fe) and novel ceria-perovskite composites CeO2-LaMO3 were successfully prepared and applied as heterogeneous Fenton like- catalysts for the degradation and mineralization of a new emergent compound- bisphenol F (BPF) in aqueous solution. The catalysts were characterized by X-ray diffraction spectrometer (XRD), BET surface area determination, scanning electron microscopy (SEM), Energy Dispersive X-ray (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. Catalytic bisphenol F behavior shows that the activity of pristine perovskites was improved due to the introduction of cerium. Catalytic activity in terms of TOC removal followed the order of CeO2-LaCuO3>CeO2-LaFeO3>LaCuO3>LaFeO3>CeO2 with about 83, 79, 68, 64 and 28% respectively. Only the novel composite oxide CeO2-LaCuO3 was found to be effective for Bisphenol F degradation at neutral conditions. EPR analyses and scavenging experiments revealed that BPF was mainly decomposed by the attack of OH, especially the surface-bounded OH. BPF decay followed pseudo-first-order reaction kinetics. The absolute rate constant for BPF oxidation by OH was found to 2.09109M−1s−1, as determined by the competition kinetic method. Six stable organics intermediates were observed and five of them were identified p-benzoquinone, hydroquinone, 4-hydroxybenzaldehyde and Bis (4-hyroxyphenyl) methanol. Subsequent attack of these intermediates by OH radicals led to the formation of short chain acids: malonic, succinic, acetic, formic and oxalic acids. On the basis of the analytical results for the intermediate products and the assumption that hydroxyls radicals are the major reactive species, a plausible pathway of BPF mineralization during the heterogeneous Fenton process was proposed. Furthermore, the CeO2-LaCuO3 composite exhibited excellent long-term stability in the heterogeneous Fenton-like process. These results suggested that the novel ceria perovskite material would be a promising candidate for practical wastewater treatment.

Honeycomb nano cerium oxide fabricated by vacuum drying process with sodium alginate

Nano cerium oxide (CeO2) with honeycomb structure were synthesized simply and rapidly by vacuum drying method with sodium alginate as the biological template agent, Ce(NO3)3·6H2O as cerium source. The composition, aperture size, specific surface area and morphology of the prepared samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 adsorption-desorption and scanning electron microscopy (SEM). Simultaneously, the effects on the morphology of the samples, which were caused by the drying method and the concentration of sodium alginate, were investigated. The results indicate that the prepared samples were nano CeO2 with high crystallinity and uniform dispersion, most of which had mesoporous, macroporous and honeycomb structure. The specific surface area of CeO2 is 210.0 m2/g, and the average aperture is 12.77 nm. The prepared samples can act as catalyst in the catalytic wet oxidation process for the treatment of high concentration organic wastewater, and the COD removal rate could exceed 90%.

Catalytic wet oxidation of chlorinated organics at mild conditions over iron doped nanoceria

Degradation of 4-chlorophenol, 2,4-dichlorophenol and 2,4-dichlorophenoxy acetic acid was investigated by wet air oxidation over CexFe1−xO2 (x: 0, 0.25, 0.5, 0.75, 1) nanocatalysts. Complete removal of target pollutants could be effected at atmospheric pressure and near ambient conditions with considerable decrease in TOC and COD. 4-chlorophenol (1000mg/l) was completely degraded with 59.66% TOC and 84.9% COD removal at 40°C over Ce0.75Fe0.25O2 catalyst whereas 2,4-dichlorophenol (1250mg/l) conversion with 74.3% TOC and 93.62% COD removal was observed at 50°C over Ce0.75Fe0.25O2 catalyst. The activity of the catalysts was found to increase on repeated runs.

Efficient degradation of organic phosphorus in glyphosate wastewater by catalytic wet oxidation using modified activated carbon as a catalyst

ABSTRACTGlyphosate (PMG) wastewater, which is an organic phosphorus (OP) wastewater containing 200–3000 mg/L PMG, was treated via catalytic wet oxidation (CWO) to degrade PMG to orthophosphate (). The catalysts were activated carbons (ACs) modified by H2O2 oxidation and thermal treatment with ammonia or melamine. The catalysts were characterized using N2 adsorption/desorption, Boehm titration, and X-ray photoelectron spectroscopy. The CWO experiments were performed in a co-current upflow fixed-bed reactor at 110–130°C and under 1.0 MPa. The AC modified by H2O2 and melamine had the highest catalytic activity and had excellent stability in the continuous 55-day test: 100% PMG removal and over 93% OP removal for different samples of real PMG wastewater. More pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen along with quinone oxygen functional groups on the surface of the AC showed higher catalytic activity according to linear fitting results. The identification and quantification of critical reaction intermediaries and the main end products of PMG degradation were possible, and a degradation pathway was proposed.