Catalytic Air Oxidation Research Articles

Catalytic air oxidation of biogas slurry using Cu sub-nanocluster supported by mesoporous TiZrO4 and protected by SiO2 shell

Biogas slurry, an inevitable outcome of anaerobic digestion (AD), is a treatment burden for urban environmental management. In this study, two kinds of biogas slurry (slurry J and slurry C), collected from the AD plants in Japan and China, were treated using novel TiZrO4 @Cu and TiZrO4 @Cu@SiO2 multilayered hollow spheres containing Cu sub-nanoclusters as the catalyst. The results showed that the chemical oxygen demand (COD) was removed by 63 % for slurry J and 44 % for slurry C after 5 h. The Cu sub-nanoclusters acted as co-catalysts and active centers, facilitating rapid electron transfer to oxygen molecules and forming highly reactive •O2− and •OH species (Use slurry J as the based solution). These free radicals cleaved the interconnecting bonds between benzene rings, disintegrated the ring structure, formed intermediate compounds such as n-hexylic acid, and ultimately mineralized organic pollutants in biogas slurry into CO2 and H2O. At the same time, TiZrO4 @Cu@SiO2 had excellent stability due to the protection of the SiO2 shell and reduced threefold Cu leaching than TiZrO4 @Cu. The COD removal rate was always 60 % in six cycles in the slurry J. The new catalyst ensured the high performance of catalytic air oxidation at low temperatures, which has significant potential as an environmentally friendly and energy-saving method for organic wastewater treatment.

Atomically dispersed copper sites on titanium zirconium oxide accelerate the simultaneous oxidative removal of organic carbon and ammonia from landfill leachate

Landfill leachate is a refractory wastewater. Low-temperature catalytic air oxidation (LTCAO) has shown considerable potential for leachate treatment owing to its green and simple operation, but the simultaneous removal of chemical oxygen demand (COD) and ammonia from leachate remains challenging. Herein, TiZrO4 @CuSA hollow spheres with high-loading single-atom Cu were synthesized using isovolumic vacuum impregnation and co-calcination methods, and the catalyst was applied to the LTCAO treatment of real leachate. Consequently, the removal rate of UV254 reached 66% at 90 °C within 5 h, while that for COD was 88%. Simultaneously, the NH3/NH4+ (33.5 mg/L, 100 wt%) in the leachate was oxidized to N2 (88.2 wt%), NO2--N (11.0 wt%), and NO3--N (0.3 wt%) owing to the effect of free radicals. The single-atom Cu co-catalyst in TiZrO4 @CuSA exhibited a localized surface plasmon resonance effect at the active center, which could quickly transfer electrons to O2 in water to form O2.− with a high activation efficiency. The degradation products were determined and the deduced pathway was as follows: the bonds joining benzene rings were first broken, and then the ring structure was further opened to produce acetic acid and other simple organic macromolecules, which were finally mineralized to CO2 and H2O.

Remove humic acid from water quickly using only oxygen and sulfite at nickel cobalt spinel catalyst

The typical refractory organic pollutant, humic acid (HA), causes many water and wastewater treatment obstacles. In this study, a novel method was proposed to degrade HA based on the low-temperature (<100 °C) catalytic air oxidation technology (LTCAO) using the NiCo-spinel (NCO) as a catalyst and the sulfite as a promoter. Sulfite enhanced the quantity of mineralized HA to 2.4 times that without sulfite assistance, and the removal rate of total organic carbon reached 93.1% within 60 min at 90 °C. HA gradually degrades into small organic molecules and is mineralized through interfacial reactions and radical paths. Sulfite plays a triple role in these reactions. Sulfite sulfonated HA destroyed its pseudomicellar structure, making HA easily oxidized. Sulfite also coordinated with NCO and promoted the internal electronic hopping conduction of NCO because of the fast electron transfer between SO32− and the h+sites, thus accelerating the electron transfer between HA and O2 mediated by NCO. In addition, the coordinated SO32− was activated to form the radical ∙SO3−, which strengthened the oxidation of HA. This study supports a simple and green method for efficiently cleaning water and wastewater rich in HA.

Mineralize complex organic contaminants using only oxygen on dense copper atoms embedded in the walls of carbon nanotubes

In this study, a novel catalytic air oxidation (CAO) process is proposed based on a facilely synthesized nanocomposite catalyst. The catalyst was prepared using Cu single atoms (CuSA) embedded on multiwalled carbon nanotubes (CNTs), denoted as CNTs@CuSA, with mass ratio of CuSA up to 10.02 %. Humic acid (HA) and other typical refractory contaminents were used to investigate the ability of CNTs@CuSA in CAO. The catalysts were pre-excited to cross the energy barrier at 120 °C for 10 min, and then used to catalyze the oxidation of HA at 90 °C in 50 min. The CNTs@CuSA with CuSA mass ratio 8.39 % showed a superior catalytic activity, and 99 % of HA in solution was degraded with 98 % of organic carbon mineralization. Aberration-corrected transmission electron microscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations were applied to detect the mechanism. The results showed that the Cu-N coordination sites on CNT walls and the confinement effect of CNTs activated O2 to produce ·OH radicals, with a high activation efficiency. Moreover, this catalyst remained active after multiple cycles. This result provides a new catalyst to support low-temperature catalytic air oxidation for organic wastewater treatment.

Low-temperature degradation of humic acid via titanium zirconium oxide@copper single-atom activating oxygen: Mechanism and pathways

Humic acid (HA), a refractory organic pollutant, has always been a key obstackle in wastewater treatment (such as biochemical landfill leachate). And catalytic air oxidation is one of the most promising methods to degrade HA efficiently and economically. In this study, a novel high-loading Cu single-atom catalyst (TiZrO4@CuSA) was facilely synthesized using isovolume vacuum impregnation and co-calcination method, and then used to accelerate the oxidation of HA at low temperatures. The TiZrO4@5%CuSA catalytic system showed a superior performance, and 91 % of HA was degraded and 90 % of organic carbon was removed from HA solution within 10 min at 90 °C. Aberration-corrected electron microscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations were applied to reveal the catalytic mechanism of TiZrO 4@5%CuSA. The active center of Cu single-atom co-catalyst with Cu − O coordination sites can quickly transfer electrons to O2 in the water to form O2.−, exhibiting high activation efficiency. Gas chromatography (GC), liquid chromatograph-mass spectrometer (LC-MS), liquid chromatography-organic carbon detection (LC-OCD), and Fourier-transform infrared spectroscopy (FT-IR) spectroscopy provided the results of intermediate products, including 3-phenoxy-benzaldehy, phenylglyoxal, ethanol, acetic acid, butyric acid, and valeric acid, and thus a catalytic degradation pathway of HA was speculated. Based on the new catalyst, a new process can be conceived for efficient and economic removal of HA from HA-containing wastewater.

Strengthen Air Oxidation of Refractory Humic Acid Using Reductively Etched Nickel-Cobalt Spinel Catalyst

Nickel-cobalt spinel catalyst (NCO) is a promising catalyst for air oxidation of humic acid, which is a typical natural refractory organic matter and a precursor of toxic disinfection by-products. In this study, reductive etchers, NaBH4 or Na2SO3, were used to adjust the NCO surface structure to increase the performance. The modified catalyst (NCO-R) was characterized, and the relationship between its intrinsic properties and catalytic paths was discovered. The results of O2-temperature programmed desorption, NH3-temperature programmed desorption, and X-ray photoelectron spectroscopy (XPS) demonstrated that reductant etching introduced oxygen vacancies to the surface of NCO and increased active surface oxygen species and surface acidity. In addition, the modification did not change the raw hollow sphere structure of NCO. The crystallinity and specific surface area of NCO-R increased, and average pore size of NCO-R decreased. XPS results showed that the ratio of Co3+/Co2+ in NCO-R decreased compared with NCO, while the ratio of Ni3+/Ni2+ increased. The results of H2-temperature programmed reduction showed that the H2 reduction ability of NCO-R was stronger. Due to these changes in chemical and physical properties, NCO-R exhibited much better catalytic performance than NCO. In the catalytic air oxidation of humic acid at 25 °C, the total organic carbon (TOC) removal rate increased significantly from 44.4% using NCO to 77.0% using NCO-R. TOC concentration of humic acid decreased by 90.0% after 12 h in the catalytic air oxidation using NCO-R at 90 °C.

Photo-induced oxidative cleavage of C-C double bonds for the synthesis of biaryl methanone via CeCl3 catalysis.

A Ce-catalyzed strategy is developed to produce biaryl methanones via photooxidative cleavage of C-C double bonds at room temperature. This reaction is performed under air and demonstrates high activity as well as functional group tolerance. A synergistic Ce/ROH catalytic mechanism is also proposed based on the experimental observations. This protocol should be the first successful Ce-catalyzed photooxidation reaction of olefins with air as the oxidant, which would provide inspiration for the development of novel Ce-catalyzed photochemical synthesis processes.

Catalytic Air Oxidation of Refractory Organics in Wastewater

Catalytic air oxidation (CAO) is an economical, environmentally friendly, and efficient technology used to treat wastewater that contains refractory organics. This review analyzes recent studies regarding five common types of CAO that use external energy sources (heat, light radiation, microwave, and electricity) or non-oxidizing chemical promoters (nitrites and sulfites). Methods include hydrothermal, electro-assisted, photocatalytic, microwave-assisted, and non-oxidizing chemical-assisted CAO. The associated catalytic mechanisms are discussed in detail in order to explain the connections between CAO catalytic pathways. Mechanisms include O2 activation via excitation, free-radical autocatalytic reactions, and coordination catalysis. Classical kinetic mechanisms, including Mars-van Krevelen and Langmuir-Hinshelwood, are also proposed to reveal overall CAO dynamic processes. The catalysts used in each CAO technology are summarized, with a focus on their catalytic pathways and the methods by which they might be improved. Finally, important challenges and research directions are proposed. The proposals focus on further research regarding catalyst mechanisms, mechanism-guided catalyst design, and process improvement.

Catalytic behaviors of manganese oxides in electro-assisted catalytic air oxidation reaction: Influence of structural properties

The electro-assisted catalytic wet air oxidation (ECWAO) process is effective for pollutants removal, by taking advantage of an anodic electric field to activate O2 on a catalyst surface. Herein, three different manganese oxides, including MnO2, Mn3O4 and MnO, are fabricated on graphite felt (GF) support to serve as the catalysts of ECWAO reaction. Structural properties of these manganese oxides are analyzed, and their catalytic behaviors in ECWAO reaction are investigated with bisphenol A as a probe pollutant. The manganese centers on the surface of manganese oxides are found to be present in multi-valence states, favoring the formation of chemisorbed oxygen species which are responsible for pollutants oxidation in the ECWAO process. Therefore, the manganese oxides demonstrate good and stable activity for catalytic oxidation of bisphenol A under room condition. The sequence of their catalytic activities is as follows: Mn3O4 > MnO > MnO2, depending on their low-temperature reducibility and oxygen mobility in them. These results illustrate a guideline to the design of highly active manganese oxide catalysts for the ECWAO reaction.

Solution Catalytic Cycle of Incompatible Steps for Ambient Air Oxidation of Methane to Methanol.

Direct chemical synthesis from methane and air under ambient conditions is attractive yet challenging. Low-valent organometallic compounds are known to activate methane, but their electron-rich nature seems incompatible with O2 and prevents catalytic air oxidation. We report selective oxidation of methane to methanol with an O2-sensitive metalloradical as the catalyst and air as the oxidant at room temperature and ambient pressure. The incompatibility between C–H activation and O2 oxidation is reconciled by electrochemistry and nanomaterials, with which a concentration gradient of O2 within the nanowire array spatially segregated incompatible steps in the catalytic cycle. An unexpected 220 000-fold increase of the apparent reaction rate constants within the nanowire array leads to a turnover number up to 52 000 within 24 h. The synergy between nanomaterials and organometallic chemistry warrants a new catalytic route for CH4 functionalization.

Air oxidation of pollutants on cathodic nickel@nickel oxide/graphite felt under room condition

Oxygen in air is an eco-friendly and economical oxidant, and catalytic air oxidation technology have a great potential to sustain effective wastewater treatment. Here we report a novel cathodic air oxidation process under the catalysis of a nickel@nickel oxide composite loaded on a porous graphite felt. Such a process demonstrates extensive and stable effectiveness in oxidizing a variety of dyes, pharmaceuticals and personal care products at high mineralization efficiencies under room condition. Mechanistic study indicates organic pollutants are oxidized by oxygen at cathodic nickel@nickel oxide/graphite felt through a non-free radical pathway, in which oxygen atom is transferred from oxygen molecule to organic molecules via lattice oxygen species in nickel oxide. The nickel oxide is reduced in the cathodic electric field, liberating and activating lattice oxygen species as the oxidizer of organic pollutants. Then, oxygen re-oxidizes nickel into nickel oxide to replenish lattice oxygen species. Such an oxygen activation pattern through nickel/nickel oxide redox cycle enables pollutant degradation at low energy cost, thus endowing the cathodic air oxidation process with a great potential in practical wastewater treatment.

Novel-structured Mo-Cu-Fe-O composite for catalytic air oxidation of dye-containing wastewater under ambient temperature and pressure

AbstractA novel-structured Mo-Cu-Fe-O composite was successfully prepared by co-precipitation and impregnation method. The properties of the as-prepared samples were determined using X-ray diffraction, temperature-programmed reduction by H2, cyclic voltammetry, and temperature-programmed desorption by O2. The results showed that Mo6+ diffused into the Cu-Fe-O crystal lattice and then formed a new crystalline phase of CuMoO4. The Mo-Cu-Fe-O catalyst had redox properties, and its surface contained active sites for oxygen adsorption. In addition, the catalytic activity of the Mo-Cu-Fe-O composite was evaluated by the degradation of Cationic Red GTL, Crystal Violet, and Acid Red in catalytic wet air oxidation (CWAO) at ambient temperature and pressure. The Mo-Cu-Fe-O catalyst showed excellent activity at basic conditions for the degradation of Cationic Red GTL. High removal efficiencies of 91.5% and 92.8% were achieved for Cationic Red GTL and Crystal Violet, respectively, in wastewater, and the efficiency remained high after seven cycles. However, almost no degradation of Acid Red occurred in the CWAO process. Furthermore, hydroxyl radicals were formed in the CWAO process, which induced the decomposition of the two cationic dyes in wastewater, and the toxicity of their effluents was decreased after degradation. The results indicate that the Mo-Cu-Fe-O composite shows excellent catalytic activity for the treatment of wastewater contaminated with cationic dyes.

Oxidation Kinetics of Propane-Air Mixture over NiCo2O4 Catalyst Emitted from LPG Vehicles

This paper describes the kinetics of catalytic air oxidation of propane. The kinetics data were collected in a plug flow tubular reactor. The experiments were performed over the NiCo2O4 catalyst prepared by co-precipitation method followed by calcination at 400 oC. The kinetic data were collected under the following conditions: 200 mg of catalyst, 2.5 % of propane in air, total flow rate of 60 mL/min, and temperature ranges of 130-170 oC. The data were fitted to the power law rate equation. The activation energy and frequency factor were found to be 59.3 kJ/g mol and 2.9×108 (mol)0.47.L0.53/g cat.h, respectively.

Kinetics of catalytic oxidation of carbon monoxide over CuMnAgOx catalyst

The CuMnAgOx catalyst was prepared by the deposition-precipitation method and followed by calcination at 300°C, which showed excellent activity and stability for carbon monoxide (CO) oxidation at low temperature. This paper describes the kinetics of catalytic air oxidation of CO over the CuMnAgOx catalyst and their kinetics data were collected in a plug flow tubular reactor. The data were collected under the following reaction conditions: 100mg catalyst, 2.5% CO in air, total flow rate maintained 60ml/min and temperature range 25–30°C. The CO oxidation followed in a different reaction mechanism at a broad range of experimental temperature. A better tool for measuring the performance of CuMnAgOx catalyst for CO oxidation is the activation energy for the process and it’s used for the modeling and design of the catalytic converter. The data were fitted into the power law rate equation. The frequency factor and activation energy were found to be 2.7790×105 (gmol)/(gcath) and 16.977kJ/gmol, respectively.

Exploring possible reaction pathways for the o-atom transfer reactions to unsaturated substrates catalyzed by a [Ni-NO2 ] ↔ [Ni-NO] redox couple using DFT methods.

The (nitro)(N-methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO2 )(S2 CNHMe)(PMe3 )] complex catalyses efficiently the O-atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO2 )(S2 CNHMe)(PMe3 )] ↔ Ni(NO2 )(S2 CNHMe)(PMe3 ) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five-member metallacycle intermediate, via a [3 + 2] cyclo-addition reaction of HC≡CH to the Ni-N = O moiety of the Ni(NO2 )(S2 CNHMe)(PMe3 )] complex, followed by a β H-atom migration toward the Cα carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( κN1-NO2 )(S2 CNHMe)(PMe3 )] ⇌ [Ni( κO,O2-ONO)(S2 CNHMe)(PMe3 )] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc.

Gas-liquid reaction and mass transfer in microstructured coiled flow inverter

Microstructured coiled flow inverter (MCFI) as a helically coiled tubular device with 90° alternating bends provides enhanced radial mixing due to secondary flow (Dean vortices) in different planes. Liquid-liquid mass transfer characterization in MCFI revealed higher mass transfer rates compared to other capillary setups. However, the influence of Dean vortices and 90° bends on gas-liquid mass transfer has not been investigated and described yet. Different reactor setups, i.e. MCFI, straight capillary, helical coil, and bend reactor were fabricated from FEP tubes (ID=1mm). Gas-liquid mass transfer performance was investigated for a gas-liquid reaction system, i.e. cobalt (II) catalyzed air oxidation of sodium sulfite. Two-phase slug flow hydrodynamics and pressure drop were experimentally characterized, while the influence of operating and geometrical reactor parameters on conversion was investigated for reactor setups. MCFI offers up to 14% higher conversion in comparison to other capillary setups. Mixing within the liquid phase is enhanced by the formation of Dean vortices and additional direction change via 90° bends, which contribute to the internal diffusion in the liquid phase.

Poly(o-aminophenol) prepared by Cu(ii) catalyzed air oxidation and its use as a bio-sensing architecture

A novel procedure for the preparation of organosoluble poly(o-aminophenol) is described.

Regeneration of spent caustic of olefin unit in a bubble column reactor: Treatment and recovery optimization

In this work, regeneration of spent caustic of olefin unit was investigated. Sulfur compounds in the petrochemical products lead to environmental issues, so they should be eliminated. The strong alkaline media such as caustic is used to remove these compounds. Spent caustic contains noxious components such as phenol, mercaptans, mercaptide, sulfide and high chemical oxygen demand (COD) value of up to 30,000 mg/L. The main purposes are treatment of wastewater and recovery of caustic. The process was carried out in a batch bubble column reactor, and then effluent was treated in a precipitation stirred tank reactor. The catalytic air oxidation was used for treating this waste via IVKAZ catalyst, and lime was applied to sedimentary reactions in second reactor. The full factorial method was used for experimental design along with the RSM method for optimization of experiment results. Three independent variables of temperature, reaction time, and air flow were considered. The results indicate that this method is able to use two different processes (catalytic oxidation and chemical precipitation), due to the fact that the amount of caustic can be increased up to six times of initial value and also could treat solution more than 50%. The optimum conditions are 90°C, 7 L/min, and 30 min, which can be reached by 6% wt caustic, around 5000 mg/L concentration of COD, and 360 mg/L amount of S2− with this newly developed process. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 341–347, 2017

Copper-Induced Inactivation of Camel Liver Glutathione S-Transferase.

Glutathione S-transferases (GSTs) are multifunctional enzymes and play an important role in detoxification of xenobiotics and protection against oxidative stress. Camel liver glutathione transferase (cGST) was recently isolated and characterized in our lab. In this study, we have evaluated the effect of monovalent, divalent, and trivalent cations on its activity and stability. Cu(++) was found to be the potent inhibitor of GST activity which loses complete activity at 0.5-mM concentration. Other metal ions did not inhibit GST even at higher concentration of 2 mM. GST incubated with Cu(++) (0.1 mM) resulted decrease in free sulfhydryl groups by 55%, whereas other metal ions did not show any effect on free thiol content. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed formation of GST aggregates instantly in the presence of Cu(++), which further increased in molecular size with increase in time of incubation. DTT treatment resulted in de-aggregation of GST oligomers to its monomeric form. However, the GST activity was not recovered completely after de-aggregation. Cu(++) was found to inhibit GST activity by accelerating the inter- and intra-disulfide bond formation. Far-UV circular dichroism (CD) results showed that Cu(++)-catalyzed air oxidation of sulfhydryl groups leads to minor conformational changes in the GST.

Polymerization of Aniline in Microemulsion by Catalytic Air Oxidation

SummaryA copper catalyzed air oxidation process is presented for polymerization of aniline in a microemulsion constituting with cetyltrimethylammonium chloride (CTAC) and n‐butanol. The process was demonstrated to give stable and pitch‐dark emulsions of Emeraldine base in molecular weights of 33800 Da, as inferred from the capillary viscometer. A fairly linear viscosity‐conversion relation was noted in each case up to 95.0% of conversion. Differential light scattering (DLS) measurements showed 70 nm of average particle size for the polyaniline (PANI) in the emulsion. Conductivities measured by four‐ point probe technique indicated conductivities 8.3×10−8 and 9.8 Scm−1 for un‐doped and doped PANI.