Catalytic Oxidation Research Articles

Innovative Fixed-Bed Reactor Integrated with Heat Transfer System for Lean Methane Mixture Removal

A new type of compact, portable fixed-bed reactor integrated with a heat transfer system was developed for the removal of volatile and flammable air pollutants such as lean methane and volatile organic compounds (VOCs). The reactor may operate in catalytic or thermal combustion conditions with the purpose of achieving autothermal processes with the possibility of energy recovery. An excess heat recovery point was designed behind the reactor bed at the place where the gas temperature is the highest to enable its usage. The mathematical model is presented together with a number of simulation calculations performed for the assessment of the developed reactor. The case study in this paper was for catalytic methane oxidation at a temperature of 400 °C, a methane concentration between 0.1% and 2% by weight, a gas flow rate of 1 m3/s STP, and a heat exchange surface for the assumed plate exchanger from 10 to 200 m2. The calculations show that the thickness of the insulation is of little importance for the operation of the equipment, and a sufficient thickness was about 20–50 mm. The optimal area for the considered case is 80–100 m2. It was found that recovery of thermal energy is possible only for higher methane concentrations, above 0.3% by weight. Using an appropriate surface for the exchanger, it is possible to recover even 50% of the combustion enthalpy at a methane concentration of 0.45% by weight. For an exchanger area below 50 m2, the recoverable energy drops rapidly. It was found that the exchanger area is the most important equipment parameter under consideration.

A colorimetric sensor based on multiple elements doped carbon dot nanozyme for rapid detection of 1-naphthol in human urine samples

The residual carbaryl in crops can cause serious damage to the human kidney and nervous system after entering the human body, which may be metabolized to 1-naphthol (1-NAP) and excreted through urine. 1-NAP is often used as the biomarker for carbaryl exposure, so the intake or leakage of carbaryl can be monitored by detecting the concentration of 1-NAP. Herein, Co, N, P ternary co-doped carbon dots (CoNP-CDs) derived from vitamin B12 were synthesized by a facile hydrothermal method. CoNP-CDs exhibited oxidase-like activity and excellent peroxidase-like activity, which was attributed to the Fenton-like reaction of Co2+/Co3+ and the presence of pyrrole N and P elements, which together provided multiple active sites for chromogenic substrates. Due to the dual enzyme-like activity of CoNP-CDs, hydroxyl radicals (OH) and superoxide radicals (O2−) were generated during the catalytic process, which could rapidly oxidize colorless 3,3′,5,5′-tetramethyl benzidine (TMB) to blue oxidation products (oxTMB). The α-carbon in 1-NAP can be attacked by OH, and the catalytic oxidation process of TMB can be inhibited by the consumption of OH, so that the blue color of the solution became lighter. Based on this principle, a smartphone-assisted colorimetric sensing platform was constructed for the detection of 1-NAP, and which resulted in a linear range of 1.07–37.3 μM and a visual detection limit of 0.68 μM. Moreover, the colorimetric sensing system showed satisfactory recoveries in the detection of human urine samples. The colorimetric sensing system owned the advantages of fast response, strong selectivity and simple operation, and provided a potential strategy for the on-site detection of 1-NAP.

Endogenous iron-enriched biochar loaded nickel-foam cathode in electro-Fenton for ciprofloxacin degradation: performance, mechanism and DFT calculation

Steel mill wastewater sludge, with abundant endogenous iron resources, could be pyrolyzed into iron-enriched biochar (SBC) in one step and loaded onto nickel foam cathode (Ni-Foam) to construct a heterogeneous electro-Fenton system (SBC@Ni-Foam/EF). The purpose of this study were to optimize SBC@Ni-Foam/EF for efficient ciprofloxacin (CIP) removal, and its degradation mechanism and pathway in the presence of endogenous iron were elucidated by DFT calculation. The results showed that the highest CIP degradation efficiency (95.11 %) was achieved at a SBC pyrolysis temperature of 800 °C, an initial solution pH of 3, a Na2SO4 concentration of 0.05 mol L−1, a current density of 40 mA cm−2, and an aeration rate of 200 mL min−1. The degradation of CIP by SBC@Ni-Foam/EF was dominated by cathodic catalytic oxidation, and ·OH played a major role in the CIP degradation process. Combined with characterization and DFT calculation, the endogenous iron was dispersed in the stable Fe3O4 crystalline phase, which provided surface defects and catalytic sites for the cathode and promoted H2O2 activation to generate ·OH through iron cycling. The possible degradation pathways of CIP were proposed to include the cleavage of piperazine and quinolone rings, hydroxylation, and substitution or detachment of fluorine, etc., and the overall toxicity of the intermediates was alleviated after SBC@Ni-Foam/EF treatment. Therefore, this study was expected to achieve a win–win situation for iron-enriched sludge biomass resource utilization and CIP wastewater treatment.

S vacancies and heterojunction modulated MoS2/C@Fe3O4 towards improved full-spectrum photo-Fenton catalysis: Enhanced interfacial charge transfer and NIR absorption

Fe3O4-based core–shell/heterojunction composites exhibit favorable photothermal catalytic performance in environmental remediation, but limited by the weak interface electron transport efficiency and poor near infrared (NIR) absorption capacity. Herein, Sv-MoS2/C@Fe3O4 core–shell composites were prepared for the first time by coating S vacancies-bearing MoS2 (Sv-MoS2) on the surface of carbon-decorated Fe3O4 microspheres (C@Fe3O4) derived from copper slag-based polymer microspheres and was used as photothermal catalyst to activate H2O2 towards chlortethromycin hydrochloride (CTC) elimination from wastewater. By virtue of the synergistic effect of the petal-like Sv-MoS2, carbon-decorated layer and multi light reflection in porous microspheres, Sv-MoS2/C@Fe3O4 exhibited excellent full spectrum absorption and carrier migration efficiency, with catalytic activity of 0.149 min−1 and H2O2 utilization rate of 93.6 %. The degradation rate is 3.9 and 3.1 times of C@Fe3O4 and MoS2/C@Fe3O4 under full light irradiation which can heat the solution from room temperature to 72.4 °C. This excellent catalytic performance is mainly originated from that the S-type heterostructure promotes the charge separation, transfer and redox ability, and enhances catalytic oxidation by regulating electron density of the interfacial carbon and reducing the energy barrier of H2O2 activation through S vacancies. Moreover, the decorated carbon layer can serve as a hot core to provide heat to Sv-MoS2 and enhance the collision chance of photogenerated carriers, thus improving the catalytic performance of Sv-MoS2/C@Fe3O4. This work provides new strategies for constructing heterojunction materials with fast electron transport efficiency and using solar energy for environmental remediation.

Intensified O2 activation and lattice O supply at inverse oxide-metal interface for catalytic oxidation reactions: A case study in alcohol oxidation

Inverse oxide/metal catalysts are recently employed and of great importance in catalytic oxidation reactions, due to the high activity and sintering-resistance. However, the investigations for identification of active-site structure, adsorption-activation of O2, and insight into interface-enhanced mechanism are relatively scare. Herein, the inverse “CoOx-Au” ensemble (∼10 nm CoOx nanoparticles onto ∼30 nm Au particles) for gas-phase alcohol oxidation was exampled to investigate above issues, under the premise of delivering 92 % benzyl alcohol conversion with 98 % benzaldehyde selectivity at 240 °C and atmospheric pressure. It is revealed that O2 is activated at CoOx-Au interface. The “CoO-Au ↔ Co3O4-Au” redox cycle at CoOx-Au interface proceeds over the “CoO↔Co3O4” cycle on CoOx surface, due to the weakened interfacial Co-O bond. And the enhanced redox cycle intensifies O2 activation and lattice O supply. The O2 activation at inverse oxide-metal interface provides promising clue for rational design of inverse catalysts for catalytic oxidation reactions.

Regulating active oxygen species and acidity of Ca doped LaMnO3 perovskite catalysts toward efficient n-butylamine oxidation

It is of great significance to design catalysts with high activity, N2 selectivity and stability for nitrogen-containing volatile organic compound (NVOC) catalytic purification. Meanwhile, the role of oxygen species in NVOC catalytic oxidation is still ambiguous. Herein, the oxygen species of La-Mn perovskite catalysts were engineered by doping Ca in La site to elucidate their role in catalytic n-butylamine oxidation. Results demonstrate that La0.9Ca0.1MnO3 exhibits the highest activity owing to its abundant adsorbed oxygen species and high surface area, achieving 100 % n-butylamine conversion (500 ppm; GHSV=60,000 mL g−1h−1) at 200 °C with N2 selectivity of ca. 95 %. More adsorbed oxygen species generated due to Ca doping accelerates the oxidation rate and C-C cleavage of alcohol and acetate intermediates, resulting in higher CO2 yield. Meanwhile, Ca-doping also modifies the acidity of catalysts, which affects the adsorption/desorption process of alkaline substances and yield of nitrogen-containing products. In addition, La0.9Ca0.1MnO3 shows superior stability, high water and SO2 resistance, and acceptable activity for other common NVOCs, demonstrating a promising catalyst for NVOC oxidation even under harsh operation conditions. Furthermore, the toxic effect of pollutant or products during n-butylamine catalytic oxidation on the growth of Chlorella Vulgaris was investigated and results suggest that catalytic oxidation is an environmentally friendly method for NVOC purification. This work sheds light on the relationships among oxygen species, catalyst acidity, and n-butylamine catalytic oxidation, which expand the understanding of rational design of efficient catalyst for NVOC oxidation.

Optimisation of Catalytic Oxidation Conditions for the 2‐Keto‐L‐Gulonic Acid Production Using Response Surface Methodology

AbstractL‐Ascorbic acid, also known as vitamin C, is a very important antioxidant ingredient situated many usage areas in different industries. 2‐keto‐L‐gulonic acid (2‐KLG) is the main precursor component of L‐ascorbic acid production and it can be produced from L‐sorbose via microbial fermentation or chemical (catalytic) oxidation. While some special strains are used in microbial fermentation, it is benefitted from some catalysts in chemical oxidation. Herein, it was aimed to determine the optimum reaction temperature, pH, and time conditions to produce maximum 2‐KLG compound with the catalytic oxidation of L‐sorbose in the presence of Pt/Al2O3 catalyst with response surface methodology approach. For this aim, the reaction temperature, pH, and time used as variable factors. The limit values of variable factors were applied as 40–60 °C for the temperature, 7.00–9.00 for the pH value, and 3–9 h for the time. The analyses results demonstrated that the increasing temperature and time negatively effected the conversion of L‐sorbose into the 2‐KLG. The optimum conditions of variable factors were determined as 41.30 °C for the temperature, 8.23 for the pH, and 3.25 h for the reaction time by the central composite design. Under these optimum conditions, L‐sorbose was converted into 2‐KLG with an average yield of 43.70 %.

Zinc oxide morphology-dependent CuOx-ZnO interactions and catalysis in CO oxidation and CO2 hydrogenation

CuO/ZnO catalysts with different ZnO morphologies, i.e. nanoplates (p-ZnO) and nanorods (r-ZnO), have been prepared to test for CO oxidation and CO2 hydrogenation. Strong morphology-dependent CuOx-ZnO interactions were observed, which are tightly associated with the ZnO morphology. p-ZnO predominantly exposing polar {002} facets greatly promote the CuOx-ZnO interactions, contributing to the stabilities of CuOx/ZnO catalysts in both reactions. Experimental evidences reveal that CuO-ZnO interfaces act as the active sites in CO oxidation. CuO/p-ZnO catalyst with stronger CuO-ZnO interactions can facilitate the generations of fine CuO and interfacial Cu(I) species, responsible for the adsorption and reactivity of CO and subsequently the high (intrinsic) activity in CO oxidation. However, CuO/ZnO catalysts undergo in situ restructuring to generate Cu/ZnO in CO2 hydrogenation, whose catalytic performance is determined by the key step of CO2 activation. Consequently, Cu/r-ZnO catalyst possessing more surface basic sites exhibits better catalytic performance. These results greatly deepen the fundamental understanding of Cu-based catalysts in both reactions and broaden the concept of morphology-dependent catalysis of oxide-based nanocrystal catalysts that varies with the reactions catalyzed.

Investigation into the role of MoS2 in the composite of Cu-Cu2O/MoS2 in catalytic aerobic oxidation of benzylic alcohols

Cuprous oxide (Cu2O), as a common transition metal semiconductor material, has found extensive applications and research in the field of catalysis due to its unique physicochemical properties. To improve its catalytic performance, introducing carriers to form composite materials with Cu2O has proven to be a promising strategy for enhancing its stability, activity, and selectivity. In this study, we introduced MoS2 to form a composite material with Cu-Cu2O, investigating the impact of MoS2 on the activity of Cu-Cu2O in selective alcohol oxidation. The results demonstrate a significant improvement in the catalytic activity of Cu-Cu2O upon the introduction of MoS2. Further investigations substantiate the close correlation between the enhanced activity of Cu-Cu2O and the interaction with thin layered MoS2 flakes. The quantity of the thin layered MoS2 is small but its impact on the catalytic activity is significant. It induces changes in the band and electronic structures of Cu-Cu2O, and the changes facilitate the activation of O2 and electron transfer in the oxidation, and thus promote the catalysis.

The catalytic decomposition of aqueous rhodamine B using porous carbons and persulfate: Influence of catalytic surface oxidation with ozone

The catalytic decomposition of aqueous rhodamine B using porous carbons and persulfate: Influence of catalytic surface oxidation with ozone

CePO4 supported Cr catalyst with superior sulfur tolerance for selective catalytic oxidation of ammonia

CePO4 supported Cr catalyst with superior sulfur tolerance for selective catalytic oxidation of ammonia

Effect of crown ethers and polyglycols on the catalytic oxidation of cyclohexane and alkylarenes

Effect of crown ethers and polyglycols on the catalytic oxidation of cyclohexane and alkylarenes

Is it possible to realize the catalytic oxidation of toluene on the atomic active site ZnNi/SNC catalysts without external energy?

Volatile organic compounds (VOCs) pose an extremely high risk to both natural environment and human health. The stable conjugated π-bond conformation of aromatic rings make the degradation of aromatic hydrocarbon organic pollutants without relying on external energy remains a great challenge. In this study, toluene was selected as the target pollutant, and constructed sulfur-doped atomic active site catalysts using metal–organic frameworks as precursors. The results showed that ZnNi/SNC-950 could remove toluene up to 99%, with the CO2 selectivity of 12.6%. Ni and Zn were atomically dispersed on the carriers, while S doping modulated the coordination environment of the metal active sites. ZnNi/SNC-950 activates O2 and H2O from the air to produce ·OH, which attacks benzene ring and realizes catalytic oxidation of toluene at room temperature. This work provides a possibility for the degradation of benzene derived VOCs under ambient temperature.

Adenosine triphosphatase synergetic cobalt metal-organic frameworks with enhanced peroxidase-like activity for L-cystine detection

The role of metal–organic frameworks (MOFs) in the field of enzyme-like materials is significant, and they have been successfully applied to various peroxidase-like studies involving catalytic oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB). However, the limited chemical stability of MOFs in aqueous environments hampers their catalytic applications. To address this inherent drawback and enhance the peroxidase-like activity of MOFs, a method involving adenosine triphosphate (ATP) bonding was proposed. In this study, collaborative materials comprising cobalt MOFs (Co-MOFs) and ATP were utilized as model catalysts for TMB catalysis. The presence of ATP significantly improved the catalytic capability of Co-MOFs over a pH range from 3 to 9 and temperatures ranging from 25 to 60 °C. Notably, at pH 7 and 60 °C, the catalytic efficiency increased by approximately 100 times and an impressive enhancement rate of up to 4600 % was achieved respectively. This peroxidase-like catalytic system offers a colorimetric detection assay that selectively detects L-cysteine with a limit of detection as low as 76.2 nM. Incorporating ATP into Co-MOFs presents a novel approach for utilizing MOFs in catalysis that is convenient, straightforward, and gentle.

Reverse Hydrogen Spillover on Metal Oxides for Water-Promoted Catalytic Oxidation Reactions.

Understanding the water-involved mechanism on metal oxide surface and the dynamic interaction of water with active sites is crucial in solving water poisoning in catalytic reactions. Herein, this work solves this problem by designing the water-promoted function of metal oxides in the ethanol oxidation reaction. In situ multimodal spectroscopies unveil that the competitive adsorption of water-dissociated *OH species with O2 at Sn active sites results in water poisoning and the sluggish proton transfer in CoO-SnO2 imparts water-resistant effect. Carbon material as electron donor and proton transport channel optimizes the Co active sites and expedites the reverse hydrogen spillover from CoO to SnO2. The water-promoted function arises from spillover protons facilitating O2 activation on the SnO2 surface, leading to crucial *OOH intermediate formation for catalyzing C-H and C-C cleavage. Consequently, the tailored CoO-C-SnO2 showcases a remarkable 60-fold enhancement in ethanol oxidation reaction compared to bare SnO2 under high-humidity conditions.

Fe-MOFs nanosheets for photo-Fenton degradation of carbamazepine

Iron(II)-based metal organic framework (Fe(II)-MOF) nanosheets have emerged as promising candidates for photo-Fenton catalysis. However, efficiently synthesizing Fe(II)-MOF nanosheets remains a significant challenge. Here, a bottom-up synthesis strategy is proposed to prepare two-dimensional Fe-MOF nanosheets (TFMN) with micrometer lateral dimensions and nanometer thickness, featuring Fe(II) as the metal nodes. The application of TFMN in the photo-Fenton degradation of carbamazepine (CBZ) demonstrates remarkable CBZ degradation performance and excellent efficiency across a wide range of pH values. The electron density and density of states are further calculated by density functional theory. Mechanism analysis identifies h+, •OH and •O2− as the predominant active species contributing to the catalytic oxidation process in the Vis/TFMN/H2O2 system.

Selective recovery of manganese from spent ternary lithium-ion batteries for efficient catalytic oxidation of VOCs: Unveiling the mechanism of activity Enhancement in recycled catalysts

With the widespread application of ternary lithium-ion batteries (TLBs) in various fields, the disposal of spent TLBs has become a globally recognized issue. This study proposes a novel method for reutilizing metal resources from TLBs. Through selective oxidation, manganese in a leaching solution of TLBs was converted into MnO2 with α, γ, and δ crystal phases (referred to as T-MnO2) for catalytic oxidation of volatile organic compounds (VOCs), while efficiently separating manganese from high-value metals such as nickel, cobalt, and lithium, achieving a manganese recovery rate of 99.99%. Compared to similar MnO2 prepared from pure materials, T-MnO2 exhibited superior degradation performance for toluene and chlorobenzene, with T90 decreasing by around 30 °C. The acidic synthesis environment provided by the leaching solution and the doping of trace metals altered the physicochemical properties of T-MnO2, such as increased specific surface area, elevated surface manganese valence, and improved redox performance and oxygen vacancy properties, enhancing its catalytic oxidation capacity. Furthermore, the degradation pathway of toluene on T-γ-MnO2 was inferred using thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and in-situ DRIFTs. This study provides a novel approach for recycling spent TLBs and treating VOCs catalytically.

One-step synthesis of Pt@(CrMnFeCoNi)3O4 high entropy oxide catalysts through flame spray pyrolysis

High entropy oxides (HEOs) show great prospects in catalysis owing to their widely tunable component structures and ease of combination with active metals. However, the development of HEO catalysts is limited by the lack of efficient synthesis methods due to the difficulty of homogeneously mixing at least five elements. In this work, flame spray pyrolysis (FSP) is successfully employed to synthesize (CrMnFeCoNi)3O4 HEO with a single phase spinel structure in one step, which is verified by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDS). Taking CO catalytic oxidation as a probe reaction, the Pt@(CrMnFeCoNi)3O4 HEO catalyst synthesized by FSP in one step is compared with the catalyst whose Pt is impregnated on (CrMnFeCoNi)3O4 HEO support. The FSP-made catalysts have a higher catalytic reaction rate and better redox ability, which lowers the temperature of complete CO conversion by nearly 100 °C. Furthermore, it can be observed that the flame parameters can be optimized to modify the particle size and oxygen vacancies of the HEO nanoparticles, thus enhancing the catalytic performances. This work demonstrates that FSP is an effective method for the one-step synthesis of HEO catalysts with excellent catalytic performance, providing a new perspective for the synthesis of HEO-based materials.

Geometrical features, stability and electronic properties of (Cu3Sn)n clusters

Recently, significant advancements have been made in low-entropy Cu3Sn catalysts, showcasing their efficient catalytic CO oxidation capabilities. Hence, the atomic models of the Cu3Sn are worth established to further investigate their catalytic mechanisms. Here, the structural features and stability of (Cu3Sn)n clusters (n = 1–6) are investigated using the genetic algorithm combined with the density functional theory (DFT). The results reveal the structural evolution of these clusters from hollow cages to compact icosahedrons, where Cu atoms predominantly tend to grow together, while Sn atoms are dispersed at the edge positions. The Eb, Ef and Δ2E analyses show that the icosahedral (Cu3Sn)3 has a higher stability than that of its neighbors. The molecular dynamics simulations demonstrates its stability even at 1000 K. The molecular orbitals and density of states reveal that the (Cu3Sn)3 has an 1S21P61D102S21F1 superatomic electronic configuration. Electrostatic potential surfaces show that (Cu3Sn)n clusters have significant σ-hole regions at the Cu atomic sites, which can make the CO stretching frequency and bond length have a large red-shift. Moreover, the adsorption energy between the (Cu3Sn)3 and CO is the largest, reaching 1.17 eV. Our work provides inferences to the structural characteristics and adsorptions of the CuSn alloys at the atomic level.

Additional research into arsenic (III) effective catalytic oxidation in an aqueous solution on a new calcium doped active manganese dioxide in a flow column

Additional research into arsenic (III) effective catalytic oxidation in an aqueous solution on a new calcium doped active manganese dioxide in a flow column