Catalytic Oxidation Reactions Research Articles

Well-Defined Microenvironment in Metal–Organic Frameworks Enable Green, Benign, and Isolation-Free Catalytic Oxidation Reaction

Well-Defined Microenvironment in Metal–Organic Frameworks Enable Green, Benign, and Isolation-Free Catalytic Oxidation Reaction

Synergetic Effect of Heterojunction and Sulfur Vacancy on ZnIn2S4/CeO2 to Enhance the Photocatalytic Performance of 5‐Hydroxymethylfurfural into 2,5‐Diformylfuran

AbstractThe efficient separation of photocarriers and facile generation of superoxide radicals are crucial for enhancing the performance of photocatalysts in the selectively photo‐oxidizing 5‐hydroxymethylfurfural (HMF) into 2,5‐diformylfuran (DFF). Herein, a ZnIn2S4/CeO2 composite with S‐scheme heterojunction and sulfur vacancies (SV) is successfully developed through a one‐step hydrothermal method. The optimal catalyst (SV‐ZnIn2S4/CeO2) exhibits excellent catalytic activity with 100% conversion of HMF and 96.1% selectivity of DFF in 80 min under ambient conditions, the production rate of DFF is up to 952.6 µmol g−1 h−1. Intriguingly, the performance remains significant even when the concentration of HMF is increased from 8 to 100 mм. Experimental and theoretical investigations discover that the synergistic effect of S‐scheme heterojunction and sulfur vacancies contribute to the separation of photocarriers and the activation of oxygen, which facilitate the generation of superoxide radicals, thus boosting the catalytic oxidation reactions.

Photooxidation of Toluene Derivatives under HAT and ROS Synergy.

The valorization of toluene offers a dual solution by addressing its environmental impact while also facilitating the synthesis of a diverse array of valuable fine chemicals and pharmaceutical intermediates, thus ensuring both ecological sustainability and economic viability. We report herein a synergistic approach that harmonizes hydrogen atom transfer (HAT) process with the generation of reactive oxygen species (ROS) under mild condition and low catalyst loading, which enables the efficient synthesis of a broad spectrum of esteemed benzoic acid derivatives and aryl ketones through the photocatalytic oxidation of toluene derivatives. Mechanistic elucidation reveals that the HAT reagent anthraquinone has both the capabilities to abstract hydrogen atoms and the ability to generate singlet oxygen 1O2 during energy transfer with triplet oxygen 3O2, and the combination of these two potencies significantly improves the catalytic efficiency of the reaction. This study not only introduces the amalgamation of HAT with ROS generation but also delineates a systematic approach for the selection of HAT reagents with energy transfer proficiency for ROS generation in catalytic oxidation reactions.

Exploration of catalytic activities of Caesalpinia bonduc (L.) Roxb. ash on green-oxidation of small organic substrates: an effective way to reduce the use of harsh chemicals

In this modern era, large-scale industrial use of harsh chemicals is an alarming problem as it can cause serious environmental damage. Among industrial pollutants, harsh chemical oxidizing agents are one of the leading chemicals that can cause severe environmental threats. These harmful harsh chemicals are practically omnipresent in industries and are used to oxidize numerous small organic substrates. Replacement of these harsh chemicals with some plant-based products might be helpful to safeguard our environmental damage. In this study, Caesalpinia bonduc (L.) Roxb. ash is used as a catalyst to activate aerial oxygen for promoting the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) and o-aminophenol (OAPH) like small organic substrates. Detailed kinetic studies for these catalytic oxidation reactions have been performed spectrophotometrically, which confirms that catalytic reactions follow Michaelis–Menten kinetics. Several enzyme-kinetics plots such as the Michaelis–Menten plot, Lineweaver–Burk plot, Hanes–Woolf plot, and Eadie–Hofstee plot have been used to determine the maximum rate achieved by the reaction (Vmax) and Michaelis constant (KM) like kinetic parameters. The average values of Vmax and KM for catalytic oxidation of 3,5-DTBC are (8.6669 ± 0.6519) × 10–5 M S−1 and (21.4289 ± 0.4741) × 10–4 M, respectively. Similarly, the average values of Vmax and KM for catalytic oxidation of OAPH are (2.1781 ± 0.2071) × 10–5 M S−1 and (20.1062 ± 1.2690) × 10–3 M, respectively. The mineral composition of Caesalpinia bonduc (L.) Roxb. ash has also been evaluated by using inductively coupled plasma optical emission spectroscopy (ICP-OES).Graphical

Quantification measurement of hemoglobin with large dynamic range and low detection limit via an optical fiber optofluidic laser with enzyme-catalyzed reaction

Quantitative measurement of hemoglobin (Hb) levels is an essential part of routine medical examinations, disease diagnosis and health status monitoring. In this study, we introduced optical fiber optofluidic laser (FOFL) technology combined with catalytic oxidation reaction to design a laser sensor for sensitive Hb detection. For the H2O2-rhodamine B (RhB) oxidation system, radially emitting FOFL was achieved with a thin-walled hollow optical fiber (HOF) as an optical microcavity and amplified the concentration change of RhB during oxidation by H2O2. Hb was employed as peroxide-mimicking enzyme to catalyze the oxidation system, which sped up the reaction, resulting in an earlier laser extinction time. With the laser extinction time as sensing signal, the Hb sensor achieved a dynamic range of five orders of magnitude and a limit of detection (LOD) of 46.0 pM at an assay time of 40 min. The developed method provides ideas for the exploitation of FOFL biosensing based on catalytic oxidation reactions.

Spin-dependent activity of cobalt contained hydroxy double perovskite for efficient antibiotic removal via peroxymonosulfate activation

Cobalt-containing catalysts exhibit good performance in the advancement of efficient catalytic oxidation reactions. However, achieving an optimal balance between reaction kinetics and adsorption, usually governed by variable spin states of Co ions, to enhance the performance remains a significant challenge. This study aims to develop a convenient compositional tuning strategy to achieve such balance in stable CoxZn1-xSn(OH)6 perovskite hydroxides. We systematically investigate the effect of varying spin state on a chosen representative catalytic oxidation reaction, namely peroxymonosulfate activation and tetracycline hydrochloride removal. The magnetic properties analysis reveal that the content of octahedral Co2+ ions with high-spin state increases with Co content (x) and reaches 59.5 % in Co0.5Zn0.5Sn(OH)6. Experimental results and DFT calculations reveal that the spin states transition of Co2+ ions enhance the interaction between Co and O atoms. This enhanced interaction not only improves the reactivity due to the formation of highly covalent Co-OH bonds that serve as catalytically activated charge transfer channels, but also optimizes the suitable adsorption energy of PMS molecules at −3.52 eV for Co0.5Zn0.5Sn(OH)6. Consequently, Co0.5Zn0.5Sn(OH)6 shows superior catalytic activity, achieving nearly 100 % antibiotic removal efficiency within just 10 min, surpassing previously reported catalysts. These findings underscore the potential of compositional tuning spin states of transition metal ions in advancing oxidation processes and designing innovative catalysts.

Star-Like Polypeptides as Simplified Analogues of Horseradish Peroxidase (HRP) Metalloenzymes.

Peroxidases, like horseradish peroxidase (HRP), are heme metalloenzymes that are powerful biocatalysts for various oxidation reactions. By using simple grafting-from approach, ring-opening polymerization (ROP), and manganese porphyrins, star-shaped polypeptides analogues of HRP capable of catalyzing oxidation reactions with H2O2 is successfully prepared. Like their protein model, these simplified analogues show interesting Michaelis-Menten constant (KM) in the mM range for the oxidant. Interestingly, the polymer structures are more resistant to denaturation (heat, proteolysis and oxidant concentration) than HRP, opening up interesting prospects for their use in catalysis or in biosensing devices.

Quantitative Analysis of Catalytic Oxidation Reactions in Oxygen Carrier Aided Fluidized Bed Combustion

Quantitative Analysis of Catalytic Oxidation Reactions in Oxygen Carrier Aided Fluidized Bed Combustion

Mathematical modelling of a self-oscillating catalytic reaction in a flow reactor

The article is devoted to the analysis of possible spatiotemporal kinetic structures that can arise during catalytic oxidation reactions on metal surfaces at atmospheric pressure. The catalytic oscillatory reaction in a flow reactor is modeled using a 1D system of equations of the reaction–diffusion–convection type. The STM type oscillatory reaction model of catalytic oxidation is used as a kinetic model. The obtained results of mathematical modelling show the decisive influence of an axial mixing in the reactor on the development of spatiotemporal structures. It is also shown that, depending on the ratio of adsorption constants of reacting species, three different isothermal spatiotemporal structures can arise, namely a spatially inhomogeneous stationary state, regular and aperiodic “breathing structures”.

Modulating N–H Bond Cleavage in Catalytic Ammonia Oxidation Reaction

The ammonia oxidation reaction (AOR) exhibits significant potential for environmental remediation and energy utilization. Nevertheless, the complex reaction mechanism of the AOR poses numerous challenges to its application. To overcome these challenges and realize an efficient AOR process, a thorough understanding of every elementary reaction step, especially the cleavage of N–H bonds, is crucial. This review delves into the influence of N–H bond cleavage on the rate and selectivity of AOR, and summarizes the latest advancements in promoting this crucial step. Furthermore, we discuss the challenges faced by N–H bond cleavage and provide insights into the design of efficient catalytic AOR systems.

Persistent ultraviolet luminescence and photocatalytic properties of SiO2-Zn2SiO4:Ga,Pb nanoparticles

Persistent phosphors possess unique afterglow optical properties. In this paper, a class of ultra-violet (UV) persistent luminescence nanoparticles were developed for catalytic photodegradation applications. UV persistent luminescence nanoparticles of SiO2-Zn2SiO4:Ga and SiO2-Zn2SiO4:Ga,Pb were successfully synthesized by using a mesoporous template method. The UV persistent luminescence intensity of SiO2-Zn2SiO4:Ga at 405 nm was enhanced up to ca. 3.5 times by co-doping with Pb2+ (396 nm), along with longer persistent luminescence duration. The photodegradation results indicate that it is useful to introduce UV persistent luminescence property into SiO2-Zn2SiO4:Ga,Pb to obtain enhanced catalytic activity of SiO2-Zn2SiO4 with a bigger catalytic oxidation reaction kinetic constant (up to ∼4 times). This kind of UV persistent catalysis strategy may become a potential feasible method for better catalytic photodegradation activity. The UV persistent photocatalyst has potential applications in the photooxidation of organic molecules in high chroma and/or turbidity aqueous systems.

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.

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.

Enhancing acidity of Ru/Ce/ZrO2 bifunctional catalysts for promoting N2 selectivity in selective catalytic oxidation of NH3

To solve the problem of low N2 selectivity of Ru/Ce/ZrO2 (R/C/Z) catalysts in NH3 selective catalytic oxidation (NH3-SCO) reaction, herein ZrO2 supports were treated with sulfuric acid and its effects on NH3-SCO performance were investigated systematically. The results showed that Ru/Ce/ZrO2-10S (R/C/Z-10S) catalyst, in which the mass ratio of sulfuric acid to ZrO2 was 10 %, exhibited N2 selectivity of 95.7 % at 350 °C, that was significantly higher than R/C/Z catalyst (57.8 %). NH3-TPD tests indicated that sulfate treatment of ZrO2 supports in R/C/Z catalysts led to more abundant acidic sites on catalyst surface, which was in favor of enhancing NH3 adsorption capacity remarkably. But when mass ratio of sulfuric acid to ZrO2 increased up to 20 %, an aggregation of metal oxides on the surface of R/C/Z-20S catalyst could be observed clearly, which might impose an adverse impact on NH3-SCO performance. In-situ DRIFTS results revealed that, compared to R/C/Z catalyst, there were much more Brönsted acid sites on the surface of R/C/Z-10S catalyst, and the corresponding NH3 species on acidic sites could be consumed quickly in intermediate reactions. More importantly, amide (-NH2) species rather than imide (-NH) and nitrosyl (-HNO) species, were the majority on the surface of R/C/Z-10S catalyst, implying that there might be a suppressing effect on further dehydrogenation of -NH2 species into -NH species owning to sulfate treatment of ZrO2 supports in R/C/Z catalysts. Therefore, internal selective catalytic reduction (i-SCR) mechanism rather than -NH mechanism played a vital role in NH3-SCO reaction over R/C/Z-10S catalyst.

Carbonaceous structures as electronic bridges to enhance charge migration and radical reactions in composite photocatalysts: An effective way to achieve efficient mineralization of pollutants

The intrinsic correlation between photo-induced extraction of hole and free radical reactions can facilitate the mineralization of contaminants via promoting the transfer of electrons from the semiconductor to the solution. TiO2/C/g-C3N4 composite photocatalysts are prepared using thermal polycondensation and sol-gel methods in this paper. The introduction of carbon at the interface between the two phases creates charge migration channels that facilitate electron transfer at the interface of semiconductor catalyst as well as collisions of dissolved oxygen to the catalytic sites, which are able to promote catalytic oxidation reactions. Considering Rh-B as target, the removal rate is 97.2±0.2 % within 90 min. The involvement of hydroxyl radicals and superoxide radicals is confirmed by carrying out radical quenching experiments and ESR characterization, suggesting that effective electron transfer synergistically promotes the production of hydroxyl radicals. Therefore, it emphasizes the importance of the indeterminate carbon bridged 2D/3D interface for constructing charge migration channels as well as promoting the efficiency of carrier separation in the process of photocatalytic efficient degradation of dyes.

Highly efficient Rh-doped MnO2 nanocatalysts for complete elimination of CO at room temperature.

Obliteration of carbon monoxide is significant due to its hazardous effect on human health and potential application in different fields. Catalytic CO oxidation at lower temperature is the most convenient method to diminish the toxicity of CO. The low-cost catalysts which are exhibiting higher activity at lower temperature with good stability are in demand. The nanosized Rh-doped MnO2 catalysts have been prepared by dextrose-assisted co-precipitation method. Catalytic CO oxidation reaction was carried out over these prepared nanocatalysts under environmentally suitable conditions. XRD confirms the phase formation of prepared catalysts. These samples exhibit rod-like morphology with thickness of rods of less than 10nm which is substantiated from electron microscopy images. XPS data reveals the oxidation state of Mn (+ 4) and Rh (+ 3). These catalysts are highly active for CO oxidation reaction at lower temperature, and one showed complete CO conversion at room temperature. The time-on-stream studies revealed that these catalysts are highly stable for CO oxidation for several hours. These catalysts are decidedly stable in moist condition and also showed higher activity in the presence of moisture, indicating participation of moisture in the oxidation reaction at above room temperatures.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2–) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

Synthesis of La1-xSrxCoO3-δ and its catalytic oxidation of NO and its reaction path

The oxidation rate of NO to NO2 is a critical parameter in the removal of NOx within selective catalytic reduction (SCR) systems. LaCoO3-δ is a kind of potential catalyst to enhance the oxidation of NO to NO2, it may offers an economic and stable alternative to noble metal catalysts, particularly at elevated temperatures. This study aimed to enhance the catalytic efficiency of LaCoO3-δ through strontium (Sr) doping. La1-xSrxCoO3-δ (with varying x values of 0.1, 0.2, 0.3, 0.4) was synthesized using a sol-gel method. La1-xSrxCoO3-δ exhibited superior NO oxidation catalytic activity compared to LaCoO3-δ, with the most notable enhancement observed at x = 0.3 (84 % conversion). This improvement can be attributed to the substitution of La3+ with Sr2+, which induces lattice distortion and charge imbalance, thereby creating more oxygen vacancies that enhance the catalytic oxidation capability of La1-xSrxCoO3-δ. However, it's important to note that an excessive amount of Sr can result in the formation of SrCO3 deposits on the surface of La1-xSrxCoO3-δ, thereby diminishing its catalytic oxidation performance. The catalytic oxidation reaction behavior adhered most closely to the O2-adsorbed E-R model, the surface defects in La1-xSrxCoO3-δ playing a pivotal role in the catalytic reaction.

Polygonal mesopores microflower catalysts for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene to 2-nitro-4-methylsulfonylbenzoic acid in a continuous-flow microreactor

The development of efficient systems for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) to 2-nitro-4-methylsulfonyl benzoic acid (NMSBA) with atmospheric air or molecular oxygen in alkaline medium presents a significant challenge for the chemical industry. Here, we report the synthesis of FeOOH/Fe3O4/MOF polygonal mesopores microflower templated from a MIL-88B(Fe) at room temperature, which exposes polygonal mesopores with atomistic edge steps and lattice defects. The obtained FeOOH/Fe3O4/MOF catalyst was adsorbed onto glass beads and then introduced into the microchannel reactor. In the alkaline environment, oxygen was used as oxidant to catalyze the oxidation of NMST to NMSBA, showing impressive performance. This sustainable system utilizes oxygen as a clean oxidant in an inexpensive and environmentally friendly NaOH/methanol mixture. The position and type of substituent critically affect the products. Additionally, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. Moreover, compared with the traditional batch reactor, the self-built microchannel reactor can accelerate the reaction rate, shorten the reaction time and enhance the selectivity of catalytic oxidation reactions. This approach contributes to environmental protection and holds potential for industrial applications.

Structural evolution in S-vacancy-rich Co@Co9S8 during selective benzyl alcohol electrooxidation reaction

Electrooxidation of organics using electrons as oxidants is a clean approach to produce commodity chemicals. However, designing an electrocatalyst with superior performance at low cell voltage remains a challenge. In this study, a series of VS-Co@Co9S8 electrocatalysts were fabricated by thermal reduction method using MOFs as templates. The catalytic oxidation performance and reaction mechanism of such specimens for benzyl alcohol were comprehensively analyzed by electrochemical measurement method and ex-situ structure characterization. The results show that Co@Co9S8-30 M has a unique three-dimensional (3D) micro cubic structure with abundant S vacancy (VS). These features accelerate the electrons and substrate transfer as well as provide plentiful active sites for benzyl alcohol electrooxidation reaction (BAOR). Consequently, the Co@Co9S8-30 M presented outstanding catalytic activity. The overpotential of 10 mA cm−2 (η10) was only 265.4 mV for BAOR. The conversion rate and benzoic acid selectivity were achieved to 72% and 90%, respectively. Particularly, the formation rate of benzoic acid was 7.247 mmol·gcat.−1·h−1. Moreover, the Co@Co9S8-30 M exhibited superior durability over 135 h. The coordination number of octahedral metal sites in Co9S8 did not match the number of Co 3 d orbital electrons, resulting in the weakening of bonding strength between Co and S elements. Thus, the Co@Co9S8 was reconstructed to Co3O4@CoOOH. Based on this assessment, the Co3O4@CoOOH was the active site of BAOR. This work provides theoretical guidance for the design of Co-based catalysts.