Mechanism Of Selective Oxidation Research Articles

Mechanism and Kinetics of Selective Aerobic Oxidation of n-Butane to Methyl Ethyl Ketone Catalyzed by Cu(HPTB)/NHPI

Mechanism and Kinetics of Selective Aerobic Oxidation of <i>n</i>-Butane to Methyl Ethyl Ketone Catalyzed by Cu(HPTB)/NHPI

Origins of Selective Oxidation in Carbon-Based Nonradical Oxidation Processes toward Organic Pollutants: Quantitative Structure-Activity Relationships (QSARs).

Metal-free carbon material-mediated nonradical oxidation processes (C-NOPs) have emerged as a research hotspot due to their excellent performance in selectively eliminating organic pollutants in aqueous environments. However, the selective oxidation mechanisms of C-NOPs remain obscure due to the diversity of organic pollutants and nonradical active species. Herein, quantitative structure-activity relationship (QSAR) models were employed to unveil the origins of C-NOP selectivity toward organic pollutants in different oxidant systems. QSAR analysis based on adsorption and oxidation descriptors revealed that C-NOP selectivity depends on the oxidation potentials of organic pollutants rather than on adsorption interactions. However, the dominance of electronic effects in selective oxidation decreases with increasing structural complexity of organic pollutants. Moreover, the oxidation threshold solely depends on the inherent electronic nature of organic pollutants and not on the reactivity of nonradical active species. Notably, the accuracy of substituent descriptors (Hammett constants) and theoretical descriptors (e.g., highest occupied molecular orbital energy, ionization potential, and single-electron oxidation potential) is significantly influenced by the complexity and molecular state of organic pollutants. Overall, the study findings reveal the origins of organic pollutant-oriented selective oxidation and provide insight into the application of descriptors in QSAR analysis.

The Mechanism and Pathway of Selective Partial Oxidation of n-Butane to Maleic Anhydride Studied on Titanium Phosphate Catalysts

The Mechanism and Pathway of Selective Partial Oxidation of <i>n</i>-Butane to Maleic Anhydride Studied on Titanium Phosphate Catalysts

Phase reconstruction of Co3O4 with enriched oxygen vacancies induced by cold plasma for boosting methanol-to-formate electro-oxidation

Developing high-performance Pt-free electrocatalysts for the electro-oxidation of methanol (MeOH) into high-value-added formate in alkaline media offers a sustainable avenue for synchronous biomass valorization and MeOH oxidation-assisted hydrogen production. Herein, electrodeposited Co(OH)2 on Ni foam (NF) was treated by an O2 cold plasma to obtain oxygen vacancies enriched Co3O4-x/NF-P. The resultant Co3O4-x/NF-P only requires a potential of 1.318 V vs. RHE to upgrade MeOH into formate at 10 mA·cm−2. Characterization and calculation results reveal that oxygen vacancy induced irreversible phase transformation of Co3O4-x/NF-P, facilitating the deprotonation of MeOH, and suppressing further oxidation of HCOO* for selective and efficient formate electrosynthesis. Impressively, a Co3O4-x/NF-P||Co3O4-x/NF-P pair was built to couple the MeOH electro-oxidation with H2 evolution, where it only supplies a cell voltage of 1.540 V at 10 mA·cm−2 and the anodic Faraday efficiency exceeds 95 %. This work clarifies in-depth insight the underlying mechanism of MeOH selective oxidation into formate.

Targeted NO Oxidation and Synchronous NO2 Inhibition via Oriented 1O2 Formation Based on Lewis Acid Site Adjustment.

An appealing strategy for ensuring environmental benefits of the photocatalytic NO oxidation reaction is to convert NO into NO3- instead of NO2, yet the selectivity of products remains challenging. Here, such a scenario could be realized by tailoring the exposure of Lewis acid sites on the surface of ZrO2, aiming to precisely regulate the ROS evolution process for the selective oxidation of NO into NO3-. As evidenced by highly combined experimental characterizations and density functional theory (DFT) simulations, Lewis acid sites serving as electron acceptors could induce itinerant electron redistribution, charge-carrier transfer, and further oxidation of •O2-, which promotes the oriented formation of 1O2. As a result, monoclinic ZrO2 with more Lewis acid sites exhibited an outstanding NO conversion efficiency (56.33%) and extremely low NO2 selectivity (5.04%). The ROS-based reaction process and promotion mechanism of photocatalytic performance have been revealed on the basis of ESR analysis, ROS-quenching experiments, and in situ ROS-quenching DRIFTS. This work could provide a critical view toward oriented ROS formation and advance a unique mechanism of selective NO oxidation into NO3-.

Electron-transfer based selective oxidation of organic pollutants via N-doped biochar activated peroxydisulfate: Important role of oxidation potential

For persulfate-based advanced oxidation process, the non-radical pathway is an important route due to the selective oxidation of pollutants and its strong tolerance to complex water bodies. However, the selective oxidation mechanism of organic pollutants needs further elaboration. Herein, we demonstrate a facile hydrothermal pretreatment and high-temperature carbonization route to synthesize the nitrogen-doped porous biochar (NHBC-1). Owing to the well-developed hierarchical porous structure, the created internal active defects, and tailored nitrogen dopants, the NHBC-1 catalyst exhibited excellent catalytic activity for peroxydisulfate (PDS) activation. The results show that pyridinic N facilitated the adsorption of PDS on NHBC-1 to form the highly active NHBC-PDS* complex. Meanwhile, graphitic N and the defective structures promoted the electron-transfer process, thus allowing the efficient catalytic performance of the NHBC/PDS system for phenol oxidation via an electron-transfer dominated pathway. In addition, the system exhibited versatile applicability for the remediation of various organic pollutants in different actual water matrices with wide pH adaptability and satisfactory mineralization efficiency. More importantly, the selective oxidation mechanism of organic contaminants was revealed. Specifically, only the pollutant with oxidation potential lower than that of the NHBC-PDS* complex (0.91 V) can be effectively eliminated. This study not only provides a facile route for the rational designing of a cost-affordable biochar catalyst for PDS activation, but also offers valuable insights into the understanding of selective oxidation of organic contaminants via an electron-transfer dominated pathway.

Highly Selective Oxidation of Toluene to Benzaldehyde in Alkaline Systems

For the selective oxidation of toluene to benzaldehyde, the biggest challenge is to prevent the further oxidation of benzaldehyde as toluene conversion increases. Using benzyl benzoate as the solvent and adding benzoate to adjust the alkalinity of the system, the formation of the benzoyl radical can be well inhibited, but the oxidation of toluene is weakened. The decomposition of benzyl benzoate to benzaldehyde can activate the reaction at the initial stage, and the negative influence of alkalinity is avoided to some extent. Therefore, by using atmospheric air as an oxidant, a high selectivity and yield of benzaldehyde can be obtained in a benzyl benzoate catalytic system with alkali as an additive. The mechanism of alkaline regulation and selective oxidation of toluene was investigated by in situ infrared (IR) spectroscopy experiments. The benzaldehyde capacity is defined to characterize the tolerance of benzaldehyde in the system. Catalysts and alkaline regulators can be easily reused with high-boiling solvents, making it a convenient process for product separation and catalyst–alkaline solvent recycling.

Fabrication of CuTNPc/MWCNTs composites by in-situ solvothermal method for efficient selective oxidation of styrene

The tetranitro-copper phthalocyanine/multi-walled carbon nanotubes (CuTNPc/MWCNTs) composites have been successfully fabricated by a straightforward in-situ solvothermal approach. The as-prepared CuTNPc/MWCNTs composites can be used as effective catalysts for the styrene catalytic oxidation to benzaldehyde. Effects of solvent type, oxidant type, catalyst dose, and reaction temperature on catalytic performance are investigated. It can be found that the CuTNPc/MWCNTs composites showed significant catalytic oxidation of styrene activity. Under the optimal conditions of 0.3 g styrene, 20 mg CuTNPc/MWCNTs, 3 mL TBHP as oxidant, and 5 mL THF at 90 ℃ for 6 h, the styrene conversion, and benzaldehyde selectivity could reach 99.74% and 79.53%, respectively. In addition, the possible reaction mechanism of styrene selective oxidation to benzaldehyde by CuTNPc/MWCNTs is also proposed.

Zinc Vacancy Promotes Photo-Reforming Lignin Model to H2 Evolution and Value-Added Chemicals Production.

Lignin, rich in β-O-4 bonds and aromatic structure, is a renewable and potential resource for value-added chemicals and promoting H2 evolution. However, direct photo-reforming lignin remains a huge challenge due to its recalcitrant structure. Herein, a collaborative strategy is proposed by dispersing Pt on zinc-vacancy-riched ZnIn2 S4 (Pt/VZn -ZIS) for revealing the effect of lignin structure during photo-reforming process with lignin models. And a series of theoretical calculations and experimental results show that lignin model substances with more nucleophilic group structures will have a stronger tendency to occur the photo-reforming reactions. In addition, benefiting of Pt-S electronic channel is formed by occupying Pt atom onto zinc vacancies in ZnIn2 S4 , which can effectively reduce the energy barrier of H2 evolution and accompany the selective oxidation of lignin model from Cα-OH to Cα = O under simulated sunlight. The natural lignin is used to further demonstrate this selective oxidation mechanism. The presented work demonstrates the photo-reforming lignin model mechanism and the influence of lignin-structure during the process of photo-reforming.

Electrochemical activation of periodate with graphite electrodes for water decontamination: Excellent applicability and selective oxidation mechanism

Advanced oxidation technologies based on periodate (PI, IO4−) have garnered significant attention in water decontamination. In this work, we found that electrochemical activation using graphite electrodes (E-GP) can significantly accelerate the degradation of micropollutants by PI. The E-GP/PI system achieved almost complete removal of bisphenol A (BPA) within 15 min, exhibited unprecedented pH tolerance ranging from pH 3.0 to 9.0, and showed more than 90% BPA depletion after 20 h of continuous operation. Additionally, the E-GP/PI system can realize the stoichiometric transformation of PI into iodate, dramatically decreasing the formation of iodinated disinfection by-products. Mechanistic studies confirmed that singlet oxygen (1O2) is the primary reactive oxygen species in the E-GP/PI system. A comprehensive evaluation of the oxidation kinetics of 1O2 with 15 phenolic compounds revealed a dual descriptor model based on quantitative structure−activity relationship (QSAR) analysis. The model corroborates that pollutants exhibiting strong electron-donating capabilities and high pKa values are more susceptible to attack by 1O2 through a proton transfer mechanism. The unique selectivity induced by 1O2 in the E-GP/PI system allows it to exhibit strong resistance to aqueous matrices. Thus, this study demonstrates a green system for the sustainable and effective elimination of pollutants, while providing mechanistic insights into the selective oxidation behaviour of 1O2.

Unveiling different antibiotic degradation mechanisms on dual reaction center catalysts with nitrogen vacancies via peroxymonosulfate activation

Metal-nitrogen-site catalysts are widely recognized as effective heterogeneous catalysts in peroxymonosulfate (PMS)-based advanced oxidation processes. However, the selective oxidation mechanism for organic pollutants is still contradictory. In this work, manganese-nitrogen active centers and tunable nitrogen vacancies were synchronously constructed on graphitic carbon nitride (LMCN) through l-cysteine-assisted thermal polymerization to reveal different antibiotic degradation mechanisms. Benefiting from the synergism of manganese-nitrogen bond and nitrogen vacancies, the LMCN catalyst exhibited excellent catalytic activity for the degradation of tetracycline (TC) and sulfamethoxazole (SMX) antibiotics with first-order kinetic rate constants of 0.136 min−1 and 0.047 min−1, which were higher than those of other catalysts. Electron transfer dominated TC degradation at low redox potentials, while electron transfer and high-valent manganese (Mn (V)) were responsible for SMX degradation at high redox potentials. Further experimental studies unveiled that the pivotal role of nitrogen vacancies is to promote electron transfer pathway and Mn(V) generation, while nitrogen-coordinated manganese as the primary catalytic active site determines Mn(V) generation. In addition, the antibiotic degradation pathways were proposed and the toxicity of byproducts was analyzed. This work provides an inspiring idea for the controlled generation of reactive oxygen species by targeted activation of PMS.

Novel internal oxidation behavior of new 17Cr2Ni2MoVNb steel

The oxidation behavior of 17Cr2Ni2MoVNb steel in air was studied at different temperatures using advanced characterization techniques. The variation in oxidation products with temperature was revealed, and the selective oxidation mechanism at the front of the inner oxide layer was determined. Factors affecting the morphology, composition, and structure of the oxide near the interface were determined. A novel internal oxidation model with a multilayer core/shell structure induced by defects and interfaces was proposed, which was mainly controlled by the diffusion pathway of oxygen, thermodynamic properties, and intragranular defects.

Methane Oxidation over the Zeolites-Based Catalysts

Zeolites have ordered pore structures, good spatial constraints, and superior hydrothermal stability. In addition, the active metal elements inside and outside the zeolite framework provide the porous material with adjustable acid–base property and good redox performance. Thus, zeolites-based catalysts are more and more widely used in chemical industries. Combining the advantages of zeolites and active metal components, the zeolites-based materials are used to catalyze the oxidation of methane to produce various products, such as carbon dioxide, methanol, formaldehyde, formic acid, acetic acid, and etc. This multifunction, high selectivity, and good activity are the key factors that enable the zeolites-based catalysts to be used for methane activation and conversion. In this review article, we briefly introduce and discuss the effect of zeolite materials on the activation of C–H bonds in methane and the reaction mechanisms of complete methane oxidation and selective methane oxidation. Pd/zeolite is used for the complete oxidation of methane to carbon dioxide and water, and Fe- and Cu-zeolite catalysts are used for the partial oxidation of methane to methanol, formaldehyde, formic acid, and etc. The prospects and challenges of zeolite-based catalysts in the future research work and practical applications are also envisioned. We hope that the outcome of this review can stimulate more researchers to develop more effective zeolite-based catalysts for the complete or selective oxidation of methane.

Catalytic activity and mechanism of selective catalytic oxidation of ammonia by Ag-CeO2 under different preparation conditions.

Given the problem of the high-temperature window of CeO2 catalyst activity, this study evaluated the catalytic properties of Ag/CeO2 prepared by changing the preparation methods and loadings. Our experiments showed that Ag/CeO2-IM catalysts prepared by the equal volume impregnation method could have better activity at lower temperatures. The Ag/CeO2-IM catalyst achieves 90% NH3 conversion at 200 °C, and the main reason is that the Ag/CeO2-IM catalyst has more vital redox properties, and the NH3 catalytic oxidation temperature is lower. However, its high-temperature N2 selectivity still needs to be improved and may be related to the less acidic sites on the catalyst surface. On both catalyst surfaces, the i-SCR mechanism governs the NH3-SCO reaction.

COMPARATIVE CATALYTIC STUDY OF PURE COBALT OXIDE SPINEL AND NON-NOBLE METAL DOPED COBALT OXIDE SPINEL FOR SELECTIVE OXIDATION OF ALCOHOL TO ALDEHYDE: A REVIEW

The selective oxidation of alcohol by heterogeneous catalysts, such as noble and non-noble metal oxide spinels and doped metal oxide spinels, is one of the challenging and interesting routes in catalysis. In this review, the selective oxidation mechanism of non-noble cobalt oxide spinel and various metal-doped cobalt oxide spinel-based catalyst systems are examined. Selective oxidation of alcohol to aldehyde by using cobalt oxide spinel (Co&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;) and various metal-doped cobalt oxide spinels (Fe, Mn, Ni, Al, Cu, Sr) has been reviewed carefully. The selective oxidation by pure cobalt oxide spinel showed higher activity. However, a large number of studies have also been devoted to selective oxidation by various metal-doped cobalt oxide spinels. The metal-doped Co&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; showed higher selective oxidation activity compared to the pure spinel Co&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;. The mechanistic aspects and the role of cobalt and doping metal in the selective oxidation of alcohol have been studied thoroughly.

Selective oxidation of ammonia to dinitrogen gas by facile Co2+/PMS/chloridion process through reactive chlorine radicals

The selective oxidation of ammonia to dinitrogen gas in some special wastewater is of paramount significance, but still a challenge. In this study, chlorine radical (Cl•)-mediated oxidation process was developed to realize the selective oxidation of NH4+-N to N2, in which Cl• was generated in Co2+/peroxymonosulfate (PMS)/chloridion (Cl−) system. The effect of various operational parameters on the efficiency and selectivity of ammonia oxidation to N2 was investigated, such as PMS concentration, Co2+ concentration, Cl− concentration and pH value. The experiment results showed that Cl•-mediated NH4+-N oxidation reaction exhibited high NH4+-N removal efficiency and considerable selectivity to N2 in the range of pH from 2.0 to 6.5. The removal efficiency of NH4+-N was 90.39%, and the selectivity of NH4+-N to N2 achieved up to 97.16%. The possible mechanism for high efficient and selective oxidation of NH4+-N to N2 was tentatively proposed. The process developed in this study could provide a novel technology for the treatment and selective oxidation of ammonium in some special types of ammonium-containing wastewater.

A DFT Study on the Mechanism of Active Species in Selective Photocatalytic Oxidation of Toluene into Benzaldehyde on (WO3)3 Clusters

AbstractIt is of great significance to transform toluene into value‐added aldehydes under mild conditions, but the oxidation mechanism is still unclear, which seriously hinders the development of this direction. To reveal the nature of photocatalytic reaction, we studied the reaction mechanism of photocatalytic selective oxidation of toluene into benzaldehyde (BAD) on (WO3)3 clusters by density functional theory calculation, and analyzed the effect of active species on the reaction, including electrons, holes, dissolved oxygen (O2), superoxide radical anions (⋅O2−), hydroxyl radicals (⋅OH) and hydroperoxyl radicals (⋅OOH). The results show that ⋅OH and ⋅OOH play a major role in the reaction, from which we summarized two main pathways for BAD production. The direct oxidation of toluene to BAD is dominated by ⋅OOH and has higher selectivity. The oxidation process dominated by ⋅OH first converts toluene to benzyl alcohol (BA), and then BA continues to be oxidized to BAD. This path is more thermally advantageous because the dehydration energy barrier of C6H5CHOHOH (IM5) (22.3 kcal mol−1) is lower than that of C6H5CH2OOH (IM2) (42.9 kcal mol−1). However, the selectivity of this path is low because ⋅OH and holes can easily oxidize BAD to benzoic acid. Notably, water molecules reduced the energy barrier for dehydration of IM2 and IM5 by 12.4 kcal mol−1 and 13.0 kcal mol−1, respectively. The results elucidate the mechanism of free radicals involved in the photocatalytic reaction at molecular level.

Simultaneous Photoelectrocatalytic Oxidation and Nitrite‐Ammonia Conversion with Artificial Photoelectrochemistry Cells

AbstractArtificial photoelectrochemistry system harvests solar energy for solar fuel conversion by use of semiconductor anode and cathode. However, the low overall performance of this integrated system is limited by the compatibility and durability. Herein, a compact heterostructure photoanode exhibits &gt;98% selective photoelectrocatalytic oxidation conversion and &gt;99% Faradaic efficiency of benzyl alcohol oxidation at 0.67 V versus reversible hydrogen electrode in comparison of single‐phase photoanodes. Density functional theory calculations reveal the heterointerface is responsible for the appreciable electronic interaction and the accelerated charge transport, exploring the radical relay pathway as the selective oxidation mechanism. Especially, the integrated photoelectrochemistry cell is developed by heterostructure photoanode and protective photocathode, simultaneously enabling the efficient photoelectrocatalytic oxidation conversion and nitrite reduction reaction to ammonia synthesis under ambient conditions with a maximum Faradaic efficiency &gt;98%. This work sheds light on rational design and the construction of artificial photoelectrochemistry cells towards solar energy conversion.

Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel: Microstructure evolution and a synergistic selective oxidation mechanism

In this study, Fe-24Mn-2Al-0.45C twinning-induced plasticity (TWIP) steel was investigated after active screen plasma nitriding (ASPN) at 350–480 °C. Up to 450 °C, the ASPN-treated TWIP steel showed a double-layered structure, with a topmost Fe4N-type γ’ layer and an underlying interstitial solid solution. The underlying nitrogen interstitial solid solution obtained on ASPN-treated TWIP steel can be identified as γN(i), being expanded austenite with small lattice expansions at low nitrogen (and carbon) absorption levels. However, the 480 °C ASPN-treated TWIP steel surface is composed of an unexpected MnO-containing ferritic topmost layer and a thick underlying γN(i) layer, which corresponds to a hardness-depth profile different to those obtained at 350–480 °C. Hence, we propose and elucidate a selective oxidation mechanism (that occurred alongside nitrogen inward diffusion) on TWIP steel during ASPN treatment, which can be attributed to (a) an elevated treatment temperature that allowed Mn migration, (b) a processing atmosphere with low oxygen partial pressure, and (c) a high-Mn substrate chemical composition with low Al/Mn (or Si/Mn) ratio.

High thermal stability and oxidation behavior of FeCrNiAl-based medium-entropy alloys prepared by powder metallurgy

The thermal stability and oxidation behavior of powder metallurgical FexCrNiAl medium-entropy alloys at 800 °C~1000 °C were investigated in the air. The as-sintered alloys show fine microstructures with the major phases of BCC, disordered BCC(B2), dispersed oxides together with a small volume fraction of carbides. After long-time annealing, the alloys show excellent thermal stability maintaining the phase constitution obtained from the as-sintered alloys. The oxides and carbides introduced by mechanical alloying inhibit grain growth, which plays a significant role in thermal stability. After isothermal oxidation, the oxide scale follows the sequence of outer-layer Al2O3, middle-layer Cr2O3, and inner-layer spinels respectively. The results indicate that decreasing Fe enhances the oxidation resistance of FeCrNiAl-based alloys by slowing down the oxidation kinetics and reducing the oxide stress. The high internal stress leads to the spallation and wrinkling of the oxide scale at 1000 °C. The reasons for spallation are systematically discussed from the aspect of composition, sample geometry, and oxidation conditions. The selective oxidation mechanism of FeCrNiAl-based high-entropy alloys was proposed.