Heterogeneous Oxidation Reactions Research Articles

Cooling radiative forcing effect enhancement of atmospheric amines and mineral particles caused by heterogeneous uptake and oxidation

Abstract. The warming radiative forcing effect (RFE) derived from atmospheric amines attracts a lot of attention because of their contribution to brown carbon. Herein, the enhanced influence of amines (methyl-, dimethyl-, and trimethylamine) on cooling RFE of mineral particles is first confirmed at visible wavelengths. Present results state heterogeneous uptake and oxidation reactions of atmospheric amines are feasible on mineral particles under clean and polluted conditions, which are proven by related thermodynamics and kinetics data obtained using combined classical molecular dynamics and density function theory methods. Based on mineral particles, simple forcing efficiency (SFE) results explain that amine uptake induces at least 11.8 %–29.5 % enhancement on cooling RFE of amine–mineral particles at visible wavelengths. After amine heterogeneous oxidation, oxidized amine–mineral particle cooling RFEs are furthermore enhanced due to increased oxygen contents. Moreover, oxidized amine–mineral particles under clean conditions show 27.1 %–47.1 % SFE increments at 400–600 nm, which is at least 11.3 % higher than that of itself under polluted conditions, due to high-oxygen-content product formation through amine autoxidation. Our results suggest cooling RFE derived from atmospheric amines can be equally important to their warming RFE on the atmosphere. It is necessary to update the heterogeneous oxidation mechanism and kinetics data of amines in atmospheric models in order to accurately evaluate the whole RFE caused by amines on the atmosphere.

Evaluation of low-temperature oxidation analysis and the development effect of high-pressure air injection in low-permeability reservoirs

In order to solve the problems of conventional water injection development difficulties and low recovery factor in low-permeability reservoirs, the method of high-pressure air drive is adopted to achieve the purpose of reservoir energy enhancement and efficiency improvement. This paper conducted an experimental study on the mechanism of low-temperature oxidation (LTO) for crude oil in the process of high-pressure air flooding, elaborated the relationship between the LTO properties of crude oil and the temperature, pressure, and water saturation of the reservoir, and analyzed the differences in LTO oxygen consumption and oil components under different reaction conditions. In addition, combined with the air flooding physical simulation experiment, the dynamic evolution law of recovery rate in the air flooding process was revealed. Findings from this inquiry indicate that an escalation in the oxidation temperature significantly amplifies the oxygen incorporation reaction within the crude oil matrix. This augmentation in oxidative conditions leads to an uptick in oxygen consumption, which subsequently precipitates a reduction in the lighter fractions of the oxidized oil while enriching its heavier components. Elevated pressures were found to enhance the propensity for the amalgamation of unstable hydrocarbons with oxygen, fostering comprehensive and heterogeneous oxidation reactions. Notably, an excessive presence of water was observed to detrimentally affect the thermal efficacy of crude oil oxidation processes. In the context of low-permeability reservoirs, air injection techniques have emerged as superior in effectuating oil displacement, although an increase in injection pressures has been associated with the phenomenon of gas channeling. Interestingly, adopting a sequential strategy of initiating water flooding before air flooding facilitated the conveyance of high-pressure air via established flushing channels, although it appeared to attenuate the intensity of crude oil oxidation, culminating in an oil recovery efficiency peaking at 51%.

Development of a γ-Al2O3-Based Heterogeneous Fenton-like Catalyst and Its Application in the Advanced Treatment of Maotai-Flavored Baijiu Wastewater

Heterogeneous Fenton technology was employed for the advanced treatment of Maotai-flavored Baijiu wastewater. Novel catalysts were prepared by loading different active ingredients (Mn, Fe, and Cu) on γ-Al2O3 using an impregnation method. The effects of active ingredient, reaction time, initial pH, H2O2 dosage, catalyst dosage, and other factors on the reaction were examined. The properties of the new catalysts were analyzed using BET analysis, XPS, and SEM. Moreover, the mechanisms of Fenton-like oxidation and its reaction kinetics were explored through experiments and analyses including GC–MS and intermediate active species scavenging by tertiary butyl alcohol (TBA) and/or para-benzoquinone. The results revealed that the most effective removal of organic matter was achieved with a Mn-Fe/Al (2:1 wt%) catalyst dosage of 30 g/100 g water, pH of 5.0, H2O2 dosage of 0.3 g/L, and reaction time of 60 min; the effluent COD value was 12 ± 1 mg/L, and the degradation rate was 65.7 ± 3%, approximately 14% higher than that of the conventional Fenton catalyst under similar conditions; moreover, the catalytic efficacy remained high after seven cycles. Kinetic analysis indicated that the heterogeneous Fenton oxidation reaction followed a third-order kinetics model, with R2 = 0.9923 and K = 0.0006 min−1.

Quantifying SO2 oxidation pathways to atmospheric sulfate using stable sulfur and oxygen isotopes: laboratory simulation and field observation

Abstract. The formation of secondary sulfate in the atmosphere remains controversial, and it is an urgent need to seek a new method to quantify different sulfate formation pathways. Thus, SO2 and PM2.5 samples were collected from 4 to 22 December 2019 in the Nanjing region. Sulfur and oxygen isotopic compositions were synchronously measured to study the contribution of SO2 homogeneous and heterogeneous oxidation to sulfate. Meanwhile, the correlation of δ18O values between H2O and sulfate from SO2 oxidation by H2O2 and Fe3+ / O2 was simulatively investigated in the laboratory. Based on isotope mass equilibrium equations, the ratios of different SO2 oxidation pathways were quantified. The results showed that secondary sulfate constituted higher than 80 % of total sulfate in PM2.5 during the sampling period. Laboratory simulation experiments indicated that the δ18O value of sulfate was linearly dependent on the δ18O value of water, and the slopes of linear curves for SO2 oxidation by H2O2 and Fe3+ / O2 were 0.43 and 0.65, respectively. The secondary sulfate in PM2.5 was mainly ascribed to SO2 homogeneous oxidation by OH radicals and heterogeneous oxidation by H2O2 and Fe3+ / O2. SO2 heterogeneous oxidation was generally dominant during sulfate formation, and SO2 oxidation by H2O2 predominated in SO2 heterogeneous oxidation reactions, with an average ratio around 54.6 %. This study provided an insight into precisely evaluating sulfate formation by combining stable sulfur and oxygen isotopes.

Insight into Secondary Inorganic Aerosol (SIA) production enhanced by domestic ozone using a machine learning technique

Taiwan has prioritized management and air pollution control of ozone in the past decade. Atmospheric ozone reacts with gaseous precursors to produce secondary inorganic aerosols (SIAs), which worsen air quality to a great extent. The present study applied a bivariate polar plot, K-means clustering, and a nonlinear autoregressive network with exogenous input neural network (NARX-NN) to identify the sources of O3 and the formation mechanism of SIAs in an urban area, aiming to facilitate the development of exposure risk assessment methods and an O3 pollution early warning system for human health protection. Results show that the present NARX-NN model could be used to capture 72 h ahead of water-soluble inorganic salts (WIS) and O3 concentrations accurately with R2 of 0.71 for NO3-, 0.72 for SO42-, 0.80 for NH4+, and 0.79 for O3 concentrations. Based on the statistical and K-means clustering analysis, the domestic high O3 hours in a year (O3 concentrations>60 ppb) account for up to 76% and 99% of the total high O3 hours in northern and southern Taiwan, respectively. Under volatile organic compounds (VOCs)-limited regime, an increase in O3 concentrations by 57.4% was found to enhance heterogeneous oxidation reaction to produce SIAs by 48.0% of NO3- and 56.6% of SO42- under prevailing northeast monsoon during winter and spring seasons. It is evident that strict control measures are still necessary for local ozone sources to maintain air quality. The source tracing framework developed in the present study is applicable for policymakers to develop early warning systems and maintain air quality during the decision-making process.

Characterization and sources of water-soluble inorganic ions during sulfate-driven and nitrate-driven haze on the largest loess accumulation plateau

With the rapid reduction of anthropogenic SO2 emissions, the critical driver of haze in China has shifted from being dominated by sulfate to alternating sulfate and nitrate. Haze induced by different driver species may differ in the chemical forms of water-soluble inorganic ions (WSIIs). The unique topography and high-emission industrial agglomeration of the Loess Plateau determine its severe local PM2.5 pollution and influence global weather patterns through the outward export of pollutants. PM2.5 samples were conducted in Pingyao, on the eastern Loess Plateau of China, in autumn and winter. The average mass of PM2.5 was 88.82 ± 57.37 μg/m3; sulfate, nitrate, and ammonium were the dominant component. The chemical form of the ion was dominated by (NH4)2SO4, NH4NO3, NaNO3 and KNO3 during the nitrate-driven (ND) haze, while (NH4)2SO4, NH4HSO4, NH4NO3, NaNO3 and KNO3 were predominant species during the sulfate-driven (SD) haze. Heterogeneous oxidation reactions dominated the mechanism of sulfate formation. Primary sulfate emissions or other generation pathways contributed to sulfate formation during the SD haze. The gas-phase homogeneous reaction of NO2 and NH3 dominates the nitrate generation during the ND haze. The heterogeneous reactions also played an essential role during the SD haze. Nitrate aerosol (42.30%) and coal and biomass combustion (23.23%) were the dominant sources of WSIIs during the ND haze. In comparison, nitrate aerosol (31.80%) and sulfate aerosol (25.08%) were considered the primary control direction during the SD haze. The chemical characteristics and sources of aerosols under various types of haze differ significantly, and knowledge gained from this investigation provides insight into the causes of heavy haze.

Electrochemical enhanced heterogeneous activation of peroxymonosulfate by CoFe2O4 nanoparticles to degrade moxifloxacin

The catalytic mechanism of CoFe2O4 nanoparticles (NPs) was investigated in the system of electrochemical enhanced heterogeneous activation of peroxymonosulfate (EC/CoFe2O4/PMS) with moxifloxacin (MOX) as target contaminant. The removal efficiencies of MOX in PMS, CoFe2O4, EC, CoFe2O4/PMS, and EC/CoFe2O4/PMS system were 18.3%, 36.1%, 43.7%, 96.9%, and 98.3%, respectively. Although there was no synergy effect between EC and heterogeneous catalytic oxidation reaction (HCOR) on MOX removal, the value of apparent rate constant (karc) was much higher in EC/CoFe2O4/PMS system (0.24 min−1) compared with CoFe2O4/PMS system (0.13 min−1). Therefore, EC not only kept the structure of CoFe2O4 NPs stable, but also significantly accelerated the reaction rate of HCOR. Meanwhile, according to electrochemical impedance spectra of catalysts synthesized based on ion-substitution strategy and the EC-HCOR experimental results, the decisive role of Co in PMS activation and the electron transfer between Co and Fe were confirmed. The TOC removal efficiency was reached 74.4% as the ratio of PMS to CoFe2O4 NPs being 0.8 mM to 50 mg/L (30 min), and further improved to 87.6% with batch addition (0.25 mM per 30 min) of PMS (120 min, CoFe2O4 = 100 mg/L). The research results could improve the understanding of catalytic mechanism of spinel oxide in electrochemical system.

Inter‐Metal Interaction of Dual‐Atom Catalysts in Heterogeneous Catalysis

AbstractDual‐atom catalysts (DACs) have been a new frontier in heterogeneous catalysis due to their unique intrinsic properties. The synergy between dual atoms provides flexible active sites, promising to enhance performance and even catalyze more complex reactions. However, precisely regulating active site structure and uncovering dual‐atom metal interaction remain grand challenges. In this review, we clarify the significance of the inter‐metal interaction of DACs based on the understanding of active center structures. Three diatomic configurations are elaborated, including isolated dual single‐atom, N/O‐bridged dual‐atom, and direct dual‐metal bonding interaction. Subsequently, the up‐to‐date progress in heterogeneous oxidation reactions, hydrogenation/dehydrogenation reactions, electrocatalytic reactions, and photocatalytic reactions are summarized. The structure‐activity relationship between DACs and catalytic performance is then discussed at an atomic level. Finally, the challenges and future directions to engineer the structure of DACs are discussed. This review will offer new prospects for the rational design of efficient DACs toward heterogeneous catalysis.

Inter-Metal Interaction of Dual-Atom Catalysts in Heterogeneous Catalysis.

Dual-atom catalysts (DACs) have been a new frontier in heterogeneous catalysis due to their unique intrinsic properties. The synergy between dual atoms provides flexible active sites, promising to enhance performance and even catalyze more complex reactions. However, precisely regulating active site structure and uncovering dual-atom metal interaction remain grand challenges. In this review, we clarify the significance of the inter-metal interaction of DACs based on the understanding of active center structures. Three diatomic configurations are elaborated, including isolated dual single-atom, N/O-bridged dual-atom, and direct dual-metal bonding interaction. Subsequently, the up-to-date progress in heterogeneous oxidation reactions, hydrogenation/dehydrogenation reactions, electrocatalytic reactions, and photocatalytic reactions are summarized. The structure-activity relationship between DACs and catalytic performance is then discussed at an atomic level. Finally, the challenges and future directions to engineer the structure of DACs are discussed. This review will offer new prospects for the rational design of efficient DACs toward heterogeneous catalysis.

ABOUT THE POSSIBILITY OF USING THERMOCHEMICAL GAS ANALYZERS IN A MULTICOMPONENT MIXTURE

Kinetic parameters finding’s method of heterogeneous catalytic oxidation reactions of combustible gas’s small impurities in air on a thin platinum wire was described. It consists in obtaining from the wire’s current-voltage characteristic the dependence of the critical current values on its mass fraction in air. They corresponding to the catalytic ignition and extintion of the gas impurity. A method of determining the content of two combustible gases in the air, what based on processing the platinum wire’s current-voltage characteristic, was proposed. Depending on the level of the total gases concentration in the air, the determining experimental characteristics are not only the wire (catalyst) overheating relative to the inert wire under the conditions of catalytic ignition, but also the wire overheating during catalytic extinguishing or under conditions of self-sustaining catalytic combustion (without electric current heating).

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnOx), an adsorption-enhanced catalyst (MnOx-PP) was constructed for catalytic organic dyes oxidative-degradation. MnOx-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnOx-PP obtains lower ionization potential and O2 adsorption energy to promote the continuous generation of active substance (O2*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.

Significantly boosted activity for styrene oxidation through simultaneous regulation of porosity and copper sites in microporous metal–organic framework Cu-BTC

Herein, a series of novel HP-DEMOFs were prepared and employed as catalysts for the heterogeneous styrene oxidation reaction. They exhibited much higher conversion than that of the microporous Cu-BTC structure under the same reaction conditions.

Defective Metal‐Organic Frameworks with Tunable Porosity and Metal Active Sites for Significantly Improved Performance in Styrene Oxidation

Metal active sites and sufficient porosity in metal-organic frameworks (MOFs) are crucial parameters determining the performances of catalysis, guest molecule adsorption, etc. Herein, through in situ introduction of Ru sites with different levels to Cu-BTC structure together with post-synthetic activation at 180 °C, a series of hierarchically porous CuRu-BTC (HP-CuRu-BTC) MOFs were obtained. Besides, selective thermal decomposition (STD) treatment was carried out at 240 °C to further tune the hierarchical pores and metal sites, yielding rare case of metal nanoparticles (NPs)@HP-CuRu-BTC composites. After full characterization by XRD, N2 physisorption, SEM, ICP and XPS, these HP-CuRu-BTC and NPs@HP-CuRu-BTC samples possess high surface area (682-1199 m2 g-1 ), hierarchical pores and highly distributed metal sites with reduced oxidation states (Cu+ and Ru2+ ), indicating regulation of both metal sites and hierarchical pores. The HP-CuRu-BTC and NPs@HP-CuRu-BTC were further employed as catalysts for the heterogeneous styrene oxidation reaction under mild condition. Compared to microporous Cu-BTC with unary metal component, HP-CuRu-BTC-3 and NPs@HP-CuRu-BTC-3 exhibited more than 2 times higher styrene conversion after 7 hours reaction under same condition.

Classic deep oxidation CuMnOx catalysts catalyzed selective oxidation of benzyl alcohol

This work presents an extension of classic deep oxidation CuMnOx catalysts to a selective oxidation of alcohol with high efficiency and in an environmental-friendly reaction system. A series of CuMnOx catalysts characterized by CuO-Cu1.4Mn1.6O4 and Mn2O3-Cu1.4Mn1.6O4 oxide pairs were prepared via a novel half carbonized citrus grandis peel assisted hard template method. A shift of the oxide pairs from CuO-Cu1.4Mn1.6O4 to Mn2O3-Cu1.4Mn1.6O4 has been achieved by tuning Cu/Mn molar ratio, and then leads to a one-pass benzaldehyde yield more than 50% with 100% benzaldehyde selectivity in the selective oxidation of benzyl alcohol using H2O2 as oxidant. Higher relative amount of Cu1.4Mn1.6O4 in either Mn2O3-Cu1.4Mn1.6O4 or CuO-Cu1.4Mn1.6O4 oxide pair is found to be essential for achieving high catalytic activity. The interaction between the Cu1.4Mn1.6O4 constituent and Mn2O3 constituent of Mn2O3-Cu1.4Mn1.6O4 oxide pair is found to able to enhance the formation of Cu+ species, which can reacts with H2O2 to produce •OH and then touch off a Fenton-like catalytic oxidation process of benzyl alcohol, in the current CuMnOx-H2O2 system, to produce benzaldehyde with high selectivity. This work presents a new perspective in the development of highly effective and low cost CuMnOx catalysts for heterogeneous catalytic oxidation reactions.

Influence of Meteorological Factors and Chemical Processes on the Explosive Growth of PM2.5 in Shanghai, China

In order to explore the mechanism of haze formation, the meteorological effect and chemical reaction process of the explosive growth (EG) of PM2.5 were studied. In this study, the level of PM2.5, water-soluble inorganic ions, carbonaceous aerosols, gaseous precursors, and meteorological factors were analyzed in Shanghai in 2018. The EG event is defined by a net increase of PM2.5 mass concentration greater than or equal to 100 μg m−3 within 3, 6, or 9 h. The results showed that the annual average PM2.5 concentration in Shanghai in 2018 was 43.2 μg m−3, and secondary inorganic aerosols and organic matter (OM) accounted for 55.8% and 20.1% of PM2.5, respectively. The increase and decrease in the contributions of sulfate, nitrate, ammonium (SNA), and elemental carbon (EC) to PM2.5 from clean days to EG, respectively, indicated a strong, secondary transformation during EG. Three EG episodes (Ep) were studied in detail, and the PM2.5 concentration in Ep3 was highest (135.7 μg m−3), followed by Ep2 (129.6 μg m−3), and Ep1 (82.3 μg m−3). The EG was driven by stagnant conditions and chemical reactions (heterogeneous and gas-phase oxidation reactions). This study improves our understanding of the mechanism of haze pollution and provides a scientific basis for air pollution control in Shanghai.

Modified Polyethersulfone Ultrafiltration Membrane for Enhanced Antifouling Capacity and Dye Catalytic Degradation Efficiency

Catalytic membranes, as a combination of heterogeneous advanced oxidation and membrane technology reaction systems, have important application prospects in the treatment of dyes and other organics. In practical applications, it is still challenging to construct catalytic membranes with excellent removal efficiency and fouling mitigation. Herein, molybdenum disulfide-iron oxyhydroxide (MoS2-FeOOH) was fabricated using iron oxide and MoS2 nanoflakes, which were synthesized by the hydrothermal method. Furthermore, by changing the concentration of MoS2-FeOOH, the MoS2-FeOOH/polyethersulfone (PES) composite ultrafiltration membrane was obtained with improved hydrophilicity, permeability, and antifouling capacity. The pure water flux of the composite membrane reached 385.3 L/(m2·h), which was 1.7 times that of the blank PES membrane. Compared with the blank membrane, with the increase of MoS2-FeOOH content, the MoS2-FeOOH/PES composite membranes had better adsorption capacity and catalytic performance, and the membrane with 3.0% MoS2-FeOOH content (M4) could be achieved at a 60.2% methylene blue (MB) degradation rate. In addition, the membrane flux recovery ratio (FRR) of the composite membrane also increased from 25.6% of blank PES membrane (M0) to more than 70% after two cycles of bovine serum albumin (BSA) filtration and hydraulic cleaning. The membrane with 2.25% MoS2-FeOOH content (M3) had the best antifouling performance, with the largest FRR and the smallest irreversible ratio (Rir). Catalytic self-cleaning of the composite membrane M3 recovered 95% of the initial flux with 0.1 mol/L H2O2 cleaning. The MoS2-FeOOH/PES composite membranes with the functions of excellent rejection and antifouling capacity have a good prospect in the treatment of printing and dyeing wastewater composed of soluble dyes.

Molecular Structure Analysis and Mercury Adsorption Mechanism of Iron-Based Modified Biochar

The elemental composition, molecular skeleton vibration mode, and carbon-chain structure of iron-based modified biochar demercuration materials were studied on a microscopic scale using a variety of characterization methods. A three-dimensional molecular structure monomer model of iron-based modified biochar with defective carbon rings doped with high-valence metals was constructed. The reaction path of Hg0 adsorption on the surface of iron-based modified biochar was studied. The activation energy barrier and the rate-determining step of Hg0 adsorption on the surface of iron-based modified biochar were determined. Then, two reaction mechanisms and the corresponding bonding mechanism of Hg0 adsorption on modified biochar were proposed. In addition, the feasibility of regenerating biochar with different load ratios was verified and the regeneration reaction mechanism of inactivated biochar at different adsorption sites was revealed. The results show that the molecular structure of iron-based modified biochar is dominated by polycyclic aromatic carbon, and its molecular formula is C45H24O12NFe. Adsorption sites on iron-based modified biochar surface are not unique. A heterogeneous oxidation reaction occurs between Hg0, a Lewis base, and modified biochar, a Lewis acid. Hg-O-Fe-Ox–1 and the complex Hg-OM are the main products of Hg0 oxidation. Oxygen vacancies with electrons are the chemical adsorption sites, and Fe3+, lattice oxygen, and chemisorbed oxygen are the main oxidation sites on the modified biochar. The coupling of these four constituents enables the adsorption and oxidation of Hg0. Inactivated biochar can be regenerated by supplementing the lost lattice oxygen or chemisorbed oxygen with more oxygen. The maximum mercury adsorption efficiency decreased to 90% of the primary mercury adsorption efficiency. This study quantitatively revealed the mercury adsorption mechanism of iron-based modified biochar and the regeneration mechanism of inactivated biochar, laying a foundation for further improvements in the mercury adsorption efficiency of metal-modified biochar.

Confined heterogeneous catalysis by boron nitride-Co3O4 nanosheet cluster for peroxymonosulfate oxidation toward ranitidine removal

Peroxymonosulfate (PMS) induced advanced oxidation processes hold great promise for heterogeneous oxidation reactions. In this study, boron nitride (BN)-Co3O4 nanosheet cluster (NC) was fabricated to facilitate PMS activation with a nanoconfined heterogeneous catalysis effect for the rapid removal of ranitidine (RAN) under mild conditions. The obtained BN-Co3O4 NC cluster exhibited efficient catalysis performance with a 99.5% removal efficiency for ranitidine in 5 min, and meanwhile this novel catalyst could be applied under a wide pH range (pH: 3–9) with still high degradation efficiencies. The porous structure of BN-Co3O4 NC provided a large number of channels for RAN and PMS molecules to enter the catalyst’s inner confinement space, resulting in a remarkable enhancement of catalytic performance. The kinetic rate constant for RAN degradation by the BN-Co3O4 NC/PMS system with 3–33 fold less catalyst dosage is much larger (1.58–213 fold) compared with the state-of-the-art. PMS activation by BN-Co3O4 NC was mainly due to the pathway of reduction via active radicals. Density functional theory calculations specified that the concomitant active radicals such as ∙OH and SO4∙− were mainly derived from PMS activation via O-O bond cleavage. This work provides a new perspective for regulating the structure of Co3O4 and elucidating the mechanism of PMS-induced heterogeneous catalytic oxidation.

On the CuO-Mn2O3 oxide-pair in CuMnOx multi-oxide complexes: Structural and catalytic studies

The current work provide a new understanding on the active site of CuMnOx catalysts and thus offer a new perspective in the development of highly effective and low cost CuMnOx catalysts for heterogeneous catalytic oxidation reactions. A series of dual-component copper-manganese multi-oxide catalysts (CuMnOx) have been successfully synthesized using a surfactant assisted hydrolysis-hydrothermal method and studied by XRD, N2 adsorption–desorption test, ICP-AES, SEM, Aberration-corrected HADDF-STEM, HRTEM, FT-IR, Raman, XPS, H2-TPR. These CuMnOx catalysts were found to be composed with uniform CuO-Mn2O3 oxide pair structure, in which highly isolated/dispersed CuO species are anchored in the framework of Mn2O3. It was found that the speciation in these CuMnOx catalysts presents a shift from highly isolated or even single Cu2+ oxide species (Cu2+Ox) to CuO nanoclusters and CuO microcrystalline with increasing Cu content. In CO oxidation reaction, which was employed to probe the structure of the CuO-Mn2O3 oxide pairs in these CuMnOx catalysts, the Cu-O-Mn sites in those CuMnOx catalysts with highly isolated or highly dispersed CuO species were found to be highly active. For CuO-Mn2O3 oxide pair catalysts, the highly isolated/dispersed CuO species in Mn2O3 framework is essential to achieve high activity.

A Predictive Physico-chemical Model of Biochar Oxidation

Pyrolysis of solid fuels forms a solid carbon-rich fuel, also called char, whose physico-chemical description is rather complex. Heterogeneous oxidation reactions take place during thermochemical conversion of char. The present work proposes a predictive detailed kinetic model, opening a new path for a deeper understanding of the char conversion process. This model considers porosity, surface area, density of surface sites, and their evolution along the conversion process. The chemical aspects of char oxidation are modeled assuming a carbonaceous bulk structure, surrounded by a variety of surface sites which represent the chemical functionalities typically present in such materials. The heterogeneous chemical reactions and their kinetic parameters are defined based on previous studies in the literature and by analogy to homogeneous gas-phase reactions of aromatic species. A mathematical framework is proposed to couple physical and chemical descriptions of the oxidation process. Although the proposed model benefits from experimental information, it is able to comprehensively describe the conversion rate of a broad range of carbonaceous materials such as carbon nanotubes, graphite, and chars only on the basis of their elemental composition. The proposed model represents a first step in exploring the explicit and coupled treatment given to the physical and chemical evolution of the fuel throughout its conversion, allowing us to consistently describe the particle evolution, opening a path for reliable models to manage the chemistry of char conversion.