Distinguishing homogeneous advanced oxidation processes in bulk water from heterogeneous surface reactions in organic oxidation.

Clarifying the reaction pathways at the solid-water interface and in bulk water solution is of great significance for the design of heterogeneous catalysts for selective oxidation of organic pollutants. However, achieving this goal is daunting because of the intricate interfacial reactions at the catalyst surface. Herein, we unravel the origin of the organic oxidation reactions with metal oxide catalysts, revealing that the radical-based advanced oxidation processes (AOPs) prevail in bulk water but not on the solid catalyst surfaces. We show that such differing reaction pathways widely exist in various chemical oxidation (e.g., high-valent Mn3+ and MnOX) and Fenton and Fenton-like catalytic oxidation (e.g., Fe2+ and FeOCl catalyzing H2O2, Co2+ and Co3O4 catalyzing persulfate) systems. Compared with the radical-based degradation and polymerization pathways of one-electron indirect AOP in homogeneous reactions, the heterogeneous catalysts provide unique surface properties to trigger surface-dependent coupling and polymerization pathways of a two-electron direct oxidative transfer process. These findings provide a fundamental understanding of catalytic organic oxidation processes at the solid-water interface, which could guide the design of heterogeneous nanocatalysts.

Substitution of 2-oxoglutarate alters reaction outcomes of the Pseudomonas savastanoi ethylene-forming enzyme.

In seeding plants, biosynthesis of the phytohormone ethylene, which regulates processes including fruit ripening and senescence, is catalyzed by 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase. The plant pathogen Pseudomonas savastanoi (previously classified as: Pseudomonas syringae) employs a different type of ethylene-forming enzyme (psEFE), though from the same structural superfamily as ACC oxidase, to catalyze ethylene formation from 2-oxoglutarate (2OG) in an arginine dependent manner. psEFE also catalyzes the more typical oxidation of arginine to give L-Δ1-pyrroline-5-carboxylate (P5C), a reaction coupled to oxidative decarboxylation of 2OG giving succinate and CO2. We report on the effects of C3 and/or C4 substituted 2OG derivatives on the reaction modes of psEFE. 1H NMR assays, including using the pure shift method, reveal that, within our limits of detection, none of the tested 2OG derivatives is converted to an alkene; some are converted to the corresponding ß-hydroxypropionate or succinate derivatives, with only the latter being coupled to arginine oxidation. The NMR results reveal that the nature of 2OG derivatization can affect the outcome of the bifurcating reaction, with some 2OG derivatives exclusively favoring the arginine oxidation pathway. Given that some of the tested 2OG derivatives are natural products, the results are of potential biological relevance. There are also opportunities for therapeutic or biocatalytic regulation of the outcomes of reactions catalyzed by 2OG-dependent oxygenases by the use of 2OG derivatives.

A Q-learning method based on coarse-to-fine potential energy surface for locating transition state and reaction pathway.

Transition state (TS) on the potential energy surface (PES) plays a key role in determining the kinetics and thermodynamics of chemical reactions. Inspired by the fact that the dynamics of complex systems are always driven by rare but significant transition events, we herein propose a TS search method in accordance with the Q-learning algorithm. Appropriate reward functions are set for a given PES to optimize the reaction pathway through continuous trial and error, and then the TS can be obtained from the optimized reaction pathway. The validity of this Q-learning method with reasonable settings of Q-value table including actions, states, learning rate, greedy rate, discount rate, and so on, is exemplified in 2 two-dimensional potential functions. In the applications of the Q-learning method to two chemical reactions, it is demonstrated that the Q-learning method can predict consistent TS and reaction pathway with those by ab initio calculations. Notably, the PES must be well prepared before using the Q-learning method, and a coarse-to-fine PES scanning scheme is thus introduced to save the computational time while maintaining the accuracy of the Q-learning prediction. This work offers a simple and reliable Q-learning method to search for all possible TS and reaction pathway of a chemical reaction, which may be a new option for effectively exploring the PES in an extensive search manner.

Hydroxyl Defects-Mediated Hydrolytic Activation of Peroxydisulfate Under Nanoconfinement: Role of Lewis Basic Sites for Altering the Photosensitized Species and Pathways.

Herein, the pivotal mechanism of defect engineering-mediated triazine-based conjugated polymers (TCPs) is comprehensively elucidated for photosensitized activation of peroxydisulfate (PDS) under nanoconfinement by encapsulating the defective polymer framework into the nanochannel of SBA-15 (d-TCPs@SBA-15). The incorporated hydroxyl defects (-OH defects) substantially accelerate the accumulation of electrons at -OH defects, forming the Lewis basic sites. Due to the facilitated elongation of the S─O bond and reduced energy barrier of SO5* generation, the captured PDS undergo prehydrolysis process, oxidized into O2 - and 1O2 by surrounding h+, thereby setting apart from the conventional reductive activation of SO4 -/•OH generation occurred in pristine TCPs (p-TCPs). Crucially, this work represents a pioneering effort in exploring the PDS activation pathway upon the defective polymer under the nanoconfinement to leverage kinetic merits of slow photon effect and reactive oxygen species (ROSs) enrichment, and the novel prehydrolysis activation mechanism involved may catalyze the rational design of photocatalysts featuring Lewis-acid/base centers.

Synthesis, Structures and Photophysical Properties of Asymmetric Fulvene-[b]-fused BODIPYs.

Herein, we developed a one-pot procedure to synthesize novel fulvene-[b]-fused BODIPYs from α-(2-alkynylphenyl)-pyrrole and acylpyrrole, using 5-exo cyclization as the key transformation. Compared to benzene-[b]-fused BODIPYs, although they have similar chemical compositions, their structures and properties significantly differ from each other, which can be attributed to the less aromaticity of the fulvene linker than benzene. Notably, fulvene-[b]-fused BODIPY 1 b exhibits helical-twisted core skeleton, intensified red-shifted absorption, and peak fluorescence. In addition, the pathway of this one-pot reaction and the mechanism of POCl3 mediated 5-exo cyclization have been proposed by a combining experimental and computational study.

Reactivity, Pathways, and Iodinated Disinfection Byproduct Formation during Chlorination of Iodotyrosines Derived from Edible Seaweed.

Iodine derived from edible seaweed significantly enhances the formation of iodinated disinfection byproducts (I-DBPs) during household cooking. Reactions of chlorine with monoiodotyrosine (MIT) and diiodotyrosine (DIT) derived from seaweed were investigated. Species-specific second-order rate constants (25 °C) for the reaction of hypochlorous acid with neutral and anionic MIT were calculated to be 23.87 ± 5.01 and 634.65 ± 75.70 M-1 s-1, respectively, while the corresponding rate constants for that with neutral and anionic DIT were determined to be 12.51 ± 19.67 and 199.12 ± 8.64 M-1 s-1, respectively. Increasing temperature facilitated the reaction of chlorine with MIT and DIT. Based on the identification of 59 transformation products/DBPs from iodotyrosines by HPLC/Q-Orbitrap HRMS, three dominant reaction pathways were proposed. Thermodynamic results of computational modeling using density functional theory revealed that halogen exchange reaction follows a stepwise addition-elimination pathway. Among these DBPs, 3,5-diiodo-4-hydroxy-benzaldehyde and 3,5-diiodo-4-hydroxy-benzacetonitrle exhibited high toxic risk. During chlorination of MIT and DIT, iodinated trihalomethanes and haloacetic acids became dominant species at common cooking temperature (80 °C). These results provide insight into the mechanisms of halogen exchange reaction and imply important implications for the toxic risk associated with the exposure of I-DBPs from household cooking with iodine-containing food.

Combined Experimental and Density Functional Theory Study on the Mechanism of the Selective Catalytic Reduction of NO with NH3 over Metal-Free Carbon-Based Catalysts.

Metal-free carbon-based catalysts are attracting much attention in the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR). However, the mechanism of the NH3-SCR reaction on carbon-based catalysts is still controversial, which severely limits the development of carbon-based SCR catalysts. Herein, we successfully reconstructed carbon-based catalysts through oxidation treatment with nitric acid, thereby enhancing their low-temperature activity in NH3-SCR. Combining experimental results and density functional theory (DFT) calculations, we proposed a previously unreported NH3-SCR reaction mechanism over carbon-based catalysts. We demonstrated that C-OH and C-O-C groups not only effectively activate NH3 but also remarkedly promote the decomposition of intermediate NH2NO. This study enhances the understanding of the NH3-SCR mechanism on carbon-based catalysts and paves the way to develop low-temperature metal-free SCR catalysts.

Unraveling the Mechanistic Origin of High N2 Selectivity in Ammonia Selective Catalytic Oxidation on CuO-Based Catalyst.

NH3 emissions from industrial sources and possibly future energy production constitute a threat to human health because of their toxicity and participation in PM2.5 formation. Ammonia selective catalytic oxidation to N2 (NH3-SCO) is a promising route for NH3 emission control, but the mechanistic origin of achieving high N2 selectivity remains elusive. Here we constructed a highly N2-selective CuO/TiO2 catalyst and proposed a CuOx dimer active site based on the observation of a quadratic dependence of NH3-SCO reaction rate on CuOx loading, ac-STEM, and ab initio thermodynamic analysis. Combining this with the identification of a critical N2H4 intermediate by in situ DRIFTS characterization, a comprehensive N2H4-mediated reaction pathway was proposed by DFT calculations. The high N2 selectivity originated from the preference for NH2 coupling to generate N2H4 over NH2 dehydrogenation on the CuOx dimer active site. This work could pave the way for the rational design of efficient NH3-SCO catalysts.

Oxidation of selected fluoroquinolones by ferrate(VI) in water: Kinetics, mechanism, effects of constituents, and reaction pathways.

In this work, the oxidation of gatifloxacin (GAT), fleroxacin (FLE) and enoxacin (ENO) in aqueous solution by ferrate (Fe(VI)) was systemically investigated. Weak alkaline and high oxidant doses were favorable for the reaction. The pseudosecond-order rate constants were 0.18055, 0.29162, and 0.05476 L/(mg·min), and the activation energies were 25.13, 15.25, and 11.30 kJ/mol at pH = 8.00 and n(Fe(VI)):n(GAT) = 30:1, n(Fe(VI)):n(FLE) = 20:1, n(Fe(VI)):n(ENO) = 40:1 and a temperature of 25 °C. The maximum degradation rates of the GAT, FLE and ENO were 96.72%, 98.48% and 94.12%, respectively, well simulated by Response Surface Methodology. During the oxidation, the contribution of hydroxyl radicals (HO•) varied with time, whereas the final contribution was approximately 20% at 30 min. The removal efficiency was inhibited by anions by less than 10%, and cations by less than 25%, and significantly inhibited by high concentrations of humic acid. Moreover, two or three dominant reaction pathways were predicted, and the ring cleavages of quinolone and piperazine were mainly achieved through decarboxylation, demethlation and hydroxylation, and some pathways ended up with monocyclic chemicals, which were harmless to aquatic animals and plants. Theoretical calculations further proved that the reactions between FeO4- and neutral fluoroquinolone antibiotics were the major reactions. This work illustrates that Fe(VI) can efficiently remove fluoroquinolone antibiotics (FQs) in aqueous environments, and the results may contribute to the treatment of wastewater containing trace antibiotics and Fe(VI) chemistry.

Copper Selenophosphate, Cu3PSe4, Nanoparticle Synthesis: Octadecane Is the Key to a Simplified, Atom-Economical Reaction.

Nanoparticle syntheses are designed to produce the desired product in high yield but traditionally neglect atom-economy. Here we report that the simple, but significant, change of the solvent from 1-octadecene (1-ODE) to the operationally inert octadecane (ODA) permits an atom-economical synthesis of copper selenophosphate (Cu3PSe4) nanoparticles. This change eliminates the competing selenium (Se) delivery pathways from our first report that required an excess of Se. Instead Se0powder is dispersed in ODA, which promotes a formal eight-electron transfer between Cu3-xP and Se0. Powder X-ray diffraction and transmission electron microscopy confirm the purity of the Cu3PSe4, while 1H and 13C NMR indicate the absence of oxidized ODA or Se species. We utilize the direct pathway to gain insights into stoichiometry and ligand identity using thermogravimetric analysis and X-ray photoelectron spectroscopy. Given the prevalence of 1-ODE in nanoparticle synthesis, this approach could be applied to other chalcogenide reaction pathways to improve stoichiometry and atom-economy.

Controlling Phase Conversion of Cu-Sb-Se Nanoparticles through the Use of an Amide Base.

The family of copper antimony selenides is important for renewable energy applications. Several phases are accessible within narrow energy and compositional ranges, and tunability between phases is not well-established. Thus, this system provides a rich landscape to understand the phase transformations that occur in hot-injection nanoparticle syntheses. Rietveld refinements on X-ray diffraction patterns model anisotropic morphologies to obtain phase percentages. Reactions targeting the stoichiometry of CuSbSe2 formed Cu3SbSe3 before decomposing to thermodynamically stable CuSbSe2 over time. An amide base was added to balance cation reactivity and directly form CuSbSe2. Interestingly, Cu3SbSe3 remained present but converted to CuSbSe2 more rapidly. We propose that initial Cu3SbSe3 formation may be due to the selenium species not being reactive enough to balance the high reactivity of the copper complex. The unexpected effect of a base on cation reactivity in this system provides insight into the advantages and limitations for its use in other multivalent systems.

Boosting Low-Temperature CO2 Hydrogenation over Ni-based Catalysts by Tuning Strong Metal-Support Interactions.

Rational design of low-cost and efficient transition-metal catalysts for low-temperature CO2 activation is significant and poses great challenges. Herein, a strategy via regulating the local electron density of active sites is developed to boost CO2 methanation that normally requires >350 °C for commercial Ni catalysts. An optimal Ni/ZrO2 catalyst affords an excellent low-temperature performance hitherto, with a CO2 conversion of 84.0 %, CH4 selectivity of 98.6 % even at 230 °C and GHSV of 12,000 mL g-1 h-1 for 106 h, reflecting one of the best CO2 methanation performance to date on Ni-based catalysts. Combined a series of in situ spectroscopic characterization studies reveal that re-constructing monoclinic-ZrO2 supported Ni species with abundant oxygen vacancies can facilitate CO2 activation, owing to the enhanced local electron density of Ni induced by the strong metal-support interactions. These findings might be of great aid for construction of robust catalysts with an enhanced performance for CO2 emission abatement and beyond.

d-Electrons of Platinum Alloy Steering CO Pathway for Low-charge Potential Li-CO2 Batteries.

Aprotic Li-CO2 batteries suffer from sluggish solid-solid co-oxidation kinetics of C and Li2CO3, requiring extremely high charging potentials and leading to serious side reactions and poor energy efficiency. Herein, we introduce a novel approach to address these challenges by modulating the reaction pathway with tailored Pt d-electrons and develop an aprotic Li-CO2 battery with CO and Li2CO3 as the main discharge products. Note that the gas-solid co-oxidation reaction between CO and Li2CO3 is both kinetically and thermodynamically more favorable. Consequently, the Li-CO2 batteries with CoPt alloy-supported on nitrogen-doped carbon nanofiber (CoPt@NCNF) cathode exhibit a charging potential of 2.89 V at 50 µA cm-2, which is the lowest charging potential to date. Moreover, the CoPt@NCNF cathode also shows exceptional cycling stability (218 cycles at 50 µA cm-2) and high energy efficiency up to 74.6%. Comprehensive experiments and theoretical calculations reveal that the lowered d-band center of CoPt alloy effectively promotes CO desorption and inhibits further CO reduction to C. This work provides promising insights into developing efficient and CO-selective Li-CO2 batteries.

Calcination of sewage sludge-based sulphoaluminate cement clinker: Mineral formation mechanism and heavy metal transition behaviors.

Utilizing sewage sludge (SS) to calcinate sulphoaluminate cement (SAC) is a promising technology for low-carbon transition of cement industry, but the unclear effects of SS-contained heavy metals limit the application of this technology. In this study, the effects of SS addition on the calcination of SAC clinker and the transformation of heavy metals were studied from the aspects of mineral phase change, microstructure evolution and heavy metal speciation respectively, covering the mineral formation temperature 900-1250 °C. The results show that the added SS will reduce the formation temperature and change the reaction pathways of mineral phases. When the content of SS increases from 10% to 25%, the compositions of mesophases CaO·Al2O3 and 4CaO·2SiO2·CaSO4 increase by 6.33% and 9.73%, respectively. Meanwhile, the formation of minerals will solidify Zn, Ni, Mn, Cu, Cr, and convert them into a more stable fraction (residual fraction), indicating a lower probability to harm the environment. Moreover, heavy metals present different migration behaviors. After calcination, Mn migrates from SS to 4CaO·Al2O3·Fe2O3 (52.48%), while Zn prefers to enter 3CaO·3Al2O3·CaSO4 (43.74%) and 4CaO·Al2O3·Fe2O3 (38.06%). This study offers new insights into the mineral formation mechanism and heavy metal transition behaviors of sewage sludge-based SAC.

The origins of potentially superior properties and multifunctionalities of carbon-nano zero-valent iron in the carbonization pyrolysis process.

Although carbon-nano zero-valent iron (C@nZVI) composites with unique properties have been used for environmental remediation, the origins of their superior properties and multifunctionalities of C@nZVI still need to be verified. Here, iron precursor nanoparticles (PML-Fe NPs) synthesized by Pinus massoniana Lamb and carbonized C@nZVI were systemically compared to reveal the origins of the structure and performance of C@nZVI composites. Characterizations showed that structure-modulated C@nZVI has favorable properties of good crystallinity, graphite carbon-rich structure but also defects when compared to PML-Fe NPs. The resultant carbon layer fundamentally improved its dispersion and anti-oxidation properties. Further experiments demonstrated that the evolution of material crystallinity, graphitization and defects affected the reaction pathway of hexavalent chromium (Cr(VI)), oxytetracycline hydrochloride (OTC), and 17ß-estradiol (ßE2). The multifunctionalities covered adsorption, reduction and catalytic oxidation. This study explains the origins of multifunctional C@nZVI by understanding the structure-property correlation in the carbonization process.

A Spectroscopic Study on Nitrogen Electrooxidation to Nitrate.

As a potential substitute technique for conventional nitrate production, electrocatalytic nitrogen oxidation reaction (NOR) is gaining more and more attention. But, the pathway of this reaction is still unknown owing to the lack of understanding on key reaction intermediates. Herein, electrochemical in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotope-labeled online differential electrochemical mass spectrometry (DEMS) are employed to study the NOR mechanism over a Rh catalyst. Based on the detected asymmetric NO2 - bending, NO3 - vibration, N=O stretching, and N-N stretching as well as isotope-labeled mass signals of N2 O and NO, it can be deduced that the NOR undergoes an associative mechanism (distal approach) and the strong N≡N bond in N2 prefers to break concurrently with the hydroxyl addition in distal N.

Elaborated Reaction Pathway of Photothermal Catalytic CO2 Conversion with H2 O on Gallium Oxide-Decorated and -Defective Surfaces.

Ga2 O3 -decorated and -defective surface models based on anatase TiO2 have been established. The thermodynamic reaction pathways, including protonation, deoxygenation and hydroxylation steps, during CO2 conversion with H2 O to C1 products were calculated. The calculation results demonstrate that a Ga2 O3 cocatalyst enhances the selective adsorption of CO2 and slightly weakens the competitive adsorption of H2 O. The promotion effect of Ga2 O3 on the subsequent reaction depends on the availability of protons and electrons. Free-energy calculations revealed that the basic functional site generated by Ga2 O3 not only suppresses the back reaction of the OH group after H2 O directly provides protons but also maintains the surface defect oxygen vacancy (VO ), which promotes the reaction thermodynamics but tends to be consumed in the process. Additionally, Ga2 O3 decoration promotes VO formation, and the coexistence of Ga2 O3 and VO further decreases the reaction rate-determining step energy barrier, promoting C1 production.

Synthesis of liquid fuel via direct hydrogenation of CO2.

Synthesis of liquid fuels (C5+ hydrocarbons) via CO2 hydrogenation is very promising. Hydrogenation of CO2 to liquid hydrocarbons usually proceeds through tandem catalysis of reverse water gas shift (RWGS) reaction to produce CO, and subsequent CO hydrogenation to hydrocarbons via Fischer-Tropsch synthesis (FTS). CO2 is a thermodynamically stable and chemically inert molecule, and RWGS reaction is endothermic and needs a higher temperature, whereas FTS reaction is exothermic and is thermodynamically favored at a lower temperature. Therefore, the reported technologies have some obvious drawbacks, such as high temperature, low selectivity, and use of complex catalysts. Herein we discovered that a simple Co6/MnOx nanocatalyst could efficiently catalyze CO2 hydrogenation. The reaction proceeded at 200 °C, which is much lower than those reported so far. The selectivity of liquid hydrocarbon (C5 to C26, mostly n-paraffin) in total product could reach 53.2 C-mol%, which is among the highest reported to date. Interestingly, CO was hardly detectable during the reaction. The in situ Fourier transform infrared characterization and 13CO labeling test confirmed that the reaction was not via CO, accounting for the eminent catalytic results. This report represents significant progress in CO2 chemistry and CO2 transformation.

DFT Simulation-Based Design of 1T-MoS2 Cathode Hosts for Li-S Batteries and Experimental Evaluation.

The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides (LiPSs) caused by the rapid LiPSs migration to the anode and the slow reaction kinetics in the chain of LiPSs conversion. In this study, we explore 1T-MoS2 as a cathode host for Li-S batteries by examining the affinity of 1T-MoS2 substrates (pristine 1T-MoS2, defected 1T-MoS2 with one and two S vacancies) toward LiPSs and their electrocatalytic effects. Density functional theory (DFT) simulations are used to determine the adsorption energy of LiPSs to these substrates, the Gibbs free energy profiles for the reaction chain, and the preferred pathways and activation energies for the slow reaction stage from Li2S4 to Li2S. The obtained information highlights the potential benefit of a combination of 1T-MoS2 regions, without or with one and two sulphur vacancies, for an improved Li-S battery performance. The recommendation is implemented in a Li-S battery with areas of pristine 1T-MoS2 and some proportion of one and two S vacancies, exhibiting a capacity of 1190 mAh/g at 0.1C, with 97% capacity retention after 60 cycles in a schedule of different C-rates from 0.1C to 2C and back to 0.1C.

Microwave-Assisted Base-Free Oxidation of Glucose with H2O2 on Gold- and Manganese-Containing SBA-15-Insight into Factors Affecting the Reaction Pathway.

The aim of this work was to gain insights into the role of manganese in MnSBA-15 support for gold in the base-free glucose oxidation with H2O2 using a microwave reactor. MnSBA-15 (manganese-acidity source) and SBA-15 (for comparison) were modified with Au (2.2 wt. %) and Cu (for comparison). The physicochemical properties of the catalysts were investigated by XRD, N2 ads/des, TEM, UV-vis, XPS, pyridine adsorption combined with FTIR, ATR-FTIR, and 2-propanol decomposition. The effects of the Mn presence in the support, Au NPs size that determines the number of active Au centers, and the Fermi energy (EF), together with the effects of the pore size, reaction temperature, and time on the activity and selectivity of the applied catalysts were assessed and discussed. It has been demonstrated that the presence of Mn generated Lewis acid centers which did not participate in glucose and H2O2 adsorption, and thus, were not directly involved in the reaction pathway. Both reagents were adsorbed on gold nanoparticles. H2O2 was decomposed to molecular oxygen which oxidized glucose to gluconic acid (50-90% of glucose conversion depending on the reaction time and ~100% selectivity). The presence of manganese in MnSBA-15 was responsible for increased Au NPs size and only slightly influenced the negative charge on gold particles. To achieve effective activity a compromise between the number of active gold species and the level of EF has to be reached (for 5.7 nm Au NPs).