Oxygen Transfer Mechanism Research Articles

Atomically dispersed Fe-N4 sites in activation of peroxymonosulfate for wastewater purification: Mechanism of non-radical pathways and their quantification

Single-atom catalysts are promising alternatives to homogeneous and heterogeneous catalysts in the advanced oxidation processes for contaminant degradation; however, quantifying the exact contribution of nonradical reactive oxygen species has remained challenging. Herein, Fe single atoms anchored on nitrogen-doped carbonaceous substrates (Fe SAs-N-C) were synthesized for peroxymonosulfate (PMS) activation toward pollutant degradation. Fe SAs-N-C achieved high activity within 30 min, which is 17.20 and 5.08 times higher than those of N-C catalysts without or with Fe nanoparticles, respectively. A synergistic mechanism of singlet oxygen (1O2) and electron transfer for dominating pollutant degradation was revealed. The former contributed 78.50 % while the latter contributed 21.50 % in pollutant elimination. Density functional theory calculations uncovered that the O atom in −SO4 moiety of PMS was adsorbed on the Fe atoms, leading to the OH bond elongation and generating 1O2. While the absorbed O atom in OO bond near to −SO4 moiety of PMS tended to enlarge the OO bond and accelerate the electron transfer. The adsorbed PMS was prone to being decomposed into 1O2 due to a lower energy barrier (0.43 eV) of 1O2 rate-determining step than that of electron transfer (0.95 eV). Fe-N4 sites are both electron transfer channels and 1O2 formation sites. This work provides insights into the quantitative contributions of non-radical active species to pollutant degradation.

Prehydrated Electrons Activated by Continuous Electron Transfer Stemmed from Peracetic Acid Homolysis Mediated by Diamond Surface Defects for Enhanced PFOA Destruction.

Research on the use of peracetic acid (PAA) activated by nonmetal solid catalysts for the removal of dissolved refractory organic compounds has gained attention recently due to its improved efficiency and suitability for advanced water treatment (AWT). Among these catalysts, nanocarbon (NC) stands out as an exceptional example. In the NC-based peroxide AWT studies, the focus on the mechanism involving multimedia coordination on the NC surface (reactive species (RS) path, electron reduction non-RS pathway, and singlet oxygen non-RS path) has been confined to the one-step electron reaction, leaving the mechanisms of multichannel or continuous electron transfer paths unexplored. Moreover, there are very few studies that have identified the nonfree radical pathway initiated by electron transfer within PAA AWT. In this study, the complete decomposition (kobs = 0.1995) and significant defluorination of perfluorooctanoic acid (PFOA, deF% = 72%) through PAA/NC has been confirmed. Through the use of multiple electrochemical monitors and the exploration of current diffusion effects, the process of electron reception and conduction stimulated by PAA activation was examined, leading to the discovery of the dynamic process from the PAA molecule → NC solid surface → target object. The vital role of prehydrated electrons (epre-) before the entry of resolvable electrons into the aqueous phase was also detailed. To the best of our knowledge, this is the first instance of identifying the nonradical mechanism of continuous electron transfer in PAA-based AWT, which deviates from the previously identified mechanisms of singlet oxygen, single-electron, or double-electron single-path transfer. The pathway, along with the strong reducibility of epre- initiated by this pathway, has been proven to be essential in reducing the need for catalysts and chemicals in AWT.

Highly Efficient Catalytic Soot Combustion Over Potassium‐Promoted Pine Needles‐Like CoMnO Nanoarray Monolithic Catalysts

AbstractHerein, we report the high catalytic activity of the potassium‐promoted pine needles‐like Co2.7Mn0.3O4 nanoarray catalysts supported on the monolithic three‐dimensional macroporous (3‐DM) Ni foam substrate (xK/Co2.7Mn0.3O4−NF) by hydrothermal process and wet impregnation method for soot combustion. The 3‐DM structure of Ni foam and the macroporous nanostructure created by Co2.7Mn0.3O4 nano‐composites greatly improve the contact opportunities between soot particulates and catalysts. Our characterization results show that the addition of potassium promotes the mobility of oxygen species due to the low melting point of K‐containing compounds, and the strong interaction between potassium species and Co2.7Mn0.3O4 nano‐composites not only increases the number of active oxygen species but also improves the oxidizability of the xK/Co2.7Mn0.3O4−NF catalysts for soot oxidation. The impact of the K loadings on the catalysts displays a volcano‐type on the performance of soot oxidation and the catalyst loaded with 8 wt.% potassium species shows the highest activity with T50 at 314 °C in 600 ppm NO/O2/N2 flow, as well as high stability and water resistance. Simultaneously, the electron transfer and oxygen transfer mechanisms for soot combustion are discussed in detail. The strategy employed in this work has potential application prospects in other catalytic oxidation systems.

Bioinspired Non-Heme Mn Catalysts for Regio- and Stereoselective Oxyfunctionalizations with H2 O2.

In recent years, metalloenzymes-mediated highly selective oxidations of organic substrates under mild conditions have been inspiration for developing synthetic bioinspired catalyst systems, capable of conducting such processes in the laboratory (and, in the future, in industry), relying on easy-to-handle and environmentally benign oxidants such as H2 O2 . To date, non-heme manganese complexes with chiral bis-amino-bis-pyridylmethyl and structurally related ligands are considered as possessing the highest synthetic potential, having demonstrated the ability to mediate a variety of chemo- and stereoselective oxidative transformations, such as epoxidations, C(sp3 )-H hydroxylations and ketonizations, oxidative desymmetrizations, kinetic resolutions, etc. Furthermore, in the past few years non-heme Mn based catalysts have become the major platform for studies focused on getting insight into the molecular mechanisms of oxidant activation and (stereo)selective oxygen transfer, testing non-traditional hydroperoxide oxidants, engineering catalytic sites with enzyme-like substrate recognition-based selectivity, exploration of catalytic regioselectivity trends in the oxidation of biologically active substrates of natural origin. This contribution summarizes the progress in manganese catalyzed C-H oxygenative transformations of organic substrates, achieved essentially in the past 5 years (late 2018-2023).

Mechanisms of Sulfoxidation and Epoxidation Mediated by Iron(III)-Iodosylbenzene Adduct: Electron-Transfer vs. Oxygen-Transfer Mechanism.

The mechanisms of sulfoxidation and epoxidation mediated by previously synthesized and characterized iron(III)-iodosylbenzene adduct, FeIII(OIPh) were investigated using para-substituted thioanisole and styrene derivatives as model substrates. Based on detailed kinetic reaction experiments, including the linear free-energy relationships between the relative reaction rates (logkrel) and the σp (4R-PhSMe) with ρ = -0.65 (catalytic) and ρ = -1.13 (stoichiometric), we obtained strong evidence that the stoichiometric and catalytic oxidation of thioanisoles mediated by FeIII(OIPh) species involves direct oxygen transfer. The small negative slope -2.18 from log kobs versus Eox for 4R-PhSMe gives further clear evidence for the direct oxygen atom transfer mechanism. On the contrary, with the linear free-energy relationships between the relative reaction rates (logkrel) and total substituent effect (TE, 4R-PhCHCH2) parameters with slope = 0.33 (catalytic) and 2.02 (stoichiometric), the stoichiometric and catalytic epoxidation of styrenes takes place through a nonconcerted electron transfer (ET) mechanism, including the formation of the radicaloid benzylic radical intermediate in the rate-determining step. On the basis of mechanistic studies, we came to the conclusion that the title iron(III)-iodosylbenzene complex is able to oxygenate sulfides and alkenes before it is transformed into the oxo-iron form by cleavage of the O-I bond.

ZnO–TiO2 Nanoparticles Coated by the Dioxomolybdenum (VI) bis-Schiff Base Complex for Catalytic Oxidation of Sulfides

The oxygenation processes for the organic compounds have great applications in fine organic fabrications. To speed up progress in the industrialization of such oxidation systems, a monometallic dioxomolybdenum (VI) bis-Schiff base complex (MoO2L2) was synthesized through coordination of easily accessible 4-hydroxyiminophenol ligand (HL) with cis-MoO22+ ion in an octahedral geometry. The structural conformation of MoO2L2 and its coordinated ligand (HL) was determined using modern spectrophotometric tools. A heterogeneous catalyst (MoO2L2@ZnO–TiO2) was successfully prepared by immobilization of MoO2L2 on the surface of ZnO–TiO2 nanostructured particles through the deprotonation of 4-OH group in its coordinated ligand. Various analytical techniques were used to examine the surface morphology and internal structure features of ZnO–TiO2 and MoO2L2@ZnO–TiO2 nanocomposites. To study the catalytic efficiency of MoO2L2 and MoO2L2@ZnO–TiO2-based catalysts, they were employed in the oxygenation process of Ph2S (diphenyl sulfide) and MePhS (methylphenyl sulfide) using the most environmentally friendly oxidant (an aqueous H2O2) under an aerobic environment. A high degree of selectivity was observed for the productivity of diphenyl sulfoxide (Ph2SO) and methylphenyl sulfoxide (MePhSO), with some contamination of overoxidation side products (Ph2SO2 and MePhSO2). The catalytic oxidative ability was not observably superior for the heterogeneous coated catalyst by ZnO–TiO2 over its homogeneous one (MoO2L2) due to the less redox activity of ZnO and TiO2 nanoparticles in the catalytic cycles for the oxygen-transfer mechanism. Both catalysts were successfully recycled, in which the homogeneous catalyst sustained its high catalytic potential for up to three cycles, while the heterogeneous catalyst was able to be reused up to six times.

Investigation for Oxygen Transfer Mechanism During Gas Tungsten Arc Welding with Carbon Dioxide Gas

Investigation for Oxygen Transfer Mechanism During Gas Tungsten Arc Welding with Carbon Dioxide Gas

Highly-efficient peroxydisulfate activation by polyaniline-polypyrrole copolymers derived pyrolytic carbon for 2,4-dichlorophenol removal in water: Coupling mechanism of singlet oxygen and electron transfer

Carbonization of N-containing aromatic polymers is a promising route to prepare N-doped carbon materials with low cost, easy regulation, and no external N source. However, there are relatively few studies applying these materials for persulfate activation, and the catalytic mechanisms of the existing reaction systems are divergent. In this paper, a series of N-doped carbon materials were prepared by carbonizing polyaniline (PANI), polypyrrole (PPy), and PANI-PPy copolymers. The copolymer-derived carbon materials exhibit superior peroxydisulfate (PDS) catalytic activity compared to some commercially available and reported carbon materials. Combing quenching experiments, EPR analysis, chemical probe analysis, and various electrochemical analysis methods identified the singlet oxygen (1O2) and electron transfer as the main reaction pathways of all systems, but the contribution of each pathway was influenced by the types of precursors. The structure-activity relationship indicated that the carbonyl group (CO) was the main active site for the 1O2 pathway, while the electron transfer ability of the reaction system and the potential of the complex formed by catalyst and PDS jointly determined the electron transfer pathway. This paper provides a new strategy for obtaining excellent N-doped carbon-based persulfate activators and deepens the insight into the mechanism of PDS activation by N-doped carbon materials.

Iron based oxygen-carrier-aided oxy-fuel combustion of coal char: Reactivity and oxygen transfer mechanism

Adding an active oxygen carrier to the inert bed material may favor the oxygen distribution in fluidized bed (FB) combustors. This so-called method “Oxygen-carrier-aided combustion, OCAC” has been applied recently to air combustion in FB boilers, but could also be potentially interesting in oxy-fuel combustion. Here we analyze OCAC in oxy-fuel combustion by experimental determination of the reactivity of char from three coals (lignite, bituminous and anthracite coal) using three oxygen carriers (OC, analytical reagent Fe2O3, hematite, and steel slag). The tests were conducted in a micro thermo-gravimetric analyzer (micro-TGA) and the combustion kinetics was determined for the nine combinations of char and OC. Additional tests were conducted in a macro-TGA i.e., much sample in a big ceramic crucible, to evaluate the phase composition and crystal quality using X-ray diffraction (XRD) to the combustion residues collected at various degrees of carbon conversion (0.2, 0.5, and 0.8). The results show that the burnout temperature decreases with OCs as the combustion rate increases, while the ignition temperature hardly changes. The enhancement of the rate of char combustion by OCs is in the following order: steel slag < hematite < AR-Fe2O3. The lower the fuel rank, the stronger the effect of the oxygen carrier. The combustion kinetics of chars using OC has a higher activation energy and pre-exponential factor than pure char. The enlarged lattice constant of Fe2O3 measured by XRD during the char combustion indicates that the redox reactions of Fe2O3 accelerate the oxidization of char by enhancing the rate of oxygen transport to the carbon surface.

Mixed oxidation of chlorophene and 4-tert-butylphenol by ferrate(VI): Reaction kinetics, cross-coupling products and improved utilization efficiency of ferrate(VI)

As two representative phenolic pollutants, chlorophene (CP) and 4-tert-butylphenol (4-tBP) are used in large quantities and could have adverse effects on aquatic organisms and even human health. Due to their co-occurrence in water and wastewater, the oxidative degradation of mixed solution of the two phenols by ferrate (Fe(VI)) was systematically investigated in this work. Compared with the single solution, the kapp values of CP and 4-tBP were increased by 15.7% and 91.9%, respectively in the mixed solution, and the calculated reaction stoichiometric efficiency (RSE) was also improved by more than one time. The reaction intermediates were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, from which three possible pathways including direct oxidation, oxygen transfer, ring opening and coupling reaction were proposed for mixed transformation of CP and 4-tBP in Fe(VI) system. The single/double oxygen transfer and single-electron transfer mechanism for the corresponding formation of hydroxylation products and coupling products from CP and 4-tBP were further elucidated by density functional theory (DFT) calculations. Since the cross-coupling reaction was more prone to occur than self-coupling reaction, the addition of another phenol promoted the conversion of the original phenol, leading to the increased kapp values of the two phenols in mixture solution. Finally, the salt bridge experiment also confirmed that the electron transfer between organic pollutants and Fe(VI) was enhanced in mixture solution of phenols. Findings of this study may provide useful information for eliminating co-existing water contaminants by Fe(VI).

Gas transfer model for a multistage vortex aerator: A novel oxygen transfer system for dissolved oxygen improvement

A novel aerator for enhancing the oxygen transfer rate and efficiency, named multistage vortex aerator (MVA), was developed. It uses vortex flow in repeated stages to increase the gas-liquid interfacial area and to decrease the thickness of the stagnant layer at the interface between the two phases. The basic characteristics of oxygen transfer using this aerator were investigated using the American Society of Civil Engineers standard procedure. The MVA could rapidly transfer oxygen to water to a concentration higher than 40 mg/L in 60 min owing to the effect of high purity oxygen, additional pressure induced by water and gas, and vortex flow dynamics. A gas transfer model was developed for describing the non-steady state operation of the aerator. This model is based on the mass and molar balances of oxygen in gas and water. It could successfully simulate the DO change inside the aerator. This study can help better understand the oxygen transfer mechanism and evaluate the performance of the new aerator at the various temperatures, pressures, and gas compositions found in diverse environmental systems.

Study on the co-pyrolysis of oil shale and corn stalk: Pyrolysis characteristics, kinetic and gaseous product analysis

Co-pyrolysis of oil shale and biomass can promote thermal decomposition and improve product quality because of the interaction. Therefore, the co-pyrolysis characteristics of oil shale (OS) and corn stalk (CS) were investigated by the combination of TG-FTIR-MS study. TG/DTG results showed that the decomposition of cellulose was promoted during co-pyrolysis, and the decomposition temperature of OS was advanced, while the decomposition rate decreased. Kinetic analysis showed that the lowest apparent activation energy occurred at a CS blending ratio of 50%. MS and FTIR showed that co-pyrolysis impeded the release of oxygen-containing gases, especially H2O and CO2 after 400 °C. The oxygen transfer mechanism is also applicable to OS and CS co-pyrolysis, which means the intermediate formed by the combination of alkali metal released from CS and C-O in OS has catalytic effect after chemisorbing H2O and CO2, leading to easier bond breaks in OS and re-release of partial H2O and CO2.

Oxygen Transfer Mechanism of ESR-Slag at Different Atmospheric Oxygen Contents

Oxygen Transfer Mechanism of ESR-Slag at Different Atmospheric Oxygen Contents

Application of MnCeOx supported on palygorskite and Al(OH)3 for HCHO oxidation: Catalytic performance and stability

Indoor formaldehyde (HCHO) is an important air pollutant, while it is very difficult to reduce HCHO to low-level (e.g. <0.08 mg/m3). Catalytic oxidation at ambient temperature has been increasingly recognized as one of the important methods to mitigate HCHO pollution due to its good effectiveness, stability, and recyclability. To further improve the activity of catalytic oxidation, this study develops the integrated MnCeOx catalysts supported on palygorskite (Pal) and aluminium hydroxide (Al(OH)3). Our results indicate that the synergistic interaction in MnCeOx through the oxygen transfer mechanism from the oxygen reservoir CeO2 to MnOx significantly improves the activity. Pal, Al(OH)3, etc. were applied as the supports with a focus on their dispersion, microstructure, strength, and relative role. MnCeOx can be anchored on the surface of Al(OH)3 with high dispersion. With the integrated catalyst, HCHO concentration decreases from 1.012 to 0.086 mg/m3 within 48 h. Higher oxidation activity of MnCeOx powder may be ascribed to the amount of active components on the surface. The incorporation of ZSM–5 and activated carbon can improve the adsorption of HCHO, and all integrated catalysts exhibit stronger activities, with HCHO being degraded to the level lower than 0.08 mg/m3. Meantime, the samples exhibit good stability and strength (20.2 MPa) without obvious decrease over five consecutive stability experiments.

Computational Survey of Recent Experimental Developments in the Hydroxylation Mechanism of Kynurenine 3-Monooxygenase.

Recently, two new mechanistic proposals for the kynurenine 3-monooxygenase (KMO) catalyzed hydroxylation reaction of l-Kynurenine (l-Kyn) have been proposed. According to the first proposal, instead of the distal oxygen, the proximal oxygen of the hydroperoxide intermediate of flavin adenine dinucleotide (FAD) is transferred to the substrate ring. The second study proposes that l-Kyn participates in its base form in the reaction. To address these proposals, the reaction was reconsidered with a 386 atom quantum cluster model that is based on a recent X-ray structure (PDB id: 6FOX). The computations were carried out at the UB3LYP/6-311+G(2d,2p)//UB3LYP/6-31G(d,p) level with solvation (polarizable continuum model) and dispersion (DFT-D3(BJ)) corrections. To supplement the results of the density functional theory (DFT) calculations, molecular dynamics (MD) simulations of the protein-substrate complex were employed. The comparison of a proximal oxygen transfer mechanism to the distal oxygen transfer mechanism revealed that the former requires too high of a barrier energy while the latter validated our previous results. According to the MD simulations, the hydroperoxy moiety does not favor an alignment that might promote the proximal oxygen transfer mechanism. In the second part of the study, hydroxylation reaction with the base form of l-Kyn was sought. Although DFT calculations confirmed a much more facile reaction with the base form of l-Kyn, a mechanism which would allow the deprotonation of the l-Kyn before the oxygen transfer could not be determined with the X-ray-based positions. A concerted mechanism with both the oxygen transfer and the deprotonation required a high barrier energy. A stepwise mechanism involving the deprotonation of l-Kyn was found, starting from an MD frame. The overall barrier of the oxygen transfer step of this model was found to be in the range of that of with neutral l-Kyn. MD simulations supported the idea of ineffectiveness of the nearby shell surrounding the utilized active site core on the deprotonation of l-Kyn.

Activation of H2O2 over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates

Zr-monosubstituted Lindqvist-type polyoxometalates (Zr-POMs), (Bu4N)2[W5O18Zr(H2O)3] (1) and (Bu4N)6[{W5O18Zr(μ-OH)}2] (2), have been employed as molecular models to unravel the mechanism of hydrogen peroxide activation over Zr(IV) sites. Compounds 1 and 2 are hydrolytically stable and catalyze the epoxidation of C═C bonds in unfunctionalized alkenes and α,β-unsaturated ketones, as well as sulfoxidation of thioethers. Monomer 1 is more active than dimer 2. Acid additives greatly accelerate the oxygenation reactions and increase oxidant utilization efficiency up to >99%. Product distributions are indicative of a heterolytic oxygen transfer mechanism that involves electrophilic oxidizing species formed upon the interaction of Zr-POM and H2O2. The interaction of 1 and 2 with H2O2 and the resulting peroxo derivatives have been investigated by UV–vis, FTIR, Raman spectroscopy, HR-ESI-MS, and combined HPLC-ICP-atomic emission spectroscopy techniques. The interaction between an 17O-enriched dimer, (Bu4N)6[{W5O18Zr(μ-OCH3)}2] (2′), and H2O2 was also analyzed by 17O NMR spectroscopy. Combining these experimental studies with DFT calculations suggested the existence of dimeric peroxo species [(μ-η2:η2-O2){ZrW5O18}2]6– as well as monomeric Zr-hydroperoxo [W5O18Zr(η2-OOH)]3– and Zr-peroxo [HW5O18Zr(η2-O2)]3– species. Reactivity studies revealed that the dimeric peroxo is inert toward alkenes but is able to transfer oxygen atoms to thioethers, while the monomeric peroxo intermediate is capable of epoxidizing C═C bonds. DFT analysis of the reaction mechanism identifies the monomeric Zr-hydroperoxo intermediate as the real epoxidizing species and the corresponding α-oxygen transfer to the substrate as the rate-determining step. The calculations also showed that protonation of Zr-POM significantly reduces the free-energy barrier of the key oxygen-transfer step because of the greater electrophilicity of the catalyst and that dimeric species hampers the approach of alkene substrates due to steric repulsions reducing its reactivity. The improved performance of the Zr(IV) catalyst relative to Ti(IV) and Nb(V) catalysts is respectively due to a flexible coordination environment and a low tendency to form energy deep-well and low-reactive Zr-peroxo intermediates.

Tingkat Difusi Oksigen Selama Periode Blind Feeding Budidaya Intensif Udang Vaname (Litopenaeus vannamei)

The diffusion process is a limiting factor that key plays for the oxygen transfer mechanism in the pond water column. The purpose of this study was to determine of oxygen diffusion rate during the blind feeding period of intensive shrimp culture of vaname (L. vannamei). This research was conducted for 30 days blind feeding period of intensive vaname shrimp culture, the research using concept of ex-pose facto causal design. Furthermore, the oxygen diffusion rate is calculated mathematically and a regression test is carried out on the associated water quality parameters. During the blind feeding period, the oxygen diffusion rate fluctuates and dynamically, with a diffusion rate ranging from 0.015-0.028 mgO 2 /L/hour. This condition is followed by a stabilizing and optimum condition of pond water quality parameter values throughout in the aquaculture. Diurnal periodically, the oxygen diffusion mechanism has an influence on the level of oxygen solubility in ponds. This relationship is modeled by the equation Y = 0.006 + 0.002x. This means that for each diffusion transfer increase of 1 mgO 2 /L/hour, there will be an oxygen increase in the ponds of 0.002 mg/L. The conclusion of this study is that the oxygen diffusion rate during the blind feeding period of intensive vaname shrimp culture obtained an average at 0.020 mgO 2 /L/hour, ranging from 0.018-0.023 mgO 2 /L/hour for 30 days of culture. From the results of this study, it is hoped that research can be developed study regarding of mechanisms, dynamics, and the effect of oxygen diffusion on the intensive shrimp farming ecology.

Mechanism and kinetics of the aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by cobalt porphyrin in a membrane microchannel reactor

The highly efficient selective aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by cobalt porphyrin was achieved in a membrane microchannel reactor. The efficiency of benzyl alcohol oxidation was remarkably improved in the micro-structured chemical system, achieving a conversion and benzaldehyde selectivity of 82% and 98%, respectively, in 6.5 min. The classification and transfer of free radicals, as well as the oxygen-transfer mechanism, were determined by in situ EPR (electron paramagnetic resonance) and in situ UV–visible spectroscopy. Further kinetic studies revealed that the oxidation of benzyl alcohol follows the Michaelis–Menten kinetics, with Km = 0.133 mol/L.A mathematic kinetic model was proposed, and the kinetic model fitted the experimental data well. The mathematical model can predict the reaction process at a wide range of benzyl alcohol concentrations, which is beneficial for the process optimization and reactor design.

Исследование массотранспортных потерь структурно-модифицированных электродов воздушно-водородных топливных элементов методом вольт-амперной характеристики

The article discusses platinum-carbon electrodes with mixed conductivity as part of membrane-electrode assemblies of fuel cells containing structural-modifying additives with structural elements of various types: carbon nanotubes with elongated structural elements and graphene-like materials with almost two-dimensional planes. Based on the data on the limiting current density obtained in potentiodynamic and potentiostatic modes, the mass transport losses of molecular oxygen transfer in these electrodes are investigated. Using different measurement conditions, the baric dependences of the current density were constructed, the limiting factors and mechanisms of oxygen transfer in the studied structures and the role of the introduced modifiers were clarified.

Valorizing petroleum coke into hydrogen-rich syngas through K-promoted catalytic steam gasification

Hydrogen-rich syngas was successfully produced from catalytic steam gasification of petroleum coke. This work studied the steam gasification of petroleum coke over KOH, K2CO3, KNO3, CaO, Fe2O3, K2CO3–CaO and K2CO3–Fe2O3 in a pressurized fixed bed. KOH and K2CO3 demonstrated good catalytic activity compared with other catalysts. The carbon conversion efficiency (CCE) increased from 14.7 wt% to 61.4 wt% and 87.9 wt% after adding 10 wt% K2CO3 and 10 wt% KOH, respectively, and H2 content increased from 60.9 vol% to 66.7 vol% and 64.2 vol%. The increase of gasification temperature and pressure resulted in the increase of CCE. However, raising temperature was beneficial to the increase of H2 and CO contents, while the elevated pressure was in favor of the formation of CH4. In addition, the K-catalytic steam gasification of petroleum coke accorded with the oxygen transfer and intermediate hybrid mechanism.