Binary Oxidation Research Articles

MnOx catalysts supported on SBA-15 and MCM-41 silicas for a competitive VOCs mixture oxidation: In-situ DRIFTS investigations

The catalytic oxidation of different volatile organic compounds (VOCs) has been widely studied for several decades within the field of air depollution. However, there is still much to understand regarding the effects that these VOCs have on each other when they are blended together in the reaction mixture, as would be expected in many emissions. Herein, the catalytic oxidation of toluene and 2-propanol on supported manganese oxides under both single and binary VOCs oxidation conditions has been studied. We have found the catalyst activity for VOCs mineralization and its selectivity towards other by-products (i.e., acetone or propylene from 2-propanol) to be strongly dependent on the reaction conditions, the catalyst redox properties and support acidity. We have also assessed the promotion/inhibition effects derived from the VOCs mixture and proposed the reaction mechanism in each case by means of in-situ DRIFTS measurements.

Toluene and 2-propanol mixture oxidation over Mn2O3 catalysts: Study of inhibition/promotion effects by in-situ DRIFTS

Three Mn2O3 catalysts were synthetized by different methods, characterized and tested in toluene and 2-propanol (iPrOH) oxidation in single and binary component mixture. In single VOC media, the catalytic activity was strongly influenced by the specific surface area, low-temperature reducibility and active surface-oxygen species. In the binary VOCs mixture oxidation, light-off curves were shifted to lower temperatures, suggesting a promoting effect on the catalytic activity for toluene and iPrOH oxidation. The acetone production in binary mixture was also shifted to lower temperatures. The obtained results were rationalized based on the different polarity of the VOCs, the available adsorbed oxygen and the exothermic character of the VOCs combustion. These promoting effects were pointed out by in-situ DRIFTS measurements, in which the pre-adsorption of any of these two VOCs affected the adsorption/reaction of the other. For the first time, in-situ DRIFTS has been applied to elucidate the reaction mechanisms of the oxidation of toluene/2-propanol mixture on Mn2O3, which allowed to correlate the surface phenomena and the catalytic performance.

Characteristics of catalytic destruction of dichloromethane and ethyl acetate mixture over HxPO4-RuOx/CeO2 catalyst

Catalytic destruction is an ascendant technology for the abatement of volatile organic compounds (VOCs) originating from solvent-based industrial processes. The varied composition tends to influence each VOC's catalytic behavior in the reaction mixture. We investigated the catalytic destruction of multi-component VOCs including dichloromethane (DCM) and ethyl acetate (EA), as representatives from pharmaceutical waste gases, over co-supported HxPO4-RuOx/CeO2 catalyst. A mutual inhibitory effect relating to concentrations because of competitive adsorption was verified in the binary VOCs oxidation and EA posed a more negative effect on DCM oxidation owing to EA's superior adsorption capacity. Preferential adsorption of EA on acidic sites (HxPO4/CeO2) promoted DCM activation on basic sites (O2−) and the dominating EA oxidation blocked DCM's access to oxidation centers (RuOx/CeO2), resulting in boosted monochloromethane yield and increased chlorine deposition for DCM oxidation. The impaired redox ability of Ru species owing to chlorine deposition in turn jeopardized deep oxidation of EA and its by-products, leading to increased gaseous by-products such as acetic acid originating from EA pyrolysis. Notably, DCM at low concentration slightly promoted EA conversion at low temperatures with or without water, consistent with the enhanced EA adsorption in co-adsorption analyses. This was mainly due to that DCM impeded the shielding effect of hydrolysate deposition from rapid EA hydrolysis depending on the decreased acidity. Moreover, water benefited EA hydrolysis but decreased CO2 selectivity while the generated water derived from EA was likely to affect DCM transformation. This work may provide theoretical guidance for the promotion of applied catalysts toward industrial applications.

3D Self-Supported Binary PtCu Aerogel Boosted Methanol Oxidation

Precious metal aerogel has a broad application prospect in the field of fuel cell electrocatalysis because of its unique structure characteristics. In this work, Three-dimensional (3D) self-supporting porous PtCu aerogels have been successfully synthesized via a gelation strategy based on excess NaBH4. The mass activity of optimized PtCu aerogel in acid methanol solution is 6.56 times higher than that of JM-Pt/C. In addition, the optimized PtCu aerogel showed better stability than JM Pt/C. For the methanol oxidation reaction, the optimized PtCu aerogel still maintains the current density of 930 mA mg−1 Pt after 3600 s Chronoamperometric (CA) test. By X-ray photoelectron spectroscopy (XPS), we demonstrate the electron transfer between Cu and Pt. This would arouse the change of electronic state and atomic spacing on the surface of Pt and endow the PtCu aerogel with both prominent activity and excellent stability due to lattice stress and electron effect. This work provides a strategy for reasonable design high performance fuel cell electrocatalysts.

Sequential coagulation and heat activated persulfate-peroxide binary oxidation process for landfill leachate treatment

This study investigated a sequential treatment of landfill leachate including coagulation and binary oxidation. In the first step, the chemical coagulation process in which alum was used as a coagulant was applied to the leachate and the Box-Behnken design was used for process optimization. Operating parameters of the chemical coagulation process were coagulant dose, initial pH, and reaction time while the model response was color number (CN) removal. As a second step, a heat-activated persulfate-peroxide (PS/PO) binary oxidation process was applied to the leachate, which was subjected to chemical coagulation under optimized conditions. The effects of initial pH, reaction time, PS/PO ratio, and temperature on the removal of chemical oxygen demand (COD), UV254, and CN were determined. Control experiments were carried out depending on reaction time, kinetic studies were performed and rate constants were obtained. Based on removal efficiencies, binary processes were more effective than single processes. Reaction rates were directly proportional to temperature and inversely proportional to the initial pH. The optimum operating conditions of the PS/PS/Heat process were as follows; total oxidant dose 100 mM, initial pH 5, reaction time 120 min, and temperature 80 °C. Consequently, 82.2% COD, 94.4% UV254, and 97.9% CN removal efficiencies were achieved by combined coagulation-advanced oxidation processes. Moreover, scavenging experiments were carried out to determine the types of radicals involved in the process. Under optimum conditions, it was determined that both sulfate and hydroxyl radicals were involved in the PS/PO/Heat process; however, the dominant radical type was hydroxyl radicals.

Resolving diurnal dynamics of the chloroplastic glutathione redox state in Arabidopsis reveals its photosynthetically derived oxidation.

Plants are subjected to fluctuations in light intensity, and this might cause unbalanced photosynthetic electron fluxes and overproduction of reactive oxygen species (ROS). Electrons needed for ROS detoxification are drawn, at least partially, from the cellular glutathione (GSH) pool via the ascorbate-glutathione cycle. Here, we explore the dynamics of the chloroplastic glutathione redox potential (chl-EGSH) using high-temporal-resolution monitoring of Arabidopsis (Arabidopsis thaliana) lines expressing the reduction-oxidation sensitive green fluorescent protein 2 (roGFP2) in chloroplasts. This was carried out over several days under dynamic environmental conditions and in correlation with PSII operating efficiency. Peaks in chl-EGSH oxidation during dark-to-light and light-to-dark transitions were observed. Increasing light intensities triggered a binary oxidation response, with a threshold around the light saturating point, suggesting two regulated oxidative states of the chl-EGSH. These patterns were not affected in npq1 plants, which are impaired in non-photochemical quenching. Oscillations between the two oxidation states were observed under fluctuating light in WT and npq1 plants, but not in pgr5 plants, suggesting a role for PSI photoinhibition in regulating the chl-EGSH dynamics. Remarkably, pgr5 plants showed an increase in chl-EGSH oxidation during the nights following light stresses, linking daytime photoinhibition and nighttime GSH metabolism. This work provides a systematic view of the dynamics of the in vivo chloroplastic glutathione redox state during varying light conditions.

Pd-based catalysts promoted by hierarchical porous Al2O3 and ZnO microsphere supports/coatings for ethyl acetate highly active and stable destruction

Developing economical and active materials is of great significance for VOC purification. Here, hierarchical porous Al2O3 and ZnO microspheres (Al2O3-pm and ZnO-pm) were synthesized by a facile hydrothermal strategy. The urchin-like Al2O3-pm and flower-like ZnO-pm possess high specific surface area (especially; external surface area) obviously boost the dispersion of Pd with 29.3 % and 30.1 % over Pd/Al2O3-pm and Pd/ZnO-pm, respectively, over 3.4 times higher than those of commercial Al2O3- and ZnO-supported counterparts. Pd/Al2O3-pm possesses excellent activity and CO2 yield in ethyl acetate (EA) degradation, with TOF reaches 7.76 × 10−3 s−1 at 160 °C under GHSV of 50,000 h-1. Moreover, Pd/Al2O3-pm exhibits satisfied performance in EA-contained binary VOCs oxidation and has high long-term stability under both dry and humid conditions. Both Pd sites and Brønsted acid sites participated in reaction process and initially react with EA to form ethylene and ethanol, respectively. Larger amount Brønsted acid sites over Pd/Al2O3-pm promote ethanol formation and C-C cleavage, resulting in different CO2 yields and EA activation mechanisms. The coating greatly enhances Pd dispersion over Pd supported monolithic catalyst, endowing its desired activity and stability even with a much lower Pd loading. This work promotes the potential application of noble-metal-based monolithic materials in VOC degradation.

Neonicotinoids removal by associated binary, tertiary and quaternary advanced oxidation processes: Synergistic effects, kinetics and mineralization

The degradation of four representative neonicotinoids, namely Thiamethoxam, Imidacloprid, Acetamiprid and Thiacloprid, was carried out by the sequential association of different advanced oxidation processes, including Ozonation, Electro-chemical Oxidation, Ultrasound, Ultraviolet radiation, and their different possible associations. There are no published papers in the literature on the removal of this type of insecticides through these associated oxidation processes. Single oxidation processes did not achieve total pollutants removal in less than 3 h (only UV radiation treatment obtain a total removal of Thiamethoxan in 150 min, but with mineralization below 15% TOC). For double sequential processes, Electro-oxidation-Ozone treatment obtains a total removal of Imidacloprid in 120 min and an increase of mineralization to 50% TOC. Three or four sequential processes are recommended to improve degradation and mineralization rates in a significant way, Electro-oxidation-Ozone-UV treatment obtains a total removal of Thiamethoxan in 80 min with mineralization over 75% TOC. These results confirm important synergistic effects which were quantified. The global trend indicates that Thiamethoxam is the most oxidizable neonicotinoid, whereas Acetamiprid is the most recalcitrant compound. The degradation rate of each neonicotinoid followed pseudo-first-order kinetics and the different oxidation pathways were also quantified from a kinetic point of view.

Treatment of 1,4-dioxane and trichloroethene co-contamination by an activated binary persulfate-peroxide oxidation process.

The efficacy of a binary oxidant system, hydrogen peroxide (H2O2) and persulfate, was investigated for treatment of 1,4-dioxane (dioxane) and trichloroethene (TCE) co-contamination. Batch experiments were conducted to examine the catalytic efficiency of Fe2+ and NaOH-based activation, oxidant decomposition rates, contaminant degradation effectiveness, and competitive degradation effects. For NaOH activation, the oxidant decomposition rate was moderate and sustained during the entire test period of 96h. However, dioxane degradation was limited (~ 33%). Conversely, the oxidants were depleted within 24h for the Fe2+-activated system, and dioxane degradation was complete within 4h. The activation and radical generation processes were different between Fe2+ and NaOH activation. Both dioxane and TCE underwent complete degradation in the co-contaminant experiment. The results of this study indicate that the Fe2+-catalyzed binary hydrogen peroxide-persulfate oxidant system is effective for oxidation of the tested contaminants separately and as co-contaminants.

Sn@SnO2 attached on carbon spheres as additive-free electrode for high-performance pseudocapacitor

Utilization of metal oxide/supports interface structures could generate high- performance electrochemical materials for clean energy storage and conversion. However, designing the metal oxide/supports interfaces with highly enhanced conductivity and cycle durability remains a significant challenge. Here, we demonstrate an in-situ growth technique to synthesize a Sn/SnO2@C composite with nano-Sn species attached on surface of carbon spheres (denoted as Sn/SnO2@C) during the carbonization of a sol-gel precursors of tin (IV) tetrachloride pentahydrate (SnCl4·5H2O) and Resorcinol-Formaldehyde (Sn4+-RF) in N2. We investigate the nucleation and crystal growth of Sn/SnO2 from Sn4+-RF precursor to Sn/SnO2@C composite with the variation of the concentration of acid value and heat-treatment temperature. Sn/SnO2@C-(1.0, 800) composite as supercapacitor electrode achieves a maximum specific capacitance of 906.8 F g−1 at a scan rate of 1 mV s−1 in 6 M KOH solution, and an excellent cycle durability of 2000 cycles at 5 A g−1. The electrochemical performances demonstrate that charge storage occurs in Sn/SnO2@C mainly due to redox reactions between the binary oxidation states: Sn↔Sn(OH)62−(IV) in basic electrolyte, hierarchical porosity and Sn/SnO2@C distinct structure, which is formed in situ. The work provides new insights into the rational design of [email protected] composites electrode materials for pseudocapacitor and other electrochemical devices.

Electrochemical remediation of BPA in a soil matrix by Pd/Ti and RuO2/Ti electrodes

This study aimed to investigate the bisphenol A (BPA) degradation performance of an electrokinetic process coupled with Pd/Ti (PT) and RuO2/Ti (RT) binary metallic oxidation electrodes under a potential gradient of 2 Vcm−1 for 5 days. Fifteen experiments conducted with five processing fluids, namely deionized water (DW), Na2SO4, citric acid (CA), NaOH and NaCl, and two binary metallic oxidation electrodes, Pd/Ti and RT, were investigated in this study. Electroosmosis permeability of 3.2 × 10−6–4.7 × 10−6, 4.0 × 10−6–4.9 × 10−6, and 3.7 × 10−6–6.8 × 10−6 cm2 V−1 s−1 were observed in the electrokinetic system with Ti, PT, and RT electrodes, respectively. A significant detachment of the coated metals was observed in BMOEEK–PT system with Na2SO4, CA, and NaOH processing fluids. A higher BPA treatment efficiency of 52.2–67.3 % was found in the BMOEEK–RT system, which was 1.4–1.8 times greater than in the EK–Ti system with DW as the processing fluid. The best treatment efficiency was found in the system with NaCl as the processing fluid, which may mostly result from less detachment of the coated metal from electrode and increased hypochlorite (OCl−) generation in the anode reservoir. The primary treatment mechanism in the BMOEEK system with NaCl procession fluid was degradation by anodic oxidation. It was concluded that both the binary metallic electrode and processing fluid played key roles in enhancing the electrochemical degradation of BPA. The electrode characteristics (progressive cyclic voltammogram and SEM micrograph with EDAX), electrokinetic behavior (specimen pH and current density), and treatment mechanism were also discussed in this study.

Study on 1,2,3‐trichlorobenzene destruction in a binary (Na,K)2CO3 molten salt oxidation system

This work focused on the destruction of 1,2,3‐trichlorobenzene (1,2,3‐TCB) in a binary molten salt oxidation (MSO) system. The effects of MSO reactor temperatures, additive amounts of TCB, and salt mixture on destruction and removal efficiency (DRE) of TCB and chlorine retention efficiency (CRE) were investigated. The drained salt was characterized by X‐ray diffraction (XRD) analysis, and the reaction mechanism and pathway were proposed as well. The results showed that the DRE and CRE reached more than 99 and 95%, respectively, at temperatures above 900°C. The reaction by‐products included C6H6, CH4, and CO, while chlorinated species were not detected. Larger amounts of salt mixture meant prolonging the gas residence time and were helpful for reaction. When TCB loading increased from 5 to 25 g, the DRE decreased by 6, <1, and <1%, and the CRE also decreased. The XRD analysis of drained salt confirmed the capture of chlorine in TCB by the molten salt. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 65–69, 2014

Removal of Gaseous Ammonia in Pt-Rh Binary Catalytic Oxidation

In this study, the oxidation of ammonia (NH3) to form nitrogen was investigated by selective catalytic oxidation (SCO) over a Pt-Rh binary catalyst fabricated by the incipient wetness impregnation process in a tubular fixed-bed flow quartz reactor (TFBR). The catalysts were analysed by three-dimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic light-scattering (DLS), zeta potential measurements, and linear sweep voltammograms (LSV). At optimum conditions, namely, a temperature of 673 K and an oxygen content of 4%, nearly 100% of the NH3 was removed by catalytic oxidation over the Pt-Rh binary catalyst. The main product of the NH3-SCO process was N2. Additionally, for the freshly prepared Pt-Rh binary catalyst, three peaks (at 235/295 nm, 245/315 nm, and 240/365 nm) were observed via EEFM; however, the peak with the highest emission wavelength disappeared over time as Pt-Rh binary catalyst was exhausted by NH3. These results show that EEFM spectroscopy, which enhances intrinsic emission Pt clusters in the Pt-Rh binary catalyst, is an effective method for characterizing this catalyst in catalytic treatment systems. The UV-Vis absorption spectra revealed that the bands associated with such octahedral platinum (IV) species were observed at about 350 nm. Moreover, the LSV reversible redox ability may explain the significant activity of the catalysts.

Formation of Protective Cr<sub>2</sub>O<sub>3</sub> Scale at High Temperature and the Effect of Mass Transport in the Presence of Water Vapor

The formation of protective Cr2O3scale at high temperature was evaluated using Wagner’s theory of binary alloy oxidation. The results show that at 1073 K, around 9.8 wt% of Cr is required to form external Cr2O3scale, and 3.5wt% of Cr is needed to maintain the scale. Introduction of water vapor has shifted the critical Cr concentration to higher value. The effects of water vapor in increasing Cr critical concentration to form external Cr2O3scale was disscussed from view of oxygen permeablility and Cr diffusivity in the alloy. It is concluded that Cr diffusivity has negligible effect, while oxygen permeability increase with the presence of water vapor, thus increase the oxidation rate.

Combinatorial Discovery of Binary and Ternary Alloy Hydrazine Oxidation Catalysts for Direct Hydrazine Fuel Cells

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Crystallographic snapshots of the complete reaction cycle of nicotine degradation by an amine oxidase of the monoamine oxidase (MAO) family

FAD-linked oxidases constitute a class of enzymes which catalyze dehydrogenation as a fundamental biochemical reaction, followed by reoxidation of reduced flavin. Here, we present high-resolution crystal structures showing the flavoenzyme 6-hydroxy-l-nicotine oxidase in action. This enzyme was trapped during catalytic degradation of the native substrate in a sequence of discrete reaction states corresponding to the substrate-reduced enzyme, a complex of the enzyme with the intermediate enamine product and formation of the final aminoketone product. The inactive d-stereoisomer binds in mirror symmetry with respect to the catalytic axis, revealing absolute stereospecificity of hydrogen transfer to the flavin. The structural data suggest deprotonation of the substrate when bound at the active site, an overall binary complex mechanism and oxidation by direct hydride transfer. The amine nitrogen has a critical role in the dehydrogenation step and may activate carbocation formation at the α-carbon via delocalization from the lone pair to σ* C(α)-H. Enzymatically assisted hydrolysis of the intermediate product occurs at a remote (Psite) cavity. Substrate entry and product exit follow different paths. Structural and kinetic data suggest that substrate can also bind to the reduced enzyme, associated with slower reoxidation as compared to the rate of reoxidation of free enzyme. The results are of general relevance for the mechanisms of flavin amine oxidases.

A multiscale modelling study of Ni–Cr crack tip initial stage oxidation at different stress intensities

In this study, different scale analyses have been performed to understand the very beginning stage of the Ni–Cr(1 1 1) binary alloy surface oxidation mechanism. The finite elements method (FEM) has been applied to find the stress intensity effect on a compact tension (CT) specimen crack tip, and a 2-μm rectangular region has been prepared for the quasi-continuum (QC) model. The displacement load calculated by FEM was applied at the upper and lower boundaries of the QC model. The obtained atomic positions of the deformed crystal structure were considered for quantum chemical molecular dynamics (QCMD) analysis by placing water molecules on the surface. Water molecules dissociate on the top site followed by the quick diffusion of hydrogen atoms on the surface through the hollow sites. Hydrogen is easily transported into the lattice due to its small atomic size. Increases in stress intensity factor ( K) act to deform the structure, which augments oxygen penetration and reduces hydrogen diffusion time; as a consequence, changes in K result in an increase of metallic surface oxidation. Oxygen preferentially bonds with chromium to develop a protective passive film on the surface, and the quickly diffused hydrogen is trapped on the metal surface. Hydrogen bonds with the metal by receiving electrons and, therefore, works as an oxidant on the surface and weakens the metal atomic bond at the primary stage. Initially, the oxidized surface forms a strong bond with oxygen, resulting in the breakage of metal–metal bonds. Therefore, this hydrogen action enhances the very early stage surface oxidation.

The Effect of Water Vapor on High Temperature Oxidation of Fe-Cr Alloys at 1073 K

The effect of water vapor on high temperature oxidation was studied based on Wagner's theory of binary alloy oxidation. The oxidation of Fe-Cr alloys was carried out at 1073 K in dry and humid conditions. The oxidation was conducted in a closed apparatus at 1073 K and the oxygen partial pressure of 1.1 x 10 -14 Pa, which was fixed by a Fe/FeO buffer. To prepare the humid condition, Ar-5% H 2 gas mixture of 3 x 10 4 Pa was filled in the apparatus, which provided the water vapor pressure of 3.3 x 10 2 Pa. The transition of internal and external oxidation was observed in Fe-8Cr in the dry condition and in Fe-12Cr in the humid condition. Interdiffusion experiment of Fe/Fe-16Cr diffusion couples in dry and humid environments showed that the diffusion coefficient of Cr was not influenced by dissolved hydrogen. The oxygen permeability in α-Fe was determined by means of internal oxidation of Fe-5Cr alloy at 1073 K and the oxygen partial pressure of 1.1 x 10 -14 Pa in a dry and two humid conditions with water vapor of 1.1 x 10 2 Pa and 3.3 x 10 2 Pa. The oxygen permeability in humid condition increases by a factor of 1.4. Dissolved hydrogen increases the oxygen permeability, thus increases the minimum concentration of Cr to form external scales in humid conditions. The presence of dissolved hydrogen changes the oxide shape from discrete spherical particle to spike-like precipitates, which enhances the oxygen transport along the metal/oxide precipitates interface.

Effects of Ge concentration on SiGe oxidation behavior

The oxidation of SiGe layers grown by molecular beam epitaxy was studied. Auger depth profile showed that after oxidation, Ge was completely rejected from the oxide and Ge-rich layers were formed. However, the Ge concentration in the SiGe layer was found to play an important role in the formation of these Ge-Rich layers. For SiGe with Ge concentration below 50%, Si was preferentially oxidized and only one Ge-rich layer was formed at the oxide/substrate interface. On the other hand, for SiGe with Ge concentration above 50%, two Ge-rich layers were formed after oxidation with one at the oxide/substrate interface and the other at the oxide surface. X-ray photoelectron spectroscopy studies showed that Ge at the oxide/substrate interface is in elemental form, while Ge at the oxide surface is in an intermediate oxidized state. A classical binary alloy oxidation theory is employed to explain the overall oxidation behavior qualitatively.

Role of kinetic effects on metal partition at the alloy-scale interface during the oxidation of alloys

An alternative mass balance at the alloy-scale interface is proposed for the Wagner theory of binary alloy oxidation. A simple relation between the bulk composition of the alloy and the scale composition at the alloy-scale interface, ξ′, is derived in terms of the transport properties of the scale and the limit of application of the relation defined. There is good agreement between calculated and measured values of ξ′.