Higher Oxidation Efficiency Research Articles

Investigation of catalytic mechanism of formaldehyde oxidation over three-dimensionally ordered macroporous Au/CeO2 catalyst

A colloidal crystal template method coupled with a precursor complexion process was developed to create three-dimensionally ordered macroporous (3DOM) Au/CeO2 catalyst. The resultant Au/CeO2 catalyst possesses well-defined 3DOM structure, and shows enhanced catalytic performance for formaldehyde (HCHO) oxidation with 100% HCHO conversion at ∼75°C. The catalytic mechanism of HCHO catalytic oxidation over 3DOM Au/CeO2 catalyst was systematically investigated by means of gas chromatograph (GC), H2-temperature programmed reduction (H2-TPR), temperature programmed surface reaction (TPSR), CO2-temperature programmed desorption (TPD), and Fourier transform infra-red (FT-IR) spectroscopy. GC results indicate that HCOOH intermediate is generated during HCHO catalytic oxidation. TPD and TPSR tests show that the weak absorption ability of CO2 over 3DOM Au/CeO2 catalyst and the existence of Au active species in ionic and metallic states in 3DOM Au/CeO2 catalyst largely improve the catalytic activity, favoring the enhanced HCHO catalytic oxidation. FT-IR tests prove that the carbonate and hydrocarbonate formed on the surface of 3DOM Au/CeO2 catalyst during HCHO catalytic oxidation may account for its deactivation. Based on the above investigation, a new catalytic mechanism of enhanced HCHO catalytic oxidation over 3DOM Au/CeO2 catalyst is proposed. The mechanism may afford the scientific guidance for preparing high efficiency oxide supported noble metal catalysts and present a solution for solving their deactivation problem.

An efficient and energy saving approach to photocatalytic degradation of opaque high-chroma methylene blue wastewater by electrocatalytic pre-oxidation

The opaque methylene blue (MB) dye wastewater hard to be degraded directly by photocatalytic (PC) oxidation was successfully decomposed by a new two-step process, in which electrocatalytic (EC) pre-oxidation was followed with photoelectric synergistic catalytic (PEC) oxidation. The SnO 2/TiO 2 NTs electrode was used as the anode, which simultaneously has superior EC and PC performance. In the pre-oxidation step, the opaque dye wastewater is decolorized by EC oxidation, and the wastewater becomes a light transmission system, which provides the necessary condition for PC oxidation. However, the individual EC oxidation will be of low current efficiency and high energy consumption for the decreasing of the pollutants concentration in wastewater. Thus, in second stage, the PC process was introduced, and the synergistic catalytic oxidation leads to high PEC oxidation efficiency, so that the complete mineralization of the MB dye wastewater was realized. The whole process is highly efficient and energy-saving, which opens a new avenue to degrade the high-chroma or opaque dye wastewater.

High efficient electrocatalytic oxidation of formic acid at Pt dispersed on porous poly( o-methoxyaniline)

A Pt-based composite electrode material has been developed by dispersing Pt nanoparticles on a porous poly( o-methoxyaniline) (POMA) film, which was produced via electropolymerization on a glassy carbon (GC) electrode. As-formed Pt/POMA/GC electrode was characterized by SEM, EDX and electrochemical analysis. Furthermore, the composite electrode material was evaluated by its electrocatalytic performance for formic acid oxidation using cyclic voltammetry and chronoamperometry methods. Compared to Pt deposited on bare GC (Pt/GC), Pt/POMA/GC exhibits higher catalytic activity and stronger poisoning-tolerance ability towards formic acid electro-oxidation. The improved performance is attributed to the synergetic effect between Pt and POMA. Also, as demonstrated by CO stripping voltammograms, the interference of CO on Pt/POMA/GC is greatly weakened. These results suggest that the POMA film has great potential to serve as a promising support material for the electrocatalytic oxidation of formic acid.

Acceleration of Ethanol Electro-Oxidation on a Carbon-Supported Platinum Catalyst at Intermediate Temperatures

The performance of a direct ethanol fuel cell is expected to improve at relatively high temperatures. In this study, the electro-oxidation of ethanol on a carbon-supported platinum catalyst (Pt/C) at intermediate temperatures (235–260°C) was investigated using a single cell fabricated with the CsH2PO4 proton conducting solid electrolyte. The main products of ethanol electro-oxidation at intermediate temperatures were H2, CO2, and CH4 while the formation of C2 compounds was much small in comparison with the gaseous products even at a high ethanol concentration (i.e., water/ethanol molar ratio = 3). An analysis of the reaction products revealed that the C–C bond dissociation ratio of ethanol is higher than 90% at intermediate temperatures. In addition, a high current efficiency for the total oxidation of ethanol (ca. 80%) was observed. The apparent activation energy for this ethanol oxidation suggests reaction paths for the formation of CO2: the C–C bond dissociation or the subsequent oxidation of the adsorbed CHx species is thought to be rate-determining at intermediate temperatures. These observations clearly demonstrate the advantages of the efficient and direct use of ethanol at intermediate temperatures.

Technique for complete oxidation of organic compounds in supercritical water

Results are presented of tests of a pilot stationary installation for supercritical water oxidation of organic compounds, first created in Russia. A high oxidation efficiency of nitro compounds formed as waste in manufacture of explosives is demonstrated.

CHO Oxidation from a CHO Gel Compared with a Drink during Exercise

Recently, it has been shown that ingestion of solutions with glucose (GLU) and fructose (FRC) leads to 20%–50% higher CHO oxidation rates compared with GLU alone. Although most laboratory studies used solutions to deliver CHO, in practice, athletes often ingest CHO in the form of gels (semisolid). It is currently not known if CHO ingested in the form of a gel is oxidized as effectively as a drink. To investigate exogenous CHO oxidation from CHO provided in semisolid (GEL) or solution (DRINK) form during cycling. Eight well-trained cyclists(age = 34 ± 7 yr, mass = 76 ± 9 kg, VO2max = 61 ± 7 mL·kg−¹·min−¹) performed three exercise trials in random order. The trials consisted of cycling at 59% ± 4% VO2max for 180 min while receiving one of the following three treatments: GEL plus plain water, DRINK, or plain water. Both CHO treatments delivered GLU plus FRC in a ratio of 2:1 at a rate of 1.8 g·min−¹ (108 g·h−¹). Fluid intake was matched between treatments at 867 mL·h−¹. Exogenous CHO oxidation from GEL and DRINK showed a similar time course,with peak exogenous CHO oxidation rates being reached at the end of the 180-min exercise. Peak exogenous CHO oxidation rates were not significantly different (P = 0.40) between GEL and DRINK (1.44 ± 0.29 vs 1.42 ± 0.23 g·min−¹, respectively). Furthermore, oxidation efficiency was not significantly different (P = 0.36) between GEL and DRINK (71% ± 15% vs 69% ± 13%, respectively). This study demonstrates that a GLU + FRC mixture is oxidized to the same degree then administered as either semisolid GEL or liquid DRINK, leading to similarly high peak oxidation rates and oxidation efficiencies.

Preparation of ZnO thin film by the sol-gel method using low temperature ozone oxidation

Zinc oxide thin films have been prepared by the sol–gel method from a 2-methoxyethanol solution of zinc acetate dihydrate on SiO2 substrates using air, pure oxygen, and 1% ozone in oxygen as oxygen source. In the cases where air or oxygen was used as the oxygen source for thermal annealing, samples annealed at 600 to 800 °C exhibit a (0002) peak in X-ray diffraction (XRD). A sample annealed at 700 °C exhibited the highest (0002) peak intensity in conventional thermal annealing. However, the case using 1% ozone in oxygen as the atmosphere presented different results. A sample treated in 1% ozone at 100 °C had peak intensity in XRD (0002) comparable with samples annealed at several hundreds of degree in air or oxygen. This result indicates that the high oxidation efficiency of ozone is useful in decreasing the processing temperature of the sol–gel method.

Diuron abatement using activated persulphate: Effect of pH, Fe(II) and oxidant dosage

The high oxidation efficiencies of the free radicals (SO 4 −), in combination with the slow rate of consumption of the oxidant, make this process very effective for the degradation of organic herbicides. Effects of pH, persulphate and Fe(II) concentration on the destruction of diuron by heat-assisted persulphate were examined in batch experiments. All the experiments were performed at 50 °C and an initial diuron concentration of 0.09 mM. The effectiveness of the process was evaluated based on the degradation of diuron and total organic carbon (TOC) removal. Under the reaction conditions, the diuron conversion is enormously influenced by the presence of Fe(II) in solution which rapidly produces the sulphate radical. Fe(II) concentration significantly accelerates diuron degradation at the first stages where the Fe(II) is oxidized to ferric iron. Increasing the persulphate concentration from 1 to 2.1 mM at natural pH accelerated the oxidation rate of diuron, which achieved 60% oxidation in 180 and 90 min, respectively. For the higher persulphate concentration (2.1 mM), complete diuron oxidation was achieved at 0.72 mM Fe(II) concentration in a few minutes. Additionally, diuron degradation by persulphate in bicarbonate-buffer solution was slower, most likely due to the presence of bicarbonate ions (radical scavengers).

High efficient electrocatalytic oxidation of methanol on Pt/polyindoles composite catalysts

Novel composite catalysts have been fabricated by the electrodeposition of Pt onto the glassy carbon electrode (GC) modified respectively with polyindole (PIn) and poly(5-methoxyindole) (PMI) and used for the electrooxidation of methanol in acid solution of 0.5 M H 2SO 4 containing 1.0 M methanol. As-formed composite catalysts are characterized by SEM, XRD and the electrochemical methods. The results of the catalytic activity for methanol oxidation show that the two composite catalysts exhibit higher catalytic activity and stronger poisoning-tolerance than Pt/polypyrrole/GC (Pt/PPy/GC) and Pt/GC. Electrochemical impedance spectroscopy indicates that the methanol electrooxidation on the composite catalysts at various potentials shows different impedance behaviors. At the same time, the charge-transfer resistance for electrooxidation of methanol on Pt/PIn/GC and Pt/PMI/GC is smaller than those on Pt/PPy/GC and Pt/GC. The present study shows a promising choice of Pt/PIn and Pt/PMI as composite catalysts for methanol electrooxidation.

High efficient electrocatalytic oxidation of formic acid on Pt/polyindoles composite catalysts

Four novel composite catalysts have been developed by the electrodeposition of Pt onto glassy carbon electrode (GCE) modified with polyindoles: polyindole, poly(5-methoxyindole), poly(5-nitroindole) and poly(5-cyanoindole). As-formed composite catalysts are characterized by SEM, XRD and electrochemical analysis. Compared with Pt nanoparticles, respectively, deposited on the bare GCE and on the GCE modified with polypyrrole, the four newly developed composite catalysts exhibit higher catalytic activity towards formic acid electrooxidation by improving selectivity of the reaction via dehydrogenation pathway and thus mostly suppressing the generation of poisonous CO ads species. The enhanced performance is proposed to come from the synergetic effect between Pt and polyindoles and the increase of electrochemical active surface area (EASA) of Pt on polyindoles.

Synergistic effect of vanadium–phosphorus promoted oxidation of benzylic alcohols with molecular oxygen in water

The synergistic effect of vanadium–phosphorus in aqueous solution is crucial to ensure high efficiency for oxidation of benzylic alcohols with molecular oxygen in water catalyzed by VOPO4/TEMPO (2,2,6,6-tetramethylpiperidyl-1-oxy).

F211 高圧筒内直接噴射式水素エンジンの噴流形成が熱効率およびNOx排出量に及ぼす影響に関する研究(OS3 バイオマス・新燃料・環境技術)

In hydrogen engine, high thermal efficiency and low nitrogen oxide (NOx) emissions are required. For the achievement of them, there are many possible combinations of injection pressure, injection timing and ignition timing that can be used in a system that injects the fuel directly into the cylinder. In this study, different combinations of injection and ignition timings were classified as three combustion regimes, and experiments were conducted to make clear that each combustion regimes has their optimized fuel spray design for high thermal efficiency and low NOx emissions..

Sulfate radical-based ferrous–peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems

Polychlorinated biphenyls (PCBs) in the environment pose long-term risk to public health because of their persistent and toxic nature. This study investigates the degradation of PCBs using sulfate radical-based advanced oxidation processes (SR-AOPs). These processes are based on the generation of sulfate radicals through iron (Fe(II), Fe(III)) mediated activation of peroxymonosulfate (KHSO5, PMS) or persulfate (Na2S2O8, PS). This study is the first instance for coupling of Fe(II)/Fe(III) with PMS for PCB degradation in aqueous and sediment systems. The high oxidation efficiencies of the free radicals (SO4−), in combination with the slow rate of consumption of the oxidants, make these processes very effective for the degradation of recalcitrant organic compounds. The effectiveness of the process was evaluated based on the degradation of a model polychlorinated biphenyl, 2-chlorobiphenyl and total organic carbon (TOC) removal. The kinetics of 2-chlorobiphenyl degradation along with the effect of oxidant and catalyst concentrations on the degradation efficiency was studied. Near complete removal of 2-chlorobiphenyl was observed when Fe(II) was used with PMS or PS. Fe(II) acts as a sulfate radical scavenger at higher concentrations indicating that there is an optimum concentration of Fe(II) that leads to most effective degradation of the target contaminant. A chelating agent, sodium citrate, was used to control the quantity of iron in the solution for activation of the oxidant. For the first time, we studied the feasibility of the activation of PMS using iron citrate complexes for PCB degradation. In the presence of sodium citrate, increase in degradation efficiency was observed up to a metal:ligand ratio of 1:2, after which the increase in citrate concentration led to a decrease in removal efficiency. Fe(II)/PMS systems were found to be very effective in degrading PCB in a sediment-slurry system with more than 90% PCB removal being observed within 24h.

Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate

Municipal landfill leachate, especially mature leachate, may disrupt the performance of moderately-sized municipal activated sludge wastewater treatment plants, and likewise tend to be recalcitrant to biological pretreatment. Recently, Fenton methods have been investigated for chemical treatment or pre-treatment of mature leachate. In this paper, the results of laboratory tests to determine the roles of oxidation and coagulation in reducing the organic content of mature leachate during Fenton treatment are presented. The efficiencies of chemical oxygen demand (COD) oxidation and coagulation were tested, and the ratio of COD removal by oxidation to that by coagulation was assessed, under various operating conditions. Low initial pH, appropriate relative and absolute Fenton reagent dosages, aeration, and stepwise addition of reagents increased COD removal by oxidation and the importance of oxidation relative to coagulation. Simultaneous aeration and stepwise reagent addition allowed comparable treatment without initial acidification pH, due to the generation of acidic organic intermediates and the continuous input of CO 2. On the other hand, high COD oxidation efficiency and low ferrous dosage inhibited COD removal by coagulation. At significantly high oxidation efficiency, overall COD reduction decrease slightly due to low coagulation efficiency. Under the most favorable conditions (initial pH 3, molar ratio [H 2O 2]/[Fe 2+] = 3, [H 2O 2] = 240 mM, and six dosing steps), 61% of the initial COD was removed, and the ratio of COD removal oxidation to coagulation was 0.75. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of mature leachate, and the role of oxidation in controlling the efficiency of removal of COD by coagulation.

Nanostructured Platinum/Iron Phosphate Thin-Film Electrodes for Methanol Oxidation

Nanostructured Pt-FePO 4 thin-film electrodes consisting of Pt nanocrystals and amorphous FePO 4 were fabricated by cosputtering, and nanocomposites containing ∼3 or ∼5 nm Pt crystalline phases were obtained. Compared with the pure Pt electrodes, the Pt-FePO 4 electrodes containing ∼3 nm Pt nanophases showed a significantly high efficiency, stability, and low charge-transfer resistance for methanol oxidation. The improved catalytic activities of the Pt-FePO 4 thin-film electrodes can be attributed to both an increase in the active surface area, and the possible ability of FePO 4 for the effective transfer of protons and the CO oxidation during methanol oxidation.

Catalytic Oxidation of Mixed Wastes Containing High Organic Content—Emission Reduction and the Effect of Steam

To resolve mixed organic and radioactive waste disposal problems, Lawrence Berkeley National Laboratory (LBNL) initiated a treatability study using the catalytic chemical oxidation (CCO) system to oxidize a mixed-waste stream and to confine tritium as part of LBNL's pollution prevention program. LBNL has also adopted a legal approach by seeking an equivalent waste-treatment determination for the CCO process, and by petitioning the United States Environmental Protection Agency (EPA) to delist F-coded treatment residues. The results of this study demonstrate that (1) the CCO process can treat aqueous wastes containing a broad range of organic chemicals and achieve more than 99.999% destruction efficiency; (2) greater than 99.9% trapping efficiency for tritiated water can be achieved using an emission-reduction system that also confines the vapor of hydrochloric acid or nitric acid to the liquid residue; and (3) neutralized treatment residues can be disposed of as low-level radioactive waste at a permitted facility after EPA has approved LBNL's petitions, or the tritium in the residues can be recycled. The high oxidation efficiency of the CCO process is mainly due to the optimized operating conditions of the CCO process and the combined effect of steam reforming in the oxidation cell and the catalytic oxidation of organic mixtures and CO in the Pt/Al2O3 catalyst bed.

The membrane application on the wastewater reclamation and reuse from the effluent of industrial WWTP in northern Taiwan

This is the first full scope study of wastewater reclamation and reuse on public WWTP in Taiwan. A 50 m 3/day pilot plant with membrane and biological systems of wastewater reclamation has been deployed and operated in the WWTP of Hsinchu Industrial Park, northern Taiwan. The reclaimed water has been transported to five factories and been used as the fresh water supply as well as the makeup water of cooling tower. The future construction of a 10,000 m 3/day wastewater reclamation plant has been proposed and financially investigated. The business plan of BTO is proposed for future development. The 50 m 3/day pilot plant consists of a membrane UF/RO system followed by the systems of high efficient biological oxidation systems BioNET and/or BAC. The bench-scale membrane scaling/fouling test and magnetic anti-scaling system are also introduced to verify the mechanisms of membrane scaling and fouling. The result of the pilot study shows that the reclaimed water can conform the drinking water standard and can be used as the make-up water of cooling tower as well as the manufacturing water of many industrial applications. The concentrate of RO process can fit the effluent standard and can be discharged directly to the river nearby. There are 88.6% of the factories in the industrial park express their willingness of using reclaimed water and 4600 m 3/day is requested after the preliminary poll. The cost of reclaimed water is around US$0.54/m 3 (including construction, O & M and transportation) which is higher than the tariff of tap water (US$0.27/m 3) but lower than the cost of seawater desalination as well as that of reservoir construction. Under BTO business plan, a wastewater reclamation plant of minimum 10,000 m 3/day is proposed in order to make profit for future operation.

Effect of Oxygen on the Formation and Decay of Stilbene Radical Cation during the Resonant Two-Photon Ionization

Formation and decay of radical cations of trans-stilbene and p-substituted trans-stilbenes (S.+) during the resonant two-photon ionization (TPI) of S in acetonitrile in the presence and absence of O(2) have been studied with laser flash photolysis using a XeCl excimer laser (308 nm, fwhm 25 ns). The transient absorption spectra of S.+ were observed with a peak around 470-490 nm. The formation quantum yield of S.+ (0.06-0.29) increased with decreasing oxidation potential (E(ox)) and increasing fluorescence lifetime (tau(f)) of S, except for trans-4-methoxystilbene which has the lowest E(ox) and longer tau(f) among S. The considerable low yield and fast decay in a few tens of nanoseconds time scale were observed for trans-4-methoxystilbene.+ in the presence of O(2), but not for other S.+ . It is suggested that formation of the ground-state complex between trans-4-methoxystilbene and O(2) and the distonic character of trans-4-methoxystilbene.+ with separation and localization of the positive charge on the oxygen of the p-methoxyl group and an unpaired electron on the beta-olefinic carbon are responsible for the fast reaction of trans-4-methoxystilbene.+ with O(2) or superoxide anion, leading to the considerable low yield and fast decay of trans-4-methoxystilbene.+ . The mechanism based on the transient absorption measurement of S.+ during the TPI is consistent with the relatively high oxidation efficiency of trans-4-methoxystilbene among S based on the product analysis during the photoinduced electron transfer in the presence of a photosensitizer such as 9,10-dicyanoanthracene and O(2) in acetonitrile.

Development of a Gravity‐Independent Wastewater Bioprocessor for Advanced Life Support in Space

Operation of aerobic biological reactors in space is controlled by a number of challenging constraints, mainly stemming from mass transfer limitations and phase separation. Immobilized-cell packed-bed bioreactors, specially designed to function in the absence of gravity, offer a viable solution for the treatment of gray water generated in space stations and spacecrafts. A novel gravity-independent wastewater biological processor, capable of carbon oxidation and nitrification of high-strength aqueous waste streams, is presented. The system, consisting of a fully saturated pressurized packed bed and a membrane oxygenation module attached to an external recirculation loop, operated continuously for over one year. The system attained high carbon oxidation efficiencies often exceeding 90% and ammonia oxidation reaching approximately 60%. The oxygen supply module relies on hydrophobic, nonporous, oxygen selective membranes, in a shell and tube configuration, for transferring oxygen to the packed bed, while keeping the gaseous and liquid phases separated. This reactor configuration and operating mode render the system gravity-independent and suitable for space applications.

Meso- and macro-porous Pd/CexZr1–xO2 as novel oxidation catalysts

A new class of high-efficiency oxidation catalysts has been prepared using a combined surfactant and colloidal crystal templating method. The Pd/CexZr1−xO2 products possess mesoporous structures and macrochannels. XRD and EXD analyses confirmed the formation of a 0.8 wt.% Pd/Ce0.6Zr0.4O2 with a cubic phase at temperatures above 700 °C. With increasing calcination temperature, better crystallization of the cubic phase and incorporation of more zirconium into the ceria lattice were observed. The extent of surface Ce3+ and oxygen vacancies on the samples were studied by the XPS measurements. The T50 and T90 for CO oxidation over Pd supported catalysts were 65 °C and 75 °C respectively. These values were better than those obtained from catalysts without macrochannel structures and the one prepared by the co-precipitation method. Such high catalytic efficiency can be explained by the high crystal phase homogeneity, availability of more oxygen vacancies and an enlarged surface area.