Pt/Mg-Ce-O catalyst for NO/H<Subscript>2</Subscript>/O<Subscript>2</Subscript> lean de-No<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> reaction

The NO/H₂/O₂ reaction was studied under oxidizing conditions in the 100-400 °C range over 0.1 wt% Pt supported on various metal oxides such as MgO, CeO₂, SiO₂, La₂O₃, CaO, Y₂O₃ and TiO₂. The Pt/MgO and Pt/CeO₂ catalysts showed good catalytic behaviours. Here, we find that the Pt/Mg-Ce-O catalyst, prepared from MgO and CeO₂ by the sol-gel method, is a very active and selective catalyst towards N₂ formation in the whole 100–400 °C range. This catalyst appears to be the most active, selective and stable one ever reported in the literature for the NO/H₂/O₂ reaction, even in the presence of 5%v H₂O or 20 ppmv of SO₂ in the feed stream.Selected article from the Regional Symposium on Chemistry and Environment, Krusevac, Serbia, June 2003, organised by Dr. Branimir Jovancicevic.     

Metal-free oxidation of aldehydes to acids using the 4Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O<Subscript>2</Subscript>·NaCl adduct

Oxidation of aldehydes to carboxylic acids is a major reaction. Conventionally, this reaction is carried out with oxidants and metal catalysts, thus producing unwanted metal waste. Recently, aqueous media have been used as an alternative for toxic organic solvents. Here, we tested the clathrate-structured, neutral hydrogen peroxide adduct 4Na₂SO₄·2H₂O₂·NaCl for the oxidation of aldehydes to acids in aqueous solution. We found that various aromatic, heteroaromatic and aliphatic aldehydes were selectively oxidized to corresponding acids in 70–98% yields. This simple acid–base treatment allows to separate easily the acid product in high purity without any organic solvent. Moreover, the adduct is produced using 25% H₂O₂, with inexpensive sodium sulphate, Na₂SO₄, and sodium chloride, NaCl. The adduct is a non-toxic white crystalline solid, readily soluble in water, and easy to handle.     

Interaction between cadmium,lead and potassium fertilizer (K<Subscript>2</Subscript>SO<Subscript>4</Subscript>) in a soil-plant system

A pot experiment was conducted to examine the influence of potassium (K) fertilizer (K₂SO₄) application on the phytoavailability and speciation distribution of cadmium (Cd) and lead (Pb) in soil. Spring wheat (Triticum aestivum L.) was selected as the test plant. There were seven treatments including single and combined contamination of Cd and Pb. CdCl₂·2.5 H₂O and Pb(NO₃)₂ were added to the soil at the following dosages: Cd + Pb = 0.00 + 0.00, 5.00 + 0.00, 25.0 + 0.00, 0.00 + 500, 0.00 + 1000, 5.00 + 500 and 25.0 + 1000 mg kg⁻¹, denoted by CK, T1, T2, T3, T4, T5 and T6, respectively. The K fertilizer had five levels: 0.00, 50.0, 100, 200 and 400 mg K₂O kg⁻¹ soil, denoted by K0, K1, K2, K3 and K4, respectively. The results showed that the K fertilizer promoted the dry weight (DW) of wheat in all treatments and alleviated the contamination by Cd and Pb. The application of K₂SO₄ reduced the uptake of Cd in different parts including roots, haulms and grains of wheat; the optimum dosage was the K2 level. K supply resulted in a significant (P < 0.05) decrease in the soluble plus exchangeable (SE) fraction of Cd and there was a negative correlation (not significant, P > 0.05) between the levels of K and the SE fraction of Cd in soil. The application of the K fertilizer could obviously restrain the uptake of Pb by wheat and there were significant (P < 0.05) negative correlations between the concentrations of Pb in grains and the levels of K in soil. K supply resulted in a decrease in the SE fraction of Pb (except the K1 level) from the K0 to K4 levels. At the same time, the application of the K fertilizer induced a significant (P < 0.05) decrease in the weakly specifically adsorbed (WSA) fraction of Pb and a significant (P < 0.05) increase in the bound to Fe–Mn oxides (OX) fraction of Pb. At different K levels, the concentration of Pb in the roots, haulms and grains had a positive correlation with the SE (not significant, P > 0.05) and WSA (significant, P < 0.05) fractions of Pb in the soil. All the K application levels in this experiment reduced the phytoavailability of Cd and Pb. Thus, it is feasible to apply K fertilizer (K₂SO₄) to alleviate contamination by Cd and/or Pb in soil. Moreover, the level of K application should be considered to obtain an optimal effect with the minimum dosage.     

Degradation of carbendazim by UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> investigated by kinetic modelling

The transformation of the fungicide carbendazim (methyl-2 benzimidazole carbamate) induced by hydroxyl radical generated by the UV photolysis of H₂O₂ has been studied in dilute aqueous solution. The efficient reaction of hydroxyl radicals with carbendazim led to the rapid degradation of carbendazim. The study of reaction kinetics yielded a second order rate constant of 2.2±0.3 10⁹ M⁻¹ s⁻¹ for HO^· radicals with carbendazim. This value is in agreement with a high reactivity of HO^· radicals with carbendazim. Most degradation products were identified by high performance liquid chromatography mass spectrometry (HPLC-MS). In the presence of hydrogenocarbonate and carbonate ions, hydroxyl radicals were quenched and in turn carbonate radicals CO₃ ^·− were formed. Carbonate radicals are indeed known to react efficiently with compounds containing electron-rich sites such as nitrogen or sulfur atoms. The use of a kinetic modelling software gave evidence for the occurrence of such reactions with carbendazim. The second order rate constant of carbonate radical with carbendazim was equal to 6±2 10⁶ M⁻¹ s⁻¹. Electronic Publication     

Photocatalytic degradation of the herbicide cinosulfuron in aqueous TiO<Subscript>2</Subscript> suspension

The photocatalytic degradation of a sulfonylurea herbicide, cinosulfuron, has been studied in TiO₂ aqueous suspensions. A first order kinetic law was found. The influence of the initial concentration of cinosulfuron and of the initial radiant flux on the kinetics were evaluated. The identification of the intermediate products was based on high performance liquid chromatography coupled with mass spectrometry analyses (HPLC-MS). The mineralization of cinosulfuron was traced using ion chromatography and total organic carbon (TOC) measurements. These results indicate that the photocatalytic degradation of cinosulfuron leads to CO₂, NO₃ ⁻ and SO₄ ²⁻ as final products, and in addition cyanuric acid (C₃H₃O₃N₃), confirming previous results on triazinic ring-containing compounds. Electronic Publication     

Static and dynamic characteristics of SO<Subscript>2</Subscript>-O<Subscript>2</Subscript> aqueous solution in the microstructure of porous carbon materials

Porous carbon material facilitates the reaction SO₂ + O₂ + H₂O → H₂SO₄ in coal-burned flue gas for sulfur resources recovery at mild conditions. It draws a long-term mystery on its heterogeneous catalysis due to the complicated synergic effect between its microstructure and chemical components. To decouple the effects of geometric structure from chemical components, classical molecular dynamics method was used to investigate the static and dynamic characteristics of the reactants (H₂O, SO₂ and O₂) in the confined space truncated by double-layer graphene (DLG). Strong adsorption of SO₂ and O₂ by the DLG was observed, which results in the filling of the solute molecules into the interior of the DLG and the depletion of H₂O. This effect mainly results from the different affinity of the DLG to the species and can be tuned by the separation of the two graphene layers. Such dimension dependence of the static and dynamic properties like distribution profile, molecular cluster, hydrogen bond and diffusion coefficient were also studied. The conclusions drawn in this work could be helpful to the further understanding of the underlying reaction mechanism of desulfurization process in porous carbon materials and other applications of carbon-based catalysts.

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Hydrogen peroxide (H2O2) requirement for the oxidation of crude oil in contaminated soils by a modified Fenton's reagent

The oxidation of soil organic matter (SOM) and total petroleum hydrocarbon were investigated in two soils at eight different hydrogen peroxide (H₂O₂) concentrations to determine the optimal H₂O₂ dosage for the efficient remediation of soils contaminated by crude oil with minimal SOM removal. In our study, H₂O₂ concentrations up to 1100 mM increased the SOM destruction up to 10%–15% in the two soils while no improvement of the crude oil removal efficiencies was observed. The results indicate that the destruction of SOM significantly limits the oxidation of crude oil because SOM might consume H₂O₂ more effectively than crude oil at H₂O₂ concentrations above 1100 mM. In addition, H₂O₂ concentrations higher than 1100 mM were not expected for both soils because of the extremely rapid H₂O₂ decomposition, and low H₂O₂ utilization, of both soils.     

Gas-phase degradation of CCl<Subscript>4</Subscript>, CHCl<Subscript>3</Subscript> and CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript> over metallic Fe

We studied the hydrolysis of gas-phase carbon tetrachloride (CCl₄), chloroform (CHCl₃), and dichloromethane (CH₂Cl₂) over a metallic Fe surface for its application in combination with air stripping and soil vapour extraction. The effects of chlorocarbon concentration, type and preparation of the iron-containing material, humidity, and temperature on process performance are reported. The hydrolysis of chlorinated methane derivatives is catalysed by metallic iron resulting in a noticeable decrease of the reaction temperature. The reaction kinetics were found to be consistent with the Langmuir-Hinshelwood model.     

Effects of Pd doping on N<Subscript>2</Subscript>O formation over Pt/BaO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> during NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> storage and reduction process

N₂O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N₂O formation over Pt/BaO/Al₂O₃ catalyst. Three types of catalysts, Pt/BaO/Al₂O₃, Pt/Pd mechanical mixing catalyst (Pt/BaO/Al₂O₃ + Pd/Al₂O₃) and Pt-Pd co-impregnation catalyst (Pt-Pd/BaO/Al₂O₃) were prepared by incipient wetness impregnation method. These catalysts were first evaluated in NSR activity tests using H₂/CO as reductants and then carefully characterized by BET, CO chemisorption, CO-DRIFTs and H2-TPR techniques. In addition, temperature programmed reactions of NO with H2/CO were conducted to obtain further information about N₂O formation mechanism. Compared with Pt/BaO/Al₂O₃, (Pt/BaO/ Al₂O₃ + Pd/Al₂O₃) produced less N₂O and more NH3 during NO _x storage and reduction process, while an opposite trend was found over (Pt-Pd/BaO/Al₂O₃ + Al₂O₃). Temperature programmed reactions of NO with H₂/CO results showed that Pd/Al₂O₃ component in (Pt/BaO/Al₂O₃ + Pd/Al₂O₃) played an important role in NO reduction to NH₃, and the formed NH3 could reduce NO _x to N₂ leading to a decrease in N₂O formation. Most of N₂O formed over (Pt-Pd/BaO/Al₂O₃ + Al₂O₃) was originated from Pd/BaO/Al₂O₃ component. H₂-TPR results indicated Pd-Ba interaction resulted in more difficultto- reduce PdOx species over Pd/BaO/Al₂O₃, which inhibits the NO dissociation and thus drives the selectivity to N₂O in NO reduction.

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Preparation of effective TiO<Subscript>2</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> photocatalysts for water treatment

Photocatalytic oxidation using semiconductors is one of the advanced oxidation processes for degradation of organic pollutants in water and air. TiO₂ is an excellent photocatalyst that can mineralize a large range of organic pollutants such as pesticides and dyes. The main challenge is to improve the efficiency of the TiO₂ photocatalyst and to extend TiO₂ light absorption spectra to the visible region. A potential solution is to couple TiO₂ with a narrow band gap semiconductor possessing a higher conduction band such as bismuth oxide. Therefore, here we prepared Bi₂O₃/TiO₂ heterojunctions by the impregnation method with different Bi/Ti ratio. The prepared composites have been characterized by UV–Vis diffused reflectance spectra and X-ray diffraction. The photocatalytic activity of the heterojunction has been determined from the degradation of orange II under visible and UV light. Results show that Bi₂O₃/TiO₂ heterojunctions are more effective than pure TiO₂-anatase under UV-A irradiation, with an optimum for the Bi/Ti ratio of 5 %, for the photocatalytic degradation of Orange II. However, the photocatalytic activity under irradiation at λ higher than 420 nm is not much improved. Under UV–visible radiation, the two semiconductors are activated. We propose a mechanism explaining why our products are more effective under UV–visible irradiation. In this case the charge separation is enhanced because a part of photogenerated electrons from the conduction band of TiO₂ will go to the conduction band of bismuth oxide. In this composite, titanium dioxide is the main photocatalyst, while bismuth oxide acts as adsorbent photosensitizer under visible light.     

五氧化二钒类Fenton降解邻苯二甲酸二乙酯的机制研究

发展了基于五氧化二钒(V_2O_5)和过氧化氢(H_2O_2)的新型类Fenton体系,探索了此体系产生羟基(·OH)的机制及降解邻苯二甲酸二乙酯(DEP)的效率;并考察了V_2O_5投加量、H_2O_2浓度,以及草酸对DEP降解的影响。结果表明,当V_2O_5投加量为0.1 g·L-1,H_2O_2浓度为2.0 mmol·L-1,反应24 h后,对DEP(25 mg·L-1)的降解率可达61.1%,增加或降低V_2O_5投加量和H_2O_2浓度均不利于DEP的降解。利用电子顺磁共振技术(Electron Paramagnetic Resonance,EPR)耦合5,5-二甲基-1-吡咯啉氮氧化物(DMPO)为捕获剂对反应体系中的主导自由基进行鉴定,发现·OH是体系降解DEP的主要活性物种,利用苯甲酸作为探针分子实现了·OH的间接定量,并初步推测了V_2O_5活化H_2O_2的过程。     

Investigation of the effects of humic acid and H<Subscript>2</Subscript>O<Subscript>2</Subscript> on the photocatalytic degradation of atrazine assisted by microwave

A solution of atrazine in a TiO₂ suspension, an endocrine disruptor in natural water, was tentatively treated by microwave-assisted photocatalytic technique. The effects of mannitol, oxygen, humic acid, and hydrogen dioxide on the photodegradation rate were explored. The results could be deduced as follows: the photocatalytic degradation of atrazine fits the pseudo-first-order kinetic well with k = 0.0328 s^?1, and ·OH was identified as the dominant reactant. Photodegradation of atrazine was hindered in the presence of humic acid, and the retardation effect increased as the concentration of humic acid increased. H₂O₂ displayed a significant negative influence on atrazine photocatalysis efficiency. Based on intermediates identified with gas chromatography-mass spectrometry (GC-MS) and Liquid chromatography-mass spectrometry (LC-MS/MS) techniques, the main degradation routes of atrazine are proposed.     

Covering α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> protection layer on the surface of p-Si micropillar array for enhanced photoelectrochemical performance

The spontaneous oxidation process of pristine silicon (Si) limits its application as photocatalyst or electrode in aqueous solution or moist air. Covering a protection layer on Si surface is an effective approach to overcome this disadvantage. In this paper, α-Fe₂O₃ is demonstrated to be an excellent alternative as a protection material. α-Fe₂O₃ layer was deposited around each p-type Si micropillar (SiMP) in well-ordered array by chemical bath deposition method. The diameter of SiMP was 5 mm and the thickness of α-Fe₂O₃ layer was about 20 nm. The photoeletrochemical stability of SiMP/α-Fe₂O₃ was proved by 10 circles cyclic voltammetry testing. Compared with SiMP, its optical absorption and photocurrent density improved 2 times and 4 times, respectively, and its onset potential for hydrogen evolution moved positively about 0.4 V. These improved performances could be ascribed to the enhanced photogenerated-charge-separation efficiency deriving from built-in electric field at the interface between Si and α-Fe₂O₃. The above results show an effective strategy to utilize Si material as photocatalyst or electrode in aqueous solution or moist air.

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Sonocatalytic degradation of tetracycline antibiotic in aqueous solution by sonocatalysis

Tetracycline (TC), one of the most common antibiotics, is often poorly bio-degraded in conventional wastewater treatment plants. In this study, the sonocatalytic degradation of TC was investigated using TiO₂ nano-particles as catalyst. The effect of pH, initial TC concentrations, reaction times, and H₂O₂ concentrations were evaluated. The efficacy of ultrasonic irradiation alone in the removal of this pollutant was negligible but removal efficiency increased upon addition of TiO₂ up to 250 mg L^?1; increase of pH and initial TC concentration attenuated TC degradation. Addition of H₂O₂ raised the removal efficiency so that complete removal of TC was achieved within 75 min.     

Photocatalytic formation of hydrogen peroxide over highly porous illuminated ZnO and TiO2thin film

The photocatalytic formation of hydrogen peroxide over ZnO and TiO₂thin films has been investigated in aqueous phase in the presence of molecular oxygen as an electron acceptor. These films are highly porous and showed enhanced catalytic activity in the photochemical formation of hydrogen peroxide. The amount of H₂O₂formed during 2 hour light illumination is 4–6 μM and the rates of formation of hydrogen peroxide of both the films are almost comparable. The yield of hydrogen peroxide increases with the increase in irradiation time and a trend of steady state concentration of H₂O₂is observed in the case of TiO₂thin film. Photodissolution of ZnO particles is observed in some extent during the process of prolonged UV light illumination.     

Physiological adaptations of the invasive cordgrass<Emphasis Type="Italic"> Spartina anglica</Emphasis> to reducing sediments: rhizome metabolic gas fluxes and enhanced O<Subscript>2</Subscript> and H<Subscript>2</Subscript>S transport

Cordgrasses of the genus Spartina form dense monospecific stands worldwide, profoundly influencing the ecology of estuaries. One species, Spartina anglica, originated by allopolyploidy in the 1800s and has been particularly prolific as an invasive species worldwide. S. anglica tolerates low-lying estuarine mudflats that its progenitor species and other coastal halophytes cannot. However, very little is known of the physiology of S. anglica. In the present study, an automated flow-through respirometry system was used to quantify metabolic gas fluxes (O₂, H₂S, CO₂, and NH₃) of S. anglica rhizomes. Enhanced physiological mechanisms to transport O₂ and H₂S in both directions between the rhizosphere and the atmosphere were exhibited by S. anglica, but not by the native North American species S. alterniflora. These results suggest that tolerance of anoxia and H₂S may assist S. anglica in colonizing extensively flooded environments. Enhanced sediment oxygenation by S. anglica may be potentially useful for phytoremediation of contaminated sediments, since microbial degradation of organic pollutants is often limited by O₂ availability.     

Promotion of transition metal oxides on the NH<Subscript>3</Subscript>-SCR performance of ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> catalyst

Chromium oxide and manganese oxide promoted ZrO₂-CeO₂ catalysts were prepared by a homogeneous precipitation method for the selective catalytic reduction of NO _x with NH₃. A series of characterization including X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), Brunauer–Emmett–Teller (BET) surface area analysis, H₂ temperatureprogrammed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the influence of the physicochemical properties on NH₃-SCR activity. Cr-Zr-Ce and Mn-Zr-Ce catalysts are much more active than ZrO₂-CeO₂ binary oxide for the low temperature NH₃-SCR, mainly because of the high specific surface area, more surface oxygen species, improved reducibility derived from synergistic effect among different elements. Mn-Zr-Ce catalyst exhibited high tolerance to SO₂ and H₂O. Cr-Zr-Ce mixed oxide exhibited>80% NO _x conversion at a wide temperature window of 100°C–300°C. In situ DRIFT studies showed that the addition of Cr is beneficial to the formation of Bronsted acid sites and prevents the formation of stable nitrate species because of the presence of Cr^{6 +}. The present mixed oxide can be a candidate for the low temperature abatement of NO _x .

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Enhanced heterogeneous Fenton-like activity by Cu-doped BiFeO<Subscript>3</Subscript> perovskite for degradation of organic pollutants

Heterogeneous Fenton-like reaction has been extensively investigated to eliminate refractory organic contaminants in wastewater, but it usually shows low catalytic performance due to difficulty in reduction from Fe(III) to Fe(II). In this study, enhanced catalytic efficiency was obtained by employing Cu-doped BiFeO₃ as heterogeneous Fenton-like catalysts, which exhibited higher catalytic performance toward the activation of H₂O₂ for phenol degradation than un-doped BiFeO₃. BiFe_0.8Cu_0.2O₃ displayed the best performance, which yielded 91% removal of phenol (10 mg L^–1) in 120 min. The pseudo first-order kinetic rate constant of phenol degradation in BiFe_0.8Cu_0.2O₃ catalyzed heterogeneous Fenton-like reaction was 5 times higher than those of traditional heterogeneous Fenton-like catalysts, such as Fe₃O₄ and goethite. The phenol degradation efficiency could still reach 83% after 4 cycles, which implied the good stability of BiFe_0.8Cu_0.2O₃. The high catalytic activity of BiFe_0.8Cu_0.2O₃ was attributed to the fact that the doping Cu into BiFeO₃ could promote the generation of Fe(II) in the catalyst and then facilitate the activation of H₂O₂ to degrade the organic pollutants.

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Reductive dechlorination of chlorobenzene in supercritical water catalyzed by Fe/ZrO<Subscript>2</Subscript>

Reductive dechlorination of chlorobenzene by Fe/ZrO₂ in supercritical water was investigated. The effects of the operation conditions were studied. The dechlorination of chlorobenzene obeyed pseudo-first-order kinetics models. In supercritical water, the rate constant increases more rapidly with temperature than those in subcritical water. The results showed that the rate-determining step of dechlorination in subcritical water is diffusion; whereas the rate-determining of dechlorination in supercritical water is chemical reaction. The reaction mechanism in subcritical water might involve with an ionic mechanism; whereas the reaction mechanism in supercritical water might involve with a homolytic reaction.     

Photocatalytic degradation of chlorophenols using Ru(bpy) 3 2+ /S2O 8 2−

Advanced oxidation processes, such as photocatalysed oxidation, provide an important route for degradation of wastes. In this study, the lowest excited state (³MLCT) of Ru(bpy)₃²⁺ is used to break down chlorophenol pollutant molecules to harmless products. This has the advantage of using visible light and a short-lived catalytically active species. Photolysis of deaerated aqueous solutions of a variety of mono- and poly-substituted chlorophenols has been followed in the presence of Ru(bpy)₃²⁺/S₂O₈²⁻ with near visible light (λ > 350 nm) by UV/visible absorption spectroscopy, luminescence, potentiometry, NMR and HPLC techniques. Upon irradiation, a decrease is observed in the chlorophenol concentration, accompanied by the formation of Cl⁻, H⁺ and SO₄²⁻ ions as the main inorganic products. Benzoquinone, phenol, dihydroxybenzenes and chlorinated compounds were the dominant organic products. As the ruthenium(II) complex is regenerated in the reaction, the scheme corresponds to an overall catalytic process. The kinetics of the rapid chlorophenol photodechlorination has been studied, and are described quite well by pseudo-first order behaviour. Further studies on this were made by following Cl⁻ release with respect to the initial Ru(bpy)₃²⁺ and S₂O₈²⁻ concentrations. A comparison is presented of the photodechlorination reactivity of the mono and polychlorophenols studied at acidic and alkaline pH.