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Applied Catalysis B, Environmental (v.66, #1-2)

EDITORIAL BOARD (pp. co2).

FULL TITLE (pp. i).

Calendar of Forthcoming Events (pp. ii).

Contents Continued (pp. i).

Systematic investigation of supported transition metal oxide based formulations for the catalytic oxidative elimination of (chloro)-aromatics by F. Bertinchamps; C. Grégoire; E.M. Gaigneaux (pp. 1-9).

This paper reports, for the first time, a systematic investigation (screening) of the catalytic activity of 40 different formulations of transition metal oxides-based supported catalysts in the course of the total oxidation of benzene as a model molecule for dioxin. The catalysts consisted in 10 different transition metal oxides (CrO_x, MnO_x, VO_x, SnO_x, WO_x, NbO_x, TaO_x, MoO_x, ZrO_x and BiO_x) supported on 4 different supports (2 kinds of TiO₂, Al₂O₃ and SiO₂). A theoretical coverage of 0.75 monolayer of active phase was chosen to minimize the formation of crystallites. XPS and XRD characterizations demonstrated the better spreading as monolayer of the active phases at the surface of titania than of Al₂O₃ and SiO₂. The latter induces a poor dispersion of almost all the active phases as crystallites. The variation of spreading of the active phases on the different supports is governed by the difference in surface free energy and is fully explained by the “solid–solid wetting�? concept. For almost all active phases, the conversion of benzene progressively improves when the support is changed from SiO₂ to Al₂O₃ and, finally, titanias. The performances of the active phases exhibiting this behavior, are clearly dictated by their presence as well-dispersed monolayers at the surface of the support. The screening revealed CrO_x, VO_x and MnO_x as the most active phases. The first two exhibit their best activity when spread as monolayer at the surface of TiO₂ based supports (classical behavior). At the opposite, MnO_x works best when present in the form of Mn₃O₄ crystallites on the SiO₂ support.

Keywords: Catalytic oxidation; VOC combustion; PCDDs/PCDFs; Benzene; Chlorobenzene; Screening; XRD

This contribution reports, for the first time, a systematic investigation of the effect of the adding secondary phases on the activity of VO_x/TiO₂ based catalysts in the course of the total oxidation of benzene and chlorobenzene as model molecules for dioxins. The catalysts consisted in binary formulations VO_x-secondary phases (CrO_x, MnO_x, SnO_x, WO_x, NbO_x, TaO_x, MoO_x, ZrO_x or BiO_x). Three synthesis pathways differing by the order of synthesis of both phases were investigated (1-2, 2-1 and 1,2 both together). Catalysts synthesized in a unique step demonstrated the best activities for the oxidation of benzene. Moreover, WO_x and MoO_x phases induce a synergetic effect with VO_x. XPS demonstrated that this effect resides in the absence of mutual spreading between both phases preventing the VO_x covering by the secondary phases and promoting the stabilization of the links VO_x-TiO₂.The investigation of different ratios WO_x/VO_x and MoO_x/VO_x on the total oxidation of chlorobenzene was performed on binary formulations supported on classical TiO₂ or on sulfated TiO₂. For both supports and both binary formulations, the optimum ratio is equal to 1. This ratio is the highest that prevents the presence of crystallites of MoO_x or WO_x, which seems to be detrimental for the catalyst activity. Moreover, the resistance of the formulations in front of the chlorinated volatile organic compounds (Cl-VOCs) and the better activity of the formulations supported on sulfated TiO₂ were proven.The activation effects brought by WO_x, MoO_x and by sulfated TiO₂ are linked to the increase of the number of Brønsted acid sites as proven by FTIR with adsorbed pyridine. Moreover, the strong Lewis sites present on the sulfated TiO₂ promote the dispersion of the active and secondary phases. Furthermore, these investigations pointed out the importance of the presence of Brønsted sites for the adsorption of VOCs and Cl-VOCs aromatics.

Keywords: Catalytic oxidation; VOC combustion; PCDDs/PCDFs; Benzene; Chlorobenzene; VO; _x; /TiO; ₂

Water gas shift activity and kinetics of Pt/Re catalysts supported on ceria-zirconia oxides by Rakesh Radhakrishnan; R.R. Willigan; Z. Dardas; T.H. Vanderspurt (pp. 23-28).

UTRC has developed a stable, high activity water gas shift (WGS) catalysts for the removal of carbon monoxide from hydrogen containing reformate, generated from natural gas. Hydrogen streams that contain lower concentrations of carbon monoxide poison can extend the life of proton exchange membrane (PEM) fuel cell stacks. This study presents WGS reactivity and kinetics experiments performed comparing platinum and platinum/rhenium (T.H. Vanderspurt, F. Wijzen, X. Tang, M.P. Leffler, R.R. Willigan, C.A. Newman, R. Radhakrishnan, F. Feng, B.L. Laube, Z. Dardas, S.M. Opalka, Y. She, US Patent Application 0235526 A1 (2003)) supported on high surface area (∼200m²/g), nano-crystalline (∼4nm) large average pore size (∼5nm) ceria-zirconia under various reaction conditions. These represent gas compositions and temperatures that the catalysts see in fuel processing systems. It was found that rhenium enhanced the WGS activity of ceria-zirconia supported platinum catalysts and that rhenium carbonyl Re₂(CO)₁₀ was an optimal source for introducing rhenium to the platinum/ceria-zirconia catalysts. The optimal platinum to rhenium ratio for these catalysts was approximately 2:1 (Pt/Re) where the platinum loading was about 2wt.%. A simple kinetic model adequately represents the rhenium promotion effect sufficient to size the WGS reactors for a system. This model suggests that the enhancement in reaction rates was a function of a larger positive order dependency for H₂O concentration with lower inhibitory orders for CO₂ and H₂ concentrations for the platinum/rhenium catalyst compared to the platinum only catalyst.

Keywords: Water gas shift; Fuel cells; Fuel processing; Reaction kinetics; Ceria; Zirconia; Noble metal; Platinum; Rhenium

Catalytic steam reforming of ethanol over high surface area CeO₂: The role of CeO₂ as an internal pre-reforming catalyst by N. Laosiripojana; S. Assabumrungrat (pp. 29-39).

In the present work, it was found that high surface area ceria (CeO₂ (HSA)), synthesized by a surfactant-assisted approach, have useful ethanol steam reforming activity under solid oxide fuel cells (SOFCs) temperatures. The catalyst provides good reforming reactivity and high resistance toward carbon deposition compared to Ni/Al₂O₃ and conventional low surface area ceria (CeO₂ (LSA)). Although the hydrogen selectivity at steady state from the ethanol steam reforming over CeO₂ (HSA) was lower than Rh/Al₂O₃, the resistance toward carbon deposition of CeO₂ (HSA) was considerably higher.At temperature 900°C, the main products from the steam reforming of ethanol over CeO₂ (HSA) (with inlet C₂H₅OH/H₂O molar ratio of 1.0/3.0) were H₂ (with the selectivity of 67.5%), CH₄, CO, and CO₂. In contrast, the formations of C₂H₄ and C₂H₆ were also observed from the steam reforming of ethanol over Ni/Al₂O₃ and CeO₂ (LSA). The combination use of CeO₂ and Ni/Al₂O₃ was studied in an annular ceramic reactor by applying CeO₂ as an internal pre-reforming catalyst. The main purpose of CeO₂ is to convert all ethanol and other high hydrocarbon compounds (e.g. C₂H₄ and C₂H₆) forming CH₄, CO, CO₂, and H₂, while Ni/Al₂O₃ is applied to reform all CH₄ left from the pre-reforming section and maximize the yield of hydrogen production. After operated at 900°C for 100h, this combination pattern offers high hydrogen selectivity (87.0–91.4%) and good resistance toward carbon deposition. This successful development eliminates the requirement of expensive noble metal catalysts or the installation of an external pre-reformer in order to reform ethanol internally (IIR-SOFC).

Keywords: Ethanol; Hydrogen; Internal reforming; Ceria; Redox

Removal of NO₃⁻ from water by electrochemical reduction in different reactor configurations by L. Szpyrkowicz; S. Daniele; M. Radaelli; S. Specchia (pp. 40-50).

A series of cathode materials were investigated to establish their performance towards the electrochemical reduction of nitrate ions in unbuffered aqueous solutions. In particular, Ti/PdO–Co₃O₄ (for simplicity Ti/Pd–Co), nanostructured SS/Pd–Cu (Cu content: 15%, w/w), Ti/Pd–Co loaded with small amounts of electrodeposited Cu (Ti/Pd–Co–Cu) electrodes were prepared and studied by using both cyclic voltammetry and exhaustive electrolysis experiments. Cyclic voltammetry was mainly employed to establish the potentials at which the reduction of NO₃⁻ and of one of the intermediate reduction products (NO₂⁻) occurred at the different materials, and the effect of copper, employed as a promoter, for the nitrate ion reduction. With this respect a bulk copper working electrode was also investigated. Exhaustive electrolysis were performed under stagnant and stirred conditions in either a single-cell batch or membrane reactor, operating at a constant potential. For the latter reactor, a thick Nafion 117 membrane was used to separate the cathodic from the anodic compartment. The experiments showed that good results, in terms of nitrate removal, were obtained by using the membrane reactor equipped with the Ti/Pd–Co–Cu cathode operating at −0.9V versus SCE, where the nitrate content was lowered from 200 down to 50mg/L, which represents the upper limit for drinking water. The performance of the various electrodes in the presence of NaClO₄ as base electrolyte in both compartments of the reactor, or NaCl as base electrolyte in the anodic compartment only, was also investigated in order to simultaneously remove nitrate and ammonia. The latter, which is the main final product formed in the reduction process, diffused through the Nafion membrane into the anodic compartment where it was oxidized by electrogenerated active chlorine. For the anodic generation of chlorine the Ti/Pt–Ir material was chosen, due to its previously assessed excellent electrocatalytic properties towards this reaction. The current efficiency of nitrate reduction and energy consumption under different conditions were also evaluated.

Keywords: Electroreduction of nitrates; Nitrite; Electrochemical membrane reactor

Photocatalytic properties of nc-Au/ZnO nanorod composites by Jih-Jen Wu; Chan-Hao Tseng (pp. 51-57).

Photodegradation of methyl orange (MO) under 365-nm irradiation has been performed to investigate the photocatalytic activities of the nc-Au/ZnO nanorod composites in comparison with those of the ZnO nanorods and the ZnO film. The ZnO nanorods and the ZnO film were deposited on the Si substrates using chemical vapor deposition. The apparent first-order rate constant of MO photodegradation using the ZnO nanorods is two orders magnitude larger than that using the ZnO film. Photosyntheses of Au nanoparticles on the ZnO nanorods were conducted in HAuCl₄/ethanol solutions under 365-nm irradiation. The diameters and the densities of the Au nanoparticles formed on the surface of ZnO nanorods are tunable through varying the HAuCl₄ concentration and the irradiation period. The enhancement of the photocatalytic activity for degradation of MO is achieved by loading Au nanoparticles with sizes smaller than 15nm on the ZnO nanorods and is more pronounced as the size of the Au nanoparticles is reduced to 5nm. However, the photocatalytic activity of the nc-Au/ZnO nanorod composite is much lower than that of the Zn nanorods when the diameter of the nc-Au is enlarged to 30nm. The photocatalytic activity of the nc-Au/ZnO nanorods for degradation of MO is dependent on the diameter and the density of the nc-Au.

Keywords: ZnO film; ZnO nanorods; nc-Au/ZnO nanorod composites; Photosynthesis; Methyl orange; Photocatalytic degradation

Multivariate approach to the photo-Fenton process applied to the degradation of winery wastewaters by Maria P. Ormad; Rosa Mosteo; Cristina Ibarz; José L. Ovelleiro (pp. 58-63).

Winery wastewaters, being seasonal and experiencing substantial flow variations, are difficult to treat by conventional biological processes. This work proposes the photo-Fenton reaction in homogeneous phase as an alternative for their purification.Experimental design methodology has been used in order to study the main variables affecting the oxidation process as well as their most relevant interactions.Under energetic conditions the photo-Fenton treatment reached purification levels of up to 95% (measured as total organic carbon). The most influential factors behind organic matter removal are the Fe³⁺ and H₂O₂ dosage. The influence of the initial organic matter concentration and the reaction time is almost negligible for the confidence level selected (90%) in the results analysis.

Keywords: Winery wastewaters; Experimental design; Multivariate analysis; Photo-Fenton processes

Investigation of a Ba_0.5Sr_0.5Co_0.8Fe_0.2O3−_δ based cathode IT-SOFC by Aiyu Yan; Mojie Cheng; Yonglai Dong; Weisheng Yang; Vasiliki Maragou; Shuqin Song; Panagiotis Tsiakaras (pp. 64-71).

A Ba_0.5Sr_0.5Co_0.8Fe_0.2O3−_δ (BSCF) based cathode intermediate temperature solid oxide fuel cell (IT-SOFC) was fabricated and tested. The effect of carbon dioxide on the performance of BSCF cathode was evaluated at temperatures ranging from 450 to 750°C. The current density was recorded at a constant discharge of voltage value and the electrochemical impedance spectra (EIS) measurements were carried out in the absence and in the presence of CO₂ in the oxidant gas line (cathode). It was found that the presence even of relatively small quantities (0.28–3.07%) of CO₂ negatively affects the H₂-IT-SOFC performance. It was shown that as the CO₂ content in the cathode side increases and as the operation temperature decreases, the fuel cell performance is seriously aggravated up to 550°C in a reversible way. A further decrease of the operation temperature deteriorates the SOFC performance irreversibly. However, the cell performance can be recovered after treatment at 800°C in pure oxygen. It was also shown that as the CO₂ content increases, the rate of oxygen electrochemical reduction decreases and the corresponding apparent activation energy increases linearly. The EIS results show that the interface resistance increases dramatically after carbon dioxide is added into the oxidant gas line. It is believed that carbon dioxide and temperature, acting in a synergetic way, decrease at least the cathode activity for oxygen reduction. This behaviour could be attributed to the strong carbon dioxide adsorption on the BSCF surface and to the formation of carbonates at temperatures as low as 500 and 450°C.

Keywords: Intermediate-temperature solid oxide fuel cells (IT-SOFCs); BSCF cathodes; Effect of carbon dioxide

Highly selective carbamation of aliphatic diamines under mild conditions using Sc(OTf)₃ as catalyst and dimethyl carbonate as a phosgene substitute by Monica Distaso; Eugenio Quaranta (pp. 72-80).

Sc(OTf)₃ is an effective catalyst for bis-carbomethoxylation of aliphatic diamines with dimethyl carbonate (DMC) under very mild conditions. At ambient temperature (293K), in the presence of Sc(OTf)₃, aliphatic diamines, such as 1,6-diaminohexane (1), 1,4-diaminobutane (2), 1,3-diaminopropane (3), meta-xylylenediamine (4) and para-xylylenediamine (5), react with DMC to afford the corresponding di-carbamates in high yields. The carbomethoxylation reaction is highly selective (≈100%). Under the used working conditions, side-reactions, such as formation of ureas and/or N-methyl derivatives, are repressed. The starting catalyst, Sc(OTf)₃, modifies during the catalytic process and converts into Sc-methoxo species by losing OTf groups, as the isolation of unprecedented mono-urethane triflic salts, (MeO(O)CNH–R–NH₃)O₃SCF₃ (R=–(CH₂)₆–, meta-C₆H₄(CH₂)₂–), also indicates. The modified catalyst can be recovered at the end of the reaction and recycled.

Keywords: Lewis acids; Dimethyl carbonate; Scandium triflate; Di-carbamates; Carbomethoxylation

Probing the factors affecting structure and activity of the Au/CeO₂ system in total and preferential oxidation of CO by Francesco Arena; Pio Famulari; Giuseppe Trunfio; Giuseppe Bonura; Francesco Frusteri; Lorenzo Spadaro (pp. 81-91).

The effects of the preparation method (deposition–precipitation, co-precipitation, incipient-wetness, combustion) and loading (1–5wt.%) on the structure and redox features of the Au/CeO₂ system have been probed by XRD, TEM and TPR techniques. The catalytic pattern in total (TOX) and preferential (PROX) CO oxidation has been assessed by temperature programmed reaction tests in the range 273–473K. Controlling surface area and residual chlorine, the synthesis route determines the strength of the Au–CeO₂ interaction which, reflecting in a hard reduction of the active phase, hinders the CO oxidation functionality. Chlorine removal by washing treatment in diluted alkaline solutions enables an easy reduction of the active phase, levelling off the TOX and PROX performance of the various systems.

Keywords: Au/CeO; ₂; catalyst; Preparation method; Reduction pattern; Surface area; Chlorine; Dispersion; Total and preferential CO oxidation

Naphthalene total oxidation over metal oxide catalysts by Tomás García; Benjamín Solsona; Stuart H. Taylor (pp. 92-99).

Metal oxide catalysts (CoOx, MnOx, CuO, ZnO, Fe₂O₃, CeO₂, TiO₂, Al₂O₃ and CuZnO) prepared by a precipitation method have been characterised and tested for the total oxidation of naphthalene. The most effective catalyst for naphthalene oxidation was CeO₂ prepared by a homogeneous precipitation method with urea. Moreover, the cerium oxide catalyst showed stable conversion with 100% selectivity to CO₂ with time-on-stream at very low temperatures, 175°C. The total oxidation of propane was also probed using the same range of catalysts and no correlation between naphthalene and alkane oxidation was apparent, indicating that different mechanisms are involved. It was observed that whilst redox properties were the main factor controlling propane total oxidation, the surface area and the strength of the bond between adsorbed molecules and catalyst surface were also important parameters affecting naphthalene catalytic combustion.

Keywords: VOCs; PAHs; Catalytic oxidation; Metal oxides; Cerium oxide

Photocatalytic properties of nanosized Bi₂WO₆ catalysts synthesized via a hydrothermal process by Hongbo Fu; Liwu Zhang; Wenqing Yao; Yongfa Zhu (pp. 100-110).

Nanosized Bi₂WO₆ was synthesized by a hydrothermal crystallization process. The as-prepared samples were characterized by X-ray diffraction, Brunauer–Emmet–Teller surface area and porosity measurements, transmission electron microscopy, Raman spectra, and diffuse reflectance spectroscopy. The photoactivities of the as-prepared samples for the rhodamine-B photodegradation were investigated systematically. As a result, the sample prepared at 180°C exhibited the highest photochemical activity under visible-light irradiation. The further experiments revealed that the catalyst was active in a wide spectral range. Density functional theory calculations suggested that the visible-light response was due to the transition from the valence band formed by the hybrid orbitals of Bi 6s and O 2p to the conduction band of W 5d. The photoactivity of the catalyst in relationship with the hydrothermal temperature, the crystal and band structure were also discussed in detail.

Keywords: Photocatalytic; Nanosized Bi; ₂; WO; ₆; Hydrothermal synthesis; Rhodamine-B; Visible-light

Single-reactor process for sequential aldol-condensation and hydrogenation of biomass-derived compounds in water by C.J. Barrett; J.N. Chheda; G.W. Huber; J.A. Dumesic (pp. 111-118).

A bifunctional Pd/MgO-ZrO₂ catalyst was developed for the single-reactor, aqueous phase aldol-condensation and hydrogenation of carbohydrate-derived compounds, furfural and 5-hydroxymethylfurfural (HMF), leading to large water-soluble intermediates that can be converted to liquid alkanes. The cross aldol-condensation of these compounds with acetone results in formation of water-insoluble monomer (C₈–C₉) and dimer (C₁₃–C₁₅) product species, which are subsequently hydrogenated in the same batch reactor to form water-soluble products with high overall carbon yields (>80%). After a cycle of aldol-condensation followed by hydrogenation, the Pd/MgO-ZrO₂ catalyst undergoes a loss in selectivity by 18% towards heavier product (dimer) during subsequent runs. However, the catalytic activity and dimer selectivity are completely recovered when the catalyst is recycled with an intermediate calcination step at 873K. The optimum temperatures for aldol-condensation of furfural with acetone and for condensation of HMF with acetone are 353 and 326K, respectively, representing a balance between dimer selectivity and overall carbon yield for the process. The product selectivity can be controlled by the molar ratio of reactants. When the molar ratio of furfural-acetone increases from 1:9 to 1:1, the selectivity for the formation of dimer species increases by 31% and this selectivity increases further by 12% when the ratio increases from 1:1 to 2:1. It is likely that this active, stable, and heterogeneous catalyst system can be applied to other base and/or metal catalyzed reactions in the aqueous phase.

Keywords: Renewable energy; Heterogeneous catalysis; Biomass; Aldol-condensation; Hydrogenation

Phototransformation of triclosan in the presence of TiO₂ in aqueous suspension: Mechanistic approach by Salah Rafqah; Pascal Wong-Wah-Chung; Sylvie Nelieu; Jacques Einhorn; Mohamed Sarakha (pp. 119-125).

The photocatalytic degradation of the antimicrobial triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) was studied using different types of TiO₂ suspension photocatalysts (Degussa P25, PC50 and PC 500) and excitation wavelength of 365nm. In all cases, the degradation process mainly involved the formation of hydroxyl radicals. Under our experimental conditions and in aerated solutions, the irradiation in the presence of TiO₂ P25 permitted the evaluation of the half-lifetime to about 10min. The intermediate byproducts were identified by means of HPLC/MS/MS using electrospray (ES) interfacing technique. They were obtained as a result of three main primary processes: (i) homolytic scission of CO bond leading to the formation of 2,4-dichlorophenol and chlorocatechol, (ii) hydroxylation of the phenolic group and (iii) dechlorination process leading to the formation of 5-chloro-2-(4-chlorophenoxyl)phenol. Under prolonged irradiation efficient mineralisation of triclosan solution was observed as evidenced by means of total organic carbon (TOC) evolution as well as chloride anions formation as a function of irradiation time.

Keywords: Triclosan; Titanium dioxide; Antimicrobial; Heterogeneous photocatalysis; Hydroxyl radical; Mineralisation

Supported Pt-Ba NO_x storage-reduction catalysts: Influence of support and Ba loading on stability and storage efficiency of Ba-containing species by M. Piacentini; M. Maciejewski; A. Baiker (pp. 126-136).

A series of supported Pt-Ba NO_x storage-reduction catalysts has been prepared by impregnation of corresponding supported 1wt.% Pt catalysts with Ba(Ac)₂ precursor and subsequent calcination at 500°C. Ceria, zirconia and silica were applied as supports and the Ba loading was varied from 0 to 28wt.%. The Ba-containing phase of these catalysts was systematically investigated concerning stability and NO_x storage efficiency.Temperature programmed reaction-desorption experiments of the catalysts calcined in situ revealed two differently stable barium carbonate phases, low-temperature barium carbonate (LT-BaCO₃) and high-temperature barium carbonate (HT-BaCO₃). The total amount of barium carbonate was highest in Pt-Ba/ceria and Pt-Ba/zirconia, and significantly smaller in the Pt-Ba/alumina reference catalysts, whereas in Pt-Ba/silica barium carbonate was only detected at the highest Ba loading. The relative amount of LT-BaCO₃, which is considered the most efficient Ba-phase for NO_x storage, depended on the support material and the Ba loading. Ceria and zirconia as supports afforded catalysts where the LT-BaCO₃ was the dominant form of barium carbonate. At low Ba loading (4.5wt.%), the barium carbonate phase was exclusively made up of LT-BaCO₃, while with higher loadings the contribution of HT-BaCO₃ increased strongly. NO_x storage measurements indicated a correlation between the relative amount of LT-BaCO₃ and the NO_x storage efficiency. At low Ba loading the efficiency decreased in the following order: ceria>zirconia>alumina>silica, whereas at high Ba loading the storage efficiency of the differently supported catalysts became similar. The different behavior of the Ba-containing phases on the supported Pt-Ba catalysts was traced to the different chemical (basicity) and textural properties of the investigated support materials.

Keywords: NO; _x; storage-reduction catalysts; Pt-Ba/ceria; Pt-Ba/zirconia; Pt-Ba/silica; Pt-Ba/alumina; NO; _x; storage efficiency; Effect of Ba loading; Stability of barium carbonates

Effects of chloride ions on the iron(III)-catalyzed decomposition of hydrogen peroxide and on the efficiency of the Fenton-like oxidation process by Joseph De Laat; Truong Giang Le (pp. 137-146).

The effects of chloride concentration on the rates of decomposition of H₂O₂ by ferric ion and on the rate of oxidation of an organic solute in homogeneous aqueous solution have been investigated. Experiments were carried out in a batch reactor, in the dark, at pH≤3, 25.0±0.5°C and at controlled ionic strength (≤1M). The concentrations of chloride ranged from 0 to 1M ([Fe(III)]₀=0.2 or 1mM, [H₂O₂]₀=1, 10 or 50mM). The spectrophotometric study shows that chloride ions compete with hydrogen peroxide for the complexation of Fe(III) and that H₂O₂ does not form complexes with iron(III)-chlorocomplexes. The kinetic study showed that the rates of decomposition of H₂O₂ decreased in the presence of chloride. The measured rates were accurately predicted by a kinetic model which incorporates the formation of iron(II) and iron(III)-chlorocomplexes and reactions involving Cl₂⁻ radicals. At a fixed pH, the pseudo-first-order rate constants were found to decrease linearly with the molar fraction of Fe(III) complexed with chloride. The kinetic model was also able to predict the rate of oxidation of a probe compound (atrazine) by Fe(III)/H₂O₂ in the presence of chloride. Computer simulations indicate that Cl₂⁻ which represents the predominant radical contributes to the oxidation of atrazine.

Keywords: Fenton reaction; Atrazine; Hydroxyl radical; Dichlorine anion radical; Kinetic modelling

An FTIR study on the formation of NCO surface complexes over Rh/CeO₂ by Tamás Bánsági; Tímea Süli Zakar; Frigyes Solymosi (pp. 147-150).

Fourier transferred infrared spectroscopy combined with mass spectrometry was used to follow the NO+CO reaction and the formation of adsorbed species. It was shown that when the reaction between NO and CO set in two absorption bands appeared in the FTIR spectra of Rh/CeO₂ at 2180 and 2210cm⁻¹, which were not observed following the adsorption of reactants and products. Adsorption of HNCO on pure CeO₂ at 200 and 300K yielded the same spectral features suggesting that these bands belong to adsorbed isocyanate, NCO, species bonded to the CeO₂. These results suggest that the spillover process of NCO from the Rh onto support proceeds even in the case of CeO₂ used as a solid oxidizer in the three-way catalyst. NCO attached to ceria reacts with H₂O resulting in the release of NH₃.

Keywords: NO–CO reaction; Isocyanate formation; Rh/CeO; ₂; catalyst; HNCO adsorption; Spillover of NCO; Reaction of NCO with H; ₂; O; FTIR spectroscopy

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Applied Catalysis B, Environmental (v.66, #1-2)