Check out our New Publishers' Select for Free Articles

Applied Catalysis B, Environmental (v.61, #3-4)

IFC (pp. co2).

FULL TITLE (pp. i).

CONTENTS OF VOLUME (pp. i-ii).

CALENDER (pp. iii).

Catalytic combustion of volatile organic compounds on gold/titanium oxynitride catalysts by M.A. Centeno; M. Paulis; M. Montes; J.A. Odriozola (pp. 177-183).

Catalytic oxidation of n-hexane, benzene and 2-propanol was investigated on Au/TiO_xN_y and Au/TiO₂ catalysts prepared by the deposition–precipitation method and characterized by XRD, TEM and XPS techniques. The dispersion and average size of the gold particles are dependent on the nitrogen content of the support. Calcination of samples leads to a decrease in the nitrogen content of the samples and to gold particle agglomeration. In gold catalysts with high nitrogen content, XPS detects the existence of partially oxidised Au δ⁺ species. The presence of Au δ⁺ or Au⁰ species and the amount and size of gold particles determine the activity towards the catalytic combustion of VOCs of these systems.

Keywords: Volatile organic compounds; Gold catalysts; Catalytic combustion; Titanium oxynitride; n; -Hexane; Benzene; 2-Propanol

Benzene electro-oxidation in a PEMFC for phenol and electricity cogeneration by Rui Cai; Shuqin Song; Baofeng Ji; Weishen Yang; Qin Xin; Gongquan Sun; Savvas Douvartzides; Panagiotis Tsiakaras (pp. 184-191).

In the present investigation, the electrochemically-assisted oxidation of benzene in a H₂–O₂ proton exchange membrane fuel cell (PEMFC), for electricity and phenol cogeneration is studied. Experiments were carried out in a PEMFC electrochemical reactor using Pd black as cathode electrocatalyst at 60 and 80°C, respectively and 1atm back pressure. Indeed, it was found that the only product detected under the examined experimental conditions was phenol. The online GC product analysis revealed that it is impossible to produce phenol when the fuel cell circuit is open ( I=0) under all the examined experimental conditions. When the fuel cell circuit was closed, however, the phenol yield was found to follow a volcano-type dependence on the current of the external circuit. It was found that the maximum phenol yield was 0.35% at 100mA/cm² at 80°C. At the same time, the PEMFC performance was also investigated during the phenol generation process. Furthermore, experiments with the rotating ring disc electrode (RRDE) technique showed that the intermediate oxidation product, i.e. H₂O₂ existed during the oxygen electro-reduction process. The cyclic voltammograms showed that benzene was strongly adsorbed on the Pd surface, leading to a degradation of the PEMFC performance.

Keywords: Benzene; Phenol; PEMFC; Pd black

CO oxidation over CuO_x-CeO₂-ZrO₂ catalysts: Transient behaviour and role of copper clusters in contact with ceria by Maela Manzoli; Roberta Di Monte; Flora Boccuzzi; Salvatore Coluccia; Jan Kašpar (pp. 192-205).

The effects of ZrO₂ content on the CO oxidation activity in a series of CuO_x/Ce_xZr1−_xO₂ ( x=0, 0.15, 0.5, 0.7 and 1) catalysts were investigated, both in the absence and in the presence of H₂, i.e. preferential CO oxidation—PROX. The investigation was performed under light-off conditions to focus the effects of transients and shut-down/start-up cycles on the performance; such phenomena are expected to affect the activity of PROX catalysts in small/delocalised fuel reformers. Evidence has been obtained for a transition from an “oxidized�? towards a “reduced�? state of the catalyst under the simulated PROX reaction conditions as a function of the reaction temperature, leading to different active species under the reaction conditions. Both CO oxidation activity and PROX selectivity appear to be affected by this process. IR characterisation of the surface copper species suggests an important role of reduced cerium sites in close contact with copper clusters on the CO oxidation activity at low temperatures.

Keywords: CeO; ₂; –ZrO; ₂; mixed oxides; CO oxidation over copper catalysts; PROX catalysts; CuO; _x; /CeO; ₂; –ZrO; ₂; IR characterisation of

Catalytic oxidation of alcohols using molecular oxygen mediated by poly(ethylene glycol)-supported nitroxyl radicals by Pedro Ferreira; Emyr Phillips; David Rippon; Shik Chi Tsang (pp. 206-211).

The selective catalytic oxidation of alcohols over a mixture of copper(I) chloride and a number of linear ‘linker-less’ or ‘branched’ poly(ethylene glycol)-supported nitroxyl radicals of the 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) family as a catalyst system has been investigated in the presence of molecular oxygen in a batch reactor. It is found that the activity profile of the polymer-supported nitroxyl radicals is in good agreement with that of low-molecular weight nitroxyl catalysts, for example, allylic and benzylic alcohols are oxidised faster than aliphatic alcohols. The oxidations can be tuned to be highly selective such that aldehydes are the only oxidation products observed in the oxidation of primary alcohols and the oxidations of secondary alcohols yield the corresponding ketones. A strong structural effect of the polymeric nitroxyl species on catalytic activity that is dependent upon their spatial orientation of the nitroxyl radicals is particularly noted. The new soluble macromolecular catalysts can be recovered readily from the reaction mixture by solvent precipitation and filtration. In addition, the recycled catalysts demonstrate a similar selectivity with only a small decrease in activity compared to the fresh catalyst even after five repetitive cycles.

Keywords: Catalytic oxidation; Alcohols; Molecular oxygen

Desulfurization of commercial fuels by π-complexation: Monolayer CuCl/γ-Al₂O₃ by Arturo J. Hern�ndez-Maldonado; Gongshin Qi; Ralph T. Yang (pp. 212-218).

Monolayer CuCl/γ-Al₂O₃ sorbent was studied for desulfurization of a commercial jet fuel (364.3ppmwS) and a commercial diesel (140ppmwS). The sorbent was prepared by means of spontaneous monolayer dispersion methods. Deep desulfurization (sulfur levels of <1ppmw) was accomplished with this sorbent using a fixed-bed adsorber. The CuCl/γ-Al₂O₃ sorbent was capable of removing 6.4 and 11.2mg of sulfur per gram for jet fuel at breakthrough (at <1ppmwS) and saturation, respectively. The same sorbent was capable of removing 0.94 and 1.8mg of sulfur per gram for BP diesel at breakthrough and saturation, respectively. The difference in sulfur capacities for jet fuel and diesel was apparently caused by the difference in concentrations of strongly binding compounds, such as nitrogen heterocycles, heavy (polynuclear) aromatics and fuel additives. In comparison with CuCl/γ-Al₂O₃, Cu(I)Y zeolite has higher sulfur capacities but is less stable and can be easily oxidized to Cu(II)Y by fuel additives (such as oxygenates) and moisture and consequently loses π-complexation ability. However, all these cuprous π-complexation sorbents selectively adsorb thiophenic compounds over aromatics and olefins (as predicted by the high separation factors), which resulted in the observed desulfurization capability. A feasibility study is shown for efficient regeneration of CuCl/γ-Al₂O₃ using ultrasound at ambient temperature. Possible problems associated with desulfurization using π-complexation sorbents for commercial fuels are discussed.

Keywords: Desulfurization; π-Complexation; CuCl/γ-Al; ₂; O; ₃; sorbent; Monolayer dispersion

Microstructure, kinetics and mechanisms of CO₂ catalytic decomposition over freshly reduced nano-crystallite CuFe₂O₄ at 400–600°C by M.H. Khedr; A.A. Farghali (pp. 219-226).

The decomposition of CO₂ was investigated as a process of both industrial and environmental importance. Copper ferrite was obtained by the thermal decomposition of acetate precursors. CuFe₂O₄ were isothermally reduced in H₂ flow at 400–600°C, the isothermal reduction profiles obtained in this study show that a topochemical mode of reduction is done by which the reduction process proceeds. The nano-wires metallic phase of iron (106nm) and copper (56nm), produced from the complete reduction of CuFe₂O₄, were subjected to the direct reoxidation in CO₂ flow at 400–600°C. The reoxidation process was found to be controlled by both the reduction and reoxidation temperatures. CO₂ decomposes to carbon nano-tubes during the reoxidation of the freshly reduced CuFe₂O₄. The prepared, completely reduced and reoxidized CuFe₂O₄ compacts, were characterized by XRD, SEM, TEM and reflected light microscope. For the reoxidation process, it is found that at the initial stages the reaction is controlled by the interfacial chemical reaction mechanism with some contribution to the gaseous diffusion mechanism. On the other hand at the intermediate and final stages the mechanism by which the reoxidation process proceeds was found to be the solid-state diffusion.

Keywords: Nano-crystalline; Nano-wires; Carbon nano-tubes; Copper ferrite; Reduction; Reoxidation; CO; ₂; Kinetics and mechanisms

Photocatalytic degradation of a phenylurea, chlortoluron, in water using an industrial titanium dioxide coated media by Ludovic Lhomme; Stephan Brosillon; Dominique Wolbert; Joseph Dussaud (pp. 227-235).

The degradation of an herbicide, chlortoluron, by UV/TiO₂ photocatalysis in water using industrial titanium dioxide coated non-woven paper was studied. The influence of parameters such as adsorption capacity, initial concentration and TiO₂ implementation (coated or in suspension) was investigated. The results emphasize the importance of operational conditions and reactor geometry on the kinetic degradation rate. The analysis of the first organic by-products suggests that a hydroxyl radical attack occurs on the phenyl ring and methyl groups of the chlortoluron before the opening of the aromatic ring. The fate of hetero-atoms has been investigated. The fates of the two nitrogen atoms in the molecule are different, not only did it depend on their initial oxidation degree, as both had the same oxidation degree, but also on the initial oxidation state of neighboring carbons. The chlorine atoms were completely released as chloride ions. The study of the influence of the oxygen concentration showed the importance of the oxygen mass transfer when designing an industrial photocatalytic reactor. An original calculation process was carried out to evaluate the adsorption constant of oxygen over the whole photocatalysis period and not only in the initial conditions as previously provided. This work points out the necessity of extending the understanding of the efficiency of chlortoluron removal or of the removal of various complex pesticide mixtures found in agricultural wastewater, using alternative, more industrially realistic, reactors.

Keywords: Supported photocatalysis; Oxygen influence; By-products; Water treatment; Chlortoluron

A study of the deactivation by sulfur and regeneration of a model NSR Pt/Ba/Al₂O₃ catalyst by S. Elbouazzaoui; E.C. Corbos; X. Courtois; P. Marecot; D. Duprez (pp. 236-243).

The deactivation by sulfur and regeneration of a model Pt/Ba/Al₂O₃ NO_x trap catalyst is studied by hydrogen temperature programmed reduction (TPR), X-ray diffraction (XRD), and NO_x storage capacity measurements. The TPR profile of the sulfated catalyst in lean conditions at 400°C reveals three main peaks corresponding to aluminum sulfates (∼550°C), “surface�? barium sulfates (∼650°C) and “bulk�? barium sulfates (∼750°C). Platinum plays a role in the reduction of the two former types of sulfates while the reduction of “bulk�? barium sulfates is not influenced by the metallic phase. The thermal treatment of the sulfated catalyst in oxidizing conditions until 800°C leads to a stabilization of sulfates which become less reducible. Stable barium sulfides are formed during the regeneration under hydrogen at 800°C. However, the presence of carbon dioxide and water in the rich mixture allows eliminating more or less sulfides and sulfates, depending on the temperature and time. The regeneration in the former mixture at 650°C leads to the total recovery of the NO_x storage capacity even if “bulk�? barium sulfates are still present on the catalyst.

Keywords: Sulfur; Deactivation; Thermal treatment; Barium; NSR catalyst

The role of Bronstead acidity in poisoning the SCR-urea reaction over FeZSM-5 catalysts by James A. Sullivan; Orla Keane (pp. 244-252).

Two series of FeZSM-5 catalysts prepared from Na⁺ and NH₄⁺ ZSM-5 precursors are studied in the selective reduction of NO_x using NH₃ and urea as reducing agents. All Fe-containing catalysts are active for NO_x reduction in the SCR-NH₃ reaction with ex-NH₄⁺ catalysts being more active than ex-Na⁺ materials and the activity depending (to a minor extent within each series of catalysts) upon [Fe]. Catalysts with Bronstead acid sites also show a small transient deNO_x activity at low temperatures. All catalysts are less active for the SCR-urea reaction but the ex-Na⁺ catalysts retain far more deNO_x activity than the ex-NH₄⁺ materials. NH₃ TPD shows that strongly binding Bronstead acid sites are present on the ex-NH₄⁺ materials and H⁺-treated parent zeolites while Urea TPD shows that the mode of decomposition of urea differs as a function of initial zeolite counter-ion. Urea TPSR shows that the reaction between adsorbed urea and gaseous NO/O₂ is related to [Fe]. It is proposed that the decreased activity of the ex-NH₄⁺ catalysts in the SCR-urea reaction is due to a less favourable mode of decomposition over these catalysts. Furthermore it is suggested that the Bronstead acidity plays some part in this less favoured decomposition.

Keywords: FeZSM-5; deNO; _x; Urea; NH; ₃; TPD

Influence of Pt particle size on catalytic combustion of xylenes on carbon aerogel-supported Pt catalysts by M.N. Padilla-Serrano; F.J. Maldonado-H�dar; C. Moreno-Castilla (pp. 253-258).

Pt catalysts supported on a carbon aerogel with different Pt particle sizes were studied in the combustion of o-xylene and m-xylene. Results found show that the activity of the catalysts increased with larger Pt particle size. In addition, the catalysts were activated during consecutive combustion runs and during time on stream. This activation depends on the Pt particle size and type of xylene isomer. Activation was due to the increase in Pt particle size during reaction. The lower activity of catalysts with smaller Pt particle size was due to the stronger PtO bonds formed during xylene combustion by the smaller Pt particles.

Keywords: Xylene combustion; Pt catalysts; Carbon aerogel supports

Highly photoactive supported TiO₂ prepared by thermal hydrolysis of TiOSO₄: Optimisation of the method and comparison with other synthetic routes by M.C. Hidalgo; D. Bahnemann (pp. 259-266).

Supported TiO₂ on sintered borosilicate glass (100–160μm pore size) was prepared by a synthetic route based on the thermal hydrolysis of titanium oxysulfate (TiOSO₄). An optimisation of the preparation method to obtain more stable and photoactive supported TiO₂ was achieved by the control of the different preparation parameters influencing the final properties of the supported TiO₂.A comparative study with other coatings prepared by sol–gel or hydrolysis methods on sintered glass was performed. The examination of the coatings by scanning electron microscopy (SEM) showed a notably different morphology depending on the preparation method.The photocatalytic activity of the different supported TiO₂ materials was tested for the photooxidation of glucose in water. The optimised supported TiO₂ prepared by thermal hydrolysis of TiOSO₄ exhibited a considerably higher photoactivity than the other studied coatings, reaching values of the photonic efficiencies as high as 7%.The stability and lifetime of the most active supported TiO₂ was tested following the evolution of its photocatalytic activity for more than 5 months of continuous operation. No important decrease of the efficiency could be observed during this time.

Keywords: Supported TiO; ₂; Titanium oxysulfate; Sintered glass; Coatings; Photocatalysis; Long-term stability

A new NO_x storage-reduction electrochemical catalyst by X. Li; P. Vernoux (pp. 267-273).

A new NO_x storage-reduction electrochemical catalyst has been prepared from a polycrystalline Pt film deposited on 8mol% Y₂O₃-stabilized ZrO₂ (YSZ) solid electrolyte. BaO has been added onto the Pt film by impregnation method. The NO_x storage capacity of Pt-BaO/YSZ system was investigated at 350�C and 400�C under lean conditions. Results have shown that the electrochemical catalyst was effective for NO_x storage. When nitric oxides are fully stored, the catalyst potential is high and reaches its maximum. On the other hand, when a part of NO and also NO₂ desorb to the gas phase, the catalyst potential remarkably drops and finally stabilizes when no more NO_x storage occurs but only the reaction of NO oxidation into NO₂. Furthermore, the investigation has clearly demonstrated that the catalyst potential variation versus temperature or chemical composition is an effective indicator for in situ following the NO_x storage-reduction process, i.e. the storage as well as the regeneration phase. The catalyst potential variations during NO_x storage process was explained in terms of oxygen coverage modifications on the Pt.

Keywords: BaO; Platinum; YSZ; Electrochemical catalyst; NO; _x; storage; NO; TPD; Sensor

Performance of fluorine-added CoMoS/Al₂O₃ prepared by sonochemical and chemical vapor deposition methods in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene by Jung Joon Lee; Heeyeon Kim; Jae Hyun Koh; Ara Jo; Sang Heup Moon (pp. 274-280).

The performance of a new type of CoMoS/Al₂O₃ catalyst, with added fluorine and prepared by sonochemical and chemical vapor deposition (CVD) methods, was investigated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The catalyst, which was designed to contain optimum amounts of fluorine and cobalt, exhibited a higher activity, ca. 4.6 times higher activity particularly in the HDS of 4,6-DMDBT, than a fluorine-free catalyst prepared by a conventional impregnation method. The enhanced activity of the new catalyst can be attributed to the cumulative effects of individual factors involved in the catalyst preparation. That is, the use of a sonochemical synthesis led to a high dispersion of small MoS₂ crystallites on the alumina, and the addition of the Co species to the catalyst by CVD caused a close interaction between the Co species and the MoS₂ crystallites to produce numerous CoMoS species, which are the catalytically active species for HDS. The addition of fluorine increased the amounts of acidic sites in the catalyst, which promoted hydrogenation (HYD) route to a greater extent than the direct desulfurization (DDS) route in DBT HDS and both HYD and DDS routes to similar extents in the case of 4,6-DMDBT HDS. Accordingly, the addition of fluorine led to a greater increase in catalytic activity for 4,6-DMDBT HDS than for DBT HDS.

Keywords: Hydrodesulfurization; Fluorine; Sonochemistry; Chemical vapor deposition; Dibenzothiophene; 4,6-Dimethyldibenzothiophene; Br�nsted acidity

Role of acidity on the hydrolysis of dimethyl ether (DME) to methanol by Troy A. Semelsberger; Kevin C. Ott; Rodney L. Borup; Howard L. Greene (pp. 281-287).

The activity of dimethyl ether (DME) hydrolysis was investigated over a series of solid acid and non-acid catalysts, zeolite Y [Si/Al=2.5 and 15: denoted Y(Si/Al)], zeolite ZSM-5 [Si/Al=15, 25, 40, and 140: denoted Z(Si/Al)], silica, zirconia, γ-alumina, and BASF K3-110 (commercial Cu/ZnO/Al₂O₃ catalyst). Dimethyl ether hydrolysis was carried out in an isothermal packed-bed reactor at ambient pressure.Acid catalyzed dimethyl ether hydrolysis is equilibrium limited. All solid acid catalysts, with the exception of ZrO₂, attained equilibrium-limited conversions in the temperature range of interest (125–400°C). Z(15), Z(25), and Z(40) reached equilibrium conversions at 200°C, while Z(140), Y(15), and Y(2.5) reached equilibrium at 275°C. γ-Alumina, the most active non-zeolite solid acid, attained equilibrium at 350°C. Silica and BASF K3-110 were both ineffective in converting dimethyl ether to methanol. The observed activity trend for DME hydrolysis to methanol as a function of Si–Al ratio and catalyst type was:Z(15)Z(25)Z(40)>Z(140)Y(15)>Y(2.5)≫γ-Al2O3>ZrO2.

Keywords: Dimethyl ether; Hydrolysis; Zeolites; Methanol; Alumina; Zirconia; Bronsted acidity; Acid site strength; Hydrophobicity; ZSM-5; Y

Active sites of Cu-ZSM-5 for the decomposition of acrylonitrile by Tetsuya Nanba; Shouichi Masukawa; Atsushi Ogata; Junko Uchisawa; Akira Obuchi (pp. 288-296).

The catalytic decomposition of acrylonitrile (AN) over Cu-ZSM-5 prepared with various Cu loadings was investigated. AN conversion, during which the nitrogen atoms in AN were mainly converted to N₂, increased as Cu loading increased. N₂ selectivities as high as 90–95% were attained. X-ray diffraction measurements (XRD) and temperature-programmed reduction by H₂ (H₂-TPR) showed the existence of bulk CuO in Cu-ZSM-5 with a Cu loading of 6.4wt% and the existence of highly dispersed CuO in Cu-ZSM-5 with a Cu loading of 3.3wt%. Electron spin resonance measurements revealed that Cu-ZSM-5 contains three forms of isolated Cu²⁺ ions (square-planar, square-pyramidal, and distorted square-pyramidal). The H₂-TPR results suggested that in Cu-ZSM-5 with a Cu loading of 2.9wt% and below, Cu⁺ existed even after oxidizing pretreatment. The activity of AN decomposition over Cu/SiO₂ suggested that CuO could form N₂, but, independent of the CuO dispersion, nitrogen oxides (NO_x) were formed above 350°C. Cu⁺ and the square-pyramidal and distorted square-pyramidal forms of Cu²⁺ showed low activity for AN decomposition. Temperature-programmed desorption of NH₃ suggested that N₂ formation from NH₃ proceeded on Cu²⁺, resulting in the formation of Cu⁺. The Cu⁺ ions were oxidized to Cu²⁺ at around 300°C. Thus, high N₂ selectivity over Cu-ZSM-5 with a wide range of temperature was probably attained by the reaction over the square-planar Cu²⁺, which can be reversibly reduced and oxidized.

Keywords: Acrylonitrile; N; ₂; Cu-ZSM-5; CuO; Square-planar Cu; ²⁺

Catalyzed traps for diesel soot abatement: In situ processing and deposition of perovskite catalyst by S. Biamino; P. Fino; D. Fino; N. Russo; C. Badini (pp. 297-305).

The present paper deals with the preparation of catalytic filters for Diesel particulate removal by developing an in situ solution combustion synthesis method. Lanthanum chromite perovskite catalyst has been deposited on silicon carbide and cordierite honeycombs with the aim to investigate the influence of the starting solution containing catalyst precursors on the coating characteristics. SEM, XRD and EDX analyses have been carried out in order to evaluate the homogeneity and the thickness of the catalyst layer. In particular, using concentrated solutions, a single combustion synthesis step was found to be sufficient to obtain a continuous catalyst film on the support.Pressure drop evaluations and adhesion tests have also been performed thus verifying the possibility to insert this kind of catalyzed traps on the diesel exhaust gas lines. The homogeneity and the high adherence of the deposited catalyst layer, as well as the simplicity and the rapidity of the method, prove its suitability for immediate technological applications.

Keywords: Combustion synthesis; Honeycomb monoliths; Coating; Perovskite; Catalyst deposition

Effect of operating conditions on the reduction of nitrous oxide by propane over a Fe-zeolite monolith by E. Ruiz-Mart�nez; J.M. S�nchez-Herv�s; J. Otero-Ruiz (pp. 306-315).

Fluidised bed combustion is an important source of nitrous oxide emissions. The influence of different operating parameters, such as catalyst volume, temperature, gas hourly space velocity, and hydrocarbon addition, on the activity, selectivity, and poisoning tolerance of a Fe-ZSM-5 monolith for the nitrous oxide selective catalytic reduction, has been investigated under realistic conditions, at bench scale.Both in the absence or in the presence of poisons, such as H₂O, NO, and SO₂, the optimisation of operating conditions gives rise to a broadening of the temperature window for N₂O reduction, making it more compatible with real application conditions, with a simultaneous reduction in hydrocarbon fugitive emission, resulting in an environmental friendly process.Excessively high reaction temperatures seem to be needed to obtain an acceptable level of N₂O decomposition. On the contrary, high N₂O reduction conversions are obtained, even in the presence of poisons and at relatively low temperatures, which is the preferred situation in the processes of pollutants removal from stationary combustion sources.The optimum value of C₃H₈/N₂O ratio to be used for reducing N₂O over the catalyst system seems to be about the unity, since higher N₂O and C₃H₈ conversions and lower hydrocarbon unwanted emissions are attained, with a low consume of propane as selective reductant.

Keywords: Selective catalytic reduction; Nitrous oxide; Fe-ZSM-5; Propane; Fluidised bed combustion; Space velocity; Water; Nitric oxide; Sulphur dioxide

Thermal-catalytic degradation kinetics of polypropylene over BEA, ZSM-5 and MOR zeolites by Ali Durmuş; S. Naci Koç; G. Selda Pozan; Ahmet Kaşgöz (pp. 316-322).

In this study, thermal degradation of additive-free polypropylene powder over different type of zeolite catalysts was investigated. BEA, ZSM-5 and MOR with different surface areas, pore structures, acidities and Si/Al molar ratios were used as solid catalysts for degradation of polypropylene (PP). Degradation rate of the PP over zeolites was studied by thermogravimetric analysis (TGA) employing four different heating rates and apparent activation energies of the processes were determined by the Kissinger equation. The catalytic activity of zeolites decreases as BEA>ZSM-5a (Si/Al=12.5)>ZSM-5b (Si/Al=25)>MOR depending on pore size and acidity of the catalysts. On the other hand, initial degradation is relatively faster over MOR and BEA than that over both ZSM-5 catalysts depending on the apparent activation energy. It can be concluded that acidity of the catalyst is the most important parameter in determining the activity for polymer degradation process as well as other structural parameters, such as pore structure and size.

Keywords: Polypropylene; Catalytic degradation; Zeolite; Acidity

Study of the copper leaching in the wet oxidation of phenol with CuO-based catalysts: Causes and effects by A. Santos; P. Yustos; A. Quintanilla; G. Ruiz; F. Garcia-Ochoa (pp. 323-333).

Catalytic wet oxidation of phenol as a model pollutant has been performed in a three phase fixed-bed reactor (FBR) by using a commercial catalyst based on copper oxide in order to analyze the variables affecting significantly the copper leaching. It has been found that temperature has an almost negligible influence in the range studied (70–160°C). On the contrary, an important effect of the pH value was noticed. The copper leaching reduces when the pH of the solution fed to the reactor increases, being almost negligible at pH≥5. Moreover, the composition of the reaction media also influences the leaching. Higher copper concentrations than those expected by the effect of the acid aqueous media have been measured in the reactor effluent when phenol, catechol, hydroquinone, p-benzoquinone and maleic acid are present in the reaction media. On the contrary, oxalic acid has a negative influence on the leaching, since it captures the copper in solution to form copper oxalate which precipitates on the catalyst surface. For a previously acidified medium, the acetic and formic acids do not have any other effect on the copper leaching. It has been also demonstrated that as copper in solution decreases, so does phenol conversion, because the homogeneous catalysis contributes significantly to the oxidation reactions even in fixed-bed reactors.

Keywords: Catalytic wet oxidation; Copper oxide; Leaching; Phenol; Fixed-bed reactor

A novel catalyst for diesel soot oxidation by D. Uner; M.K. Demirkol; B. Dernaika (pp. 334-345).

In this study, cobalt and lead based mixed oxide catalysts were tested for their soot oxidation ability. In addition to a mixed oxide formerly marketed as ceramic paint, a home made set was also prepared by incipient wetness impregnation of a cobalt oxide powder with a lead acetate solution and subsequent calcination. The materials investigated in this study were shown to decrease the peak combustion temperature of home made soot from 500 to 385�C in air. Soot oxidation tests under inert (N₂) atmospheres revealed that the oxidation took place by using the lattice oxygen of the catalyst. Reaction temperature could be further decreased when these mixed oxide catalysts were impregnated with platinum. An optimum platinum loading was determined as 0.5wt% based on the peak combustion temperature of the soot. The role of Pt was to assist the oxygen transfer from the gas phase to the lattice. It was observed that NO₂ is a better oxidizing agent as compared to air whereas NO had hardly any activity against soot oxidation reaction. When the mixed oxide catalyst was impregnated with platinum, the peak combustion temperature was measured as 310�C in the presence of NO_x and air. The catalyst's unique performance was in terms of the rate of soot oxidation. Under the experimental conditions studied here, the soot oxidation was so facile that the oxygen in the gas phase was completely depleted. This stream of oxygen depleted and CO enriched gas phase can be used to reduce NO_x in the presence of a downstream or a co-catalyst.

Keywords: Soot oxidation; Cobalt oxide; Lead oxide; Platinum; Molten catalyst

Reduced formation of undesirable by-products from photocatalytic degradation of trichloroethylene by Toshifumi Tanimura; Atsushi Yoshida; Suzuko Yamazaki (pp. 346-351).

Photocatalytic degradation of trichloroethylene (TCE) was investigated using a tubular photoreactor packed with TiO₂ powders prepared by sol–gel techniques. Powders of the following metals: Cr, Fe, Ni, Cu and Pt, or Ca(OH)₂ were uniformly mixed with the TiO₂ powders and then their effect on the formation of COCl₂, CHCl₃, and CHCl₂COCl as by-products was examined. Concentrations of COCl₂ and CHCl₃ were determined in a product gas stream by GC/MS while CHCl₂COCl accumulated on the catalyst surface. When the catalysts were immersed in water after TCE photodegradation, the formation of Cl^- and CHCl₂COO⁻ ions was confirmed by ion-chromatography. Of the chemicals tested, only Cu and Ca(OH)₂ inhibited the formation of the chlorinated by-products. With increasing Cu and Ca(OH)₂ content, TCE conversion decreased while the stoichiometric ratio ([CO₂]_formed/[TCE]_degraded) increased. Concentrations of COCl₂, CHCl₃, and CHCl₂COCl decreased with increasing Cu and Ca(OH)₂ content. Especially, the formation of COCl₂ was remarkably suppressed with Ca(OH)₂.

Keywords: Photocatalytic degradation; Trichloroethylene; Sol–gel technique

Corrigendum to “Complete hydrodechlorination of chlorobenzene and its derivatives over supported nickel catalysts under liquid phase conditions�? [Appl. Catal. B: Environ. 60 (2005) 131–139] by Wenhai Wu; Jie Xu; Ryuichiro Ohnishi (pp. 352-352).

Sections

Personal tools

Applied Catalysis B, Environmental (v.61, #3-4)

Sections

Personal tools

Local resources

Applied Catalysis B, Environmental (v.61, #3-4)