Applied Catalysis B, Environmental (v.63, #3-4)

IFC (CO2).



Hydrodehalogenation using Pd catalysts has proved to be an efficient reaction for water detoxification. In the present study, reaction rates for a variety of halogenated hydrocarbons with hydrogen as reductant in aqueous catalyst suspensions have been measured. Structure–reactivity considerations allow the prediction of reactivities of various halogenated organic compounds in water clean-up processes. The correlation of C―Cl bond strength with the hydrodechlorination rate earlier reported was reassessed. In contrast to straightforward structure–reactivity correlations found for chloroalkanes, hydrodehalogenation rates of chloroethenes and halobenzenes do not follow the order of the C―X bond strength. Here, the addition of an activated hydrogen species from the catalyst to the unsaturated hydrocarbon seems to be the rate-determining step.For pollutant mixtures, hydrodehalogenation rates were influenced by competition for Pd surface sites. Competitors diminish reaction rates depending on their sorption strength towards the Pd surface. Substances subject to extremely slow hydrodehalogenation (such as methylene chloride and fluorobenzene) showed no marked influence on other competitors. The heavier halogens, bromine and iodine (whether as R–X or as X), dominate all competing effects. However, no self-poisoning of the catalyst for hydrodehalogenation of iodo- and bromohydrocarbons occurred in the water phase. This makes it possible to reduce these halogenated compounds at reasonable rates over Pd catalysts.Under optimal conditions, the activity of Pd catalysts is so high that external and intraparticle mass transfer limitations cannot be ruled out for hydrodehalogenation of many substrates in aqueous catalyst suspensions.
Keywords: Catalytic hydrodehalogenation; Palladium catalysts; Structure–reactivity relationship; Surface competition;

The physicochemical, surface and catalytic properties of 10 and 20 wt% CuO, NiO or (CuO–NiO) supported on cordierite (commercial grade) calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at −196 °C and CO oxidation by O2 at 220–280 °C. The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg2Al4Si5O18). Loading of 20 wt% CuO or NiO on the cordierite surface followed by calcination at 350 °C led to dissolution of a limited amount of both CuO and NiO in the cordierite lattice. The portions of CuO and NiO dissolved increased upon increasing the calcination temperature. Treating a cordierite sample with 20 wt% (CuO–NiO) followed by heating at 350 °C led to solid–solid interaction between some of the oxides present yielding nickel cuprate. The formation of NiCuO2 was stimulated by increasing the calcination temperature above 350 °C. However, raising the temperature up to ≥550 °C led to distortion of cuprate phase. The chemical affinity towards the formation of NiCuO2 acted as a driving force for migration of some of copper and nickel oxides from the bulk of the solid towards their surface by heating at 500–700 °C. The S BET of cordierite increased several times by treating with small amounts of NiO, CuO or their binary mixtures. The increase was, however, less pronounced upon treating the cordierite support with CuO–NiO. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 450–700 °C exhibited the highest catalytic activity due to formation of the nickel cuprate phase. However, the catalytic activity of the mixed oxides system reached a maximum limit upon heating at 500 °C then decreased upon heating at temperature above this limit due to the deformation of the nickel cuprate phase.
Keywords: Cordierite; Nickel cuprate; Copper oxide; Nickel oxide; CO oxidation; Migration; Solid solution;

Gold catalysts supported on mesoporous zirconia for low-temperature water–gas shift reaction by V. Idakiev; T. Tabakova; A. Naydenov; Z.-Y. Yuan; B.-L. Su (178-186).
Mesoporous ZrO2 with high surface area and uniform pore size distribution, synthesized by surfactant templating through a neutral [C13(EO)6–Zr(OC3H7)4] assembly pathway, was used as a support of gold catalysts prepared by deposition–precipitation method. The supports and the catalysts were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, N2 adsorption analysis, temperature programmed reduction and desorption. The catalytic activity of gold supported on mesoporous zirconia was evaluated in water–gas shift (WGS) reaction at wide temperature range (140–300 °C) and at different space velocities and H2O/CO ratios. The catalytic behaviour and the reasons for а reversible deactivation of Au/mesoporous zirconia catalysts were studied. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new Au/mesoporous zirconia catalyst was compared to the reference Au/TiO2 type A (World Gold Council), revealing significantly higher catalytic activity of Au/mesoporous zirconia catalyst. It is found that the mesoporous zirconia is a very efficient support of gold-based catalyst for the WGS reaction.
Keywords: Gold catalysts; Mesoporous zirconia; Water–gas shift reaction;

Direct ethanol fuel cells (DEFCs) belong to the family of proton exchange membrane fuel cells (PEMFCs), in which ethanol is directly used as the fuel. In the present work, the main aspects related to DEFCs such as electrocatalysts, membrane electrode assembly (MEA) preparation and their corresponding effects on the total cell performance are summarized and discussed. Furthermore, the issues about the disadvantages such as ethanol crossover and the electrolyte membrane's thermal and mechanical stability, as well as the challenges for DEFC's rapid development and commercialization are addressed.
Keywords: Direct ethanol PEMFC (DE-PEMFC); Electrocatalysts for ethanol electrooxidation; Membrane electrode assembly (MEA); Ethanol crossover;

Kinetics of the water–gas shift reaction over nanostructured copper–ceria catalysts by Henrik Kušar; Stanko Hočevar; Janez Levec (194-200).
Water–gas shift reaction was studied over two nanostructured Cu x Ce1−x O2−y catalysts: a Cu0.1Ce0.9O2−y catalyst prepared by a sol–gel method and a Cu0.2Ce0.8O2−y catalyst prepared by co-precipitation method. A commercial low temperature water–gas shift CuO–ZnO–Al2O3 catalyst was used as reference. The kinetics was studied in a plug flow micro reactor at an atmospheric pressure in the temperature interval between 298 and 673 K at two different space velocities: 5.000 and 30.000 h−1, respectively. Experimentally estimated activation energy, E af, of the forward water–gas shift reaction at CO/H2O = 1/3 was 51 kJ/mol over the Cu0.1Ce0.9O2−y , 34 kJ/mol over the Cu0.2Ce0.8O2−y and 47 kJ/mol over the CuO–ZnO–Al2O3 catalyst. A simple rate expression approximating the water–gas shift process as a single reversible surface reaction was used to fit the experimental data in order to evaluate the rate constants of the forward and backward reactions and of the activation energy for the backward reaction.
Keywords: Catalysis; Kinetics; Water–gas shift; Catalyst; Ceria; Copper; CO; H2; Fuel cell;

On the promotional effect of Pd on the propene-assisted decomposition of NO on chlorinated Ce0.68Zr0.32O2 by Cyril Thomas; Olivier Gorce; Céline Fontaine; Jean-Marc Krafft; Françoise Villain; Gérald Djéga-Mariadassou (201-214).
The selective catalytic reduction (SCR) of NO x assisted by propene is investigated on Pd/Ce0.68Zr0.32O2 catalysts (Pd/CZ), and is compared, under identical experimental conditions, with that found on a Pd/SiO2 reference catalyst. Physico-chemical characterisation of the studied catalysts along with their catalytic properties indicate that Pd is not fully reduced to metallic Pd for the Pd/CZ catalysts. This study shows that the incorporation of Pd to CZ greatly promotes the reduction of NO in the presence of C3H6. These catalysts display very stable deNO x activity even in the presence of 1.7% water, the addition of which induces a reversible deactivation of about 10%. The much higher N2 selectivity obtained on Pd/CZ suggests that the lean deNO x mechanism occurring on these catalysts is different from that occurring on Pd0/SiO2. A detailed mechanism is proposed for which CZ achieves both NO oxidation to NO2 and NO decomposition to N2, whereas PdO x activates C3H6 via ad-NO2 species, intermediately producing R-NO x compounds that further decompose to NO and C x H y O z . The role of the latter oxygenates is to reduce CZ to provide the catalytic sites responsible for NO decomposition. The proposed C3H6-assisted NO decomposition mechanism stresses the key role of NO2, R-NO x and C x H y O z as intermediates of the SCR of NO x by hydrocarbons.
Keywords: CO-FTIR; XANES; Lean deNO x ; Mechanism; C3H6; Pd catalysts; Ceria–zirconia; TPD of NO x ;

H2O2 used in the photo-Fenton reaction with iron catalyst can accelerate the oxidation of Fe2+ to Fe3+ under UV irradiation and in the dark (in the so called dark Fenton process). It was proved that conversion of phenol under UV irradiation in the presence of H2O2 predominantly produces highly hydrophilic products and catechol, which can accelerate the rate of phenol decomposition. However, while H2O2 under UV irradiation could decompose phenol to highly hydrophilic products and dihydroxybenzenes in a very short time, complete mineralization proceeded rather slowly. When H2O2 is used for phenol decomposition in the presence of TiO2 and Fe–TiO2, decrease of OH• radicals formed on the surface of TiO2 and Fe–TiO2 has been observed and photodecomposition of phenol is slowed down. In case of phenol decomposition under UV irradiation on Fe–C–TiO2 photocatalyst in the presence of H2O2, marked acceleration of the decomposition rate is observed due to the photo-Fenton reactions: Fe2+ is likely oxidized to Fe3+, which is then efficiently recycled to Fe2+ by the intermediate products formed during phenol decomposition, such as hydroquinone (HQ) and catechol.
Keywords: Phenol decomposition; Phenol conversion; Photo-Fenton reaction; H2O2;

A lost of culturability of bacteria Escherichia coli K12 was observed after exposition to a solar simulator (UV–vis) in a laboratory batch photoreactor. The bacterial inactivation reactions have been carried out using titanium dioxide (TiO2) P25 Degussa and FeCl3 as catalysts. At the starting of the treatment, the suspensions were at their “natural” pH. An increase in the efficiency in the water disinfection was obtained when some advanced oxidation processes such as UV–vis/TiO2, UV–vis/TiO2/H2O2, UV–vis/Fe3+/H2O2, UV–vis/H2O2 were applied. The presence of H2O2 accelerates the rate of disinfection via TiO2. The addition of Fe3+ (0.3 mg/l) to photocatalytic system decreases the time required for total disinfection (<1 CFU/ml), for TiO2 concentrations ranging between 0.05 and 0.5 g/l. At TiO2 concentrations higher than 0.5 g/l the addition of Fe3+ does not significantly increase the disinfection rate. The systems: Fenton (H2O2/Fe3+/dark), H2O2/dark, H2O2/TiO2/dark showed low disinfection rate. The effective disinfection time (EDT24) was reached after 60 and 30 min of illumination for the Fe3+ and TiO2 photoassisted systems, respectively. EDT24 was not reached for the system in the absence of catalyst (UV–vis). The effect on the bacterial inactivation of different mixture of chemical substance added to natural water was studied.
Keywords: Solar water disinfection; TiO2; Iron photoassisted reaction; Photocatalysis; Water disinfection; E. coli K12; Photo-Fenton; EDT24;

Formation and stability of barium aluminate and cerate in NO x storage-reduction catalysts by Maria Casapu; Jan-Dierk Grunwaldt; Marek Maciejewski; Meike Wittrock; Ulrich Göbel; Alfons Baiker (232-242).
The formation and stability of BaAl2O4 and BaCeO3 in Pt-Ba/Al2O3 and Pt-Ba/CeO2 based NO x storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO3. The formation of BaAl2O4 started above 850 °C, whereas the formation of BaCeO3 was already observed at 800 °C and was faster than that of BaAl2O4. The stability of BaAl2O4 and BaCeO3 in various liquid and gaseous atmospheres was different. BaAl2O4 was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO3)2 and γ-alumina in the presence of HNO3, whereas BaCeO3 was decomposed to much lower extent under these conditions. Interestingly, BaCeO3 was transformed to Ba(NO3)2/CeO2 in the presence of NO2/H2O at 300–500 °C. Also, the presence of CO2 led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NO x -storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts.
Keywords: NO x storage-reduction catalyst; Pt-Ba/Al2O3; Pt-Ba/CeO2; Barium aluminate; Barium cerate; Thermal stability; Ageing; X-ray diffraction; Thermal analysis; X-ray absorption spectroscopy; Regeneration;

Degradation of 4-chloro-2-methylphenol (PCOC), a refractory toxic chemical emitted to the environment from the industrial production of phenoxy herbicides was studied in aqueous solution. Electro-Fenton and photoelectro-Fenton processes were used as the degradation methods. H2O2, produced by the reduction of oxygen at carbon cathode reacted with dissolved metal ions to form hydroxyl radicals, which in turn reacted with PCOC sequentially to degrade the aromatic ring. The effects of using different [Fe2+]/[PCOC]0 and the effect of replacing Fe2+ by Mn2+ ion have been examined. It was found that degradation rate was increased with increasing [Fe2+]/[PCOC]0 ratio from 2 to 4. However, the total charge utilized during the treatment was also increased. The efficiency of PCOC degradation was observed to be higher when Mn2+ was used as the catalyst. The mineralization of aqueous solutions of PCOC, withdrawn from the reactor at certain time interval, has been followed by total organic carbon (TOC) decay and dechlorination. A fast and complete degradation of the aromatic ring was achieved in photoelectro-Fenton system. 41.7% TOC decay and complete dechlorination were observed by consuming only 141.4 C electrical charge during a 300 min photoelectron-Fenton treatment. In the case of electro-Fenton system, 280.7 C electrical charge was consumed during 450 min of electrolysis to attain a similar degradation of PCOC. 14.9% TOC removal and 89.3% dechlorination have been obtained in this system under the applied conditions.
Keywords: Electro-Fenton; UV light; 4-chloro-2-methylphenol; Electrical charge; Degradation;

Gallic acid water ozonation using activated carbon by Fernando J. Beltrán; Juan F. García-Araya; Inés Giráldez (249-259).
The ozonation of gallic acid in water in the presence of activated carbon has been studied at pH 5. Hydrogen peroxide, ketomalonic and oxalic acids were identified as by-products. The process involves two main periods of reaction. The first period, up to complete disappearance of gallic acid, during which ozonation rates are slightly improved by the presence of activated carbon. The second one, during which activated carbon plays an important role as promoter, and total mineralization of the organic content of the water is achieved. The organic matter removal is due to the sum of contributions of ozone direct reactions and adsorption during the first period and to a free radical mechanism likely involving surface reactions of ozone and hydrogen peroxide on the carbon surface during the second period. There is a third transition period where by-products concentration reach maximum values and ozonation is likely due to both direct and free radical mechanisms involving ozone and adsorption. Discussion on the mechanism and kinetics of the process is also presented both for single ozonation and activated carbon ozonation.
Keywords: Activated carbon; Ozone; Gallic acid; Ozonation by-products; Heterogeneous activated carbon ozonation; Water ozonation;

Inhibition effect of H2O on V2O5/AC catalyst for catalytic reduction of NO with NH3 at low temperature by Zhanggen Huang; Zhenyu Liu; Xianlong Zhang; Qingya Liu (260-265).
The inhibition effect of H2O on V2O5/AC catalyst for NO reduction with NH3 is studied at temperatures up to 250 °C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses. The results show that H2O does not reduce NO and NH3 adsorption on V2O5/AC catalyst surface, but promotes NH3 adsorption due to increases in Brønsted acid sites. Many kinds of NH3 forms present on the catalyst surface, but only NH4 + on Brønsted acid sites and a small portion of NH3 on Lewis acid sites are reactive with NO at 250 °C or below, and most of the NH3 on Lewis acid sites does not react with NO, regardless the presence of H2O in the feed gas. H2O inhibits the SCR reaction between the NH3 on the Lewis acid sites and NO, and the inhibition effect increases with increasing H2O content. The inhibition effect is reversible and H2O does not poison the V2O5/AC catalyst.
Keywords: H2O; V2O5/AC catalyst; NO; NH3; Inhibition effect;

The commercially available TiO2-catalyst (Degussa P25) was modified with nanosized platinum and silver particles by the photoreduction method to obtain different noble metal loading (0.5 and 1 wt.%). The characterization of the synthesized catalysts was carried out by the BET method, XPS, TEM and the adsorption of the model pollutant. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles. The photocatalytic activity of TiO2, modified with noble metal, is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied model pollutant is due to the formation of Schottky barriers on the metal–semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination.
Keywords: Platinum; Silver; TiO2; Photocatalytic decomposition; Oxalic acid; XPS; TEM;

Carbon-modified TiO2 photocatalyst by ethanol carbonisation by M. Janus; M. Inagaki; B. Tryba; M. Toyoda; A.W. Morawski (272-276).
The new photocatalysts based on commercially available titanium dioxide powders: Tytanpol A11 (Police, Poland), pure anatase and P-25 (Degussa, Germany) containing about 20% rutile were modified by carbon via ethanol carbonisation. Titanium dioxides were heated at different temperature from 150 to 400 °C for 1 h in an atmosphere of ethanol vapour. The photocatalytic activity of carbon-modified TiO2 was studied by oxidation of phenol in water under UV and artificial solar light irradiation. With increasing of carbon content in TiO2 photocatalysts the activity for phenol decomposition under UV light was decreasing but that under visible light was stable. Turbidity of the slurry solution decreased with increasing of carbon content for all prepared photocatalysts because of the change of their surface character from hydrophilic to hydrophobic.
Keywords: Carbon-modified TiO2; Photocatalysis; Solar light;

Production of clean transportation fuels and lower olefins from Fischer-Tropsch Synthesis waxes under fluid catalytic cracking conditions by Xander Dupain; Ralph A. Krul; Colin J. Schaverien; Michiel Makkee; Jacob A. Moulijn (277-295).
The potential of Fischer-Tropsch Synthesis (FTS) waxes as a feedstock for fluid catalytic cracking (FCC) has been evaluated with a once-through microriser reactor operating under realistic conditions. The highly paraffinic feedstock has a high reactivity and can be converted under industrial conditions to a high extent (>90 wt%). The product distribution can be optimised by the process parameters and catalyst formulation. A high gasoline fraction (70 wt%) with a very low aromatics concentration can be obtained. As a result of the formation of i-paraffins, n-olefins and i-olefins the gasoline is expected to possess an acceptable octane number. The reaction scheme derived predicts that the degree of branching in the paraffinic diesel-range product is lower than that of the gasoline-range product and that a relatively good diesel is expected. Due to the absence of sulfur and nitrogen in the feed extremely clean transportation fuels are obtained. The addition of ZSM-5 to an equilibrium catalyst allows the production of significant amounts of light olefins, in particular propene (16 wt%) and butenes (15 wt%).
Keywords: Fluid catalytic cracking (FCC); Fischer-Tropsch Synthesis (FTS); Diesel; Gasoline (low-sulfur, low-nitrogen, low-aromatic, low-naphthenic); LPG (propene, i-butene, butenes); ZSM-5;

Catalytic oxidation of hydrogen sulfide by dioxygen on CoN4 type catalyst by A. Goifman; J. Gun; F. Gelman; I. Ekeltchik; O. Lev; J. Donner; H. Börnick; E. Worch (296-304).
A new catalyst based on the formation of carbon supported “CoN4” structures by heat treatment of Co(CH3COO)2 and imidazole impregnated carbon black is introduced. The performance of the new catalyst is compared to the performance of other catalysts including activated carbon powder, granular activated carbon, and pyrolysed cobalt(II) mesotetra-4-methoxyphenylporphyrin. The optimized form of the new catalyst outperforms all these catalysts. The underlying concept is borrowed from fuel cell technology, which uses electrocatalysts that activate triplet dioxygen and facilitate its reduction. The same concept is used to reduce oxygen by hydrogen sulfide. In electrochemistry oxygen reduction is carried out by heterogeneous electron transfer, whereas in dehydrosulfurization the reduced sulfur moieties serve as the electron donors. We postulate that the reason for the improved performance of the new catalyst compared to pyrolysed carbon supported cobalt porphyrin, which is also a Me–N4 type catalyst, stems from the ability to load a larger amount of cobalt chelates rather than from a change of oxidation mechanism.
Keywords: Hydrogen sulfide; Cobalt porphyrin; Carbon supported catalyst; Oxidation; Drinking water; Me–N4;

Ag-ZnO catalysts for UV-photodegradation of methylene blue by Murray J. Height; Sotiris E. Pratsinis; Okorn Mekasuwandumrong; Piyasan Praserthdam (305-312).
High surface area Ag-ZnO catalysts have been made by flame spray pyrolysis (FSP) and characterized by X-ray diffraction (XRD), nitrogen adsorption, UV–vis spectroscopy and electron microscopy (SEM and transmission electron microscopy (TEM)) combined with energy dispersive X-ray spectroscopy (EDXS) for elemental mapping. Silver metal clusters deposited directly on ZnO nanocrystals were obtained from this process. The Ag loading (1–5 at.%) controlled the Ag cluster size from 5 to 25 nm but did not influence the ZnO crystal size. Photodegradation of 10 ppm methylene blue (MB) solution was used to evaluate the performance of these FSP-made Ag-ZnO and was compared to wet-made Ag-ZnO and reference titania photocatalysts. The rate of photodegradation was optimal for Ag loading around 3 at.%. The best photocatalytic performance was exhibited by flame-made Ag-ZnO produced at the longest high-temperature residence times having high crystallinity as determined by XRD and UV–vis.
Keywords: Silver; Zinc oxide; Flame spray pyrolysis; Methylene blue; Reaction kinetics;