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Applied Catalysis B, Environmental (v.70, #1-4)

IFC Editorial Board (pp. co2).

Editorial Board (pp. i).

Special Issue Contents List (pp. iv-vii).

4th International Conference on Environmental Catalysis—ICEC-4 by Roger Gläser; Johannes A. Lercher; Klaus-Dieter Vorlop; Jens Weitkamp (pp. 1-1).

Progress and future challenges in controlling automotive exhaust gas emissions by Martyn V. Twigg (pp. 2-15).

By the early 1970s increased use of cars in some major cities had resulted in serious concerns about urban air quality caused by engine exhaust gas emissions themselves, and by the more harmful species derived from them via photochemical reactions. The three main exhaust gas pollutants are hydrocarbons (including partially oxidised organic compounds), carbon monoxide and nitrogen oxides. Engine modifications alone were not sufficient to control them, and catalytic systems were introduced to do this. This catalytic chemistry involves activation of small pollutant molecules that is achieved particularly effectively over platinum group metal catalysts. Catalytic emissions control was introduced first in the form of platinum-based oxidation catalysts that lowered hydrocarbon and carbon monoxide emissions. Reduction of nitrogen oxides to nitrogen was initially done over a platinum/rhodium catalyst prior to oxidation, and subsequently simultaneous conversion of all three pollutants over a single three-way catalyst to harmless products became possible when the composition of the exhaust gas could be maintained close to the stoichiometric point. Today modern cars with three-way catalysts can achieve almost complete removal of all three exhaust pollutants over the life of the vehicle. There is now a high level of interest, especially in Europe, in improved fuel-efficient vehicles with reduced carbon dioxide emissions, and “lean-burn” engines, particularly diesels that can provide better fuel economy. Here oxidation of hydrocarbons and carbon monoxide is fairly straightforward, but direct reduction of NO_x under lean conditions is practically impossible. Two very different approaches are being developed for lean-NO_x control; these are NO_x-trapping with periodic reductive regeneration, and selective catalytic reduction (SCR) with ammonia or hydrocarbon. Good progress has been made in developing these technologies and they are gradually being introduced into production. Because of the nature of the diesel engine combustion process they produce more particulate matter (PM) or soot than gasoline engines, and this gives rise to health concerns. The exhaust temperature of heavy-duty diesels is high enough (250–400°C) for nitric oxide to be converted to nitrogen dioxide over an upstream platinum catalyst, and this smoothly oxidises retained soot in the filter. The exhaust temperature of passenger car diesels is too low for this to take place all the time, so trapped soot is periodically burnt in oxygen above 550°C. Here a platinum catalyst is used to oxidise higher than normal amounts of hydrocarbon and carbon monoxide upstream of the filter to give sufficient temperature for soot combustion to take place with oxygen. Diesel PM control is discussed in terms of a range of vehicle applications, including very recent results from actual on-road measurements involving a mobile laboratory, and the technical challenges associated with developing ultra-clean diesel-powered cars are discussed.

Keywords: Vehicle emissions; Autocatalysts; Three-way catalysts (TWCs); NO; _x; -traps; Selective catalytic reduction (SCR); Diesel particulate filters

Heat-integrated reactor concepts for catalytic reforming and automotive exhaust purification by Grigorios Kolios; Achim Gritsch; Arístides Morillo; Ute Tuttlies; Jens Bernnat; Frank Opferkuch; Gerhart Eigenberger (pp. 16-30).

Optimal solutions in environmental catalysis require a well-coordinated development of catalysts and of process design. This contribution is devoted to energy integrated design concepts for fuel reforming and for automotive exhaust purification. The examples presented demonstrate the importance of an innovative process design for optimal utilization of existing catalysts and show the potential of future developments.New concepts for steam reforming through the efficient coupling of the endothermic reforming reaction with an exothermic combustion reaction are discussed in the first part. These concepts have been implemented for methanol steam reforming in a counter-current reactor with distributed side feed of burner gas and for methane steam reforming in a modular reactor with a co-current reaction section for the endothermic and the combustion reaction and attached counter-current heat exchangers. Both applications employ the so-called folded sheet reactor design, which ensures an excellent heat transfer between the reforming and combustion channels and efficient heat recovery.A similar design solution is introduced for the apparently different case of automotive exhaust purification. The proposed concept aims at decoupling exhaust after-treatment from engine control. Its main component is a counter-current heat exchanger with integrated purification stages for HC-oxidation, NO_X storage and reduction and soot filtering. A small catalytic burner at the hot end of the heat exchanger provides both heat and oxidizing or reducing agents on demand. A new soot filter design allows for safe soot filter regeneration.

Keywords: Autothermal reactors; Heat-integrated reactors; Process integration; Steam reforming; Automotive exhaust purification; Diesel soot filtering

Prospects of N₂O emission regulations in the European fertilizer industry by Javier Pérez-Ramírez (pp. 31-35).

European authorities consider that N₂O emissions from nitric acid plants can be reduced to a large extent at a relatively low cost. Two regulation approaches can have major implications for the fertilizer industry in Europe. The EU integrated pollution prevention and control (IPPC) directive will be effective from October 2007 for existing plants. In this, emission permits will be based on best available techniques (BAT). Additionally, the EU commission will shortly consider whether the emission trading directive should be applicable to cover other greenhouse gases besides CO₂. This paper discusses advantages and drawbacks of these approaches, with emphasis on how emission trading with N₂O can be turned into a win–win situation both for European governments and for the fertilizer industry.

Keywords: N; ₂; O; Kyoto Protocol; Nitric acid production; Control technology; Catalysis; Regulations; IPPC directive; Emissions trading

An investigation of the thermal stability and sulphur tolerance of Ag/γ-Al₂O₃ catalysts for the SCR of NO_x with hydrocarbons and hydrogen by J.P. Breen; R. Burch; C. Hardacre; C.J. Hill; B. Krutzsch; B. Bandl-Konrad; E. Jobson; L. Cider; P.G. Blakeman; L.J. Peace; M.V. Twigg; M. Preis; M. Gottschling (pp. 36-44).

The sulphur tolerance and thermal stability of a 2wt% Ag/γ-Al₂O₃ catalyst was investigated for the H₂-promoted SCR of NO_x with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800°C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700°C, the deactivating effect of ageing was much less pronounced for the catalyst in the H₂-promoted octane-SCR reaction and ageing at 600°C resulted in an enhancement in activity for the reaction in the absence of H₂. For the toluene+H₂-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1ppm SO₂) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures (≤235°C), severe deactivation at intermediate temperatures (305 and 400°C) and activation of the catalyst at high temperatures (>500°C). The results can be explained by the activity of the catalyst for the oxidation of SO₂ to SO₃ and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen.

Keywords: SCR-NO; _x; Octane; Toluene; Silver; Ag/γ-Al; ₂; O; ₃; EXAFS; XRD; Sulphur tolerance; Ageing

Deactivation of a Fe-ZSM-5 catalyst during the selective catalytic reduction of NO by n-decane: An operando DRIFT study by Gérard Delahay; Ariel Guzmán-Vargas; Bernard Coq (pp. 45-52).

The selective catalytic reduction (SCR) of NO by n-decane was investigated on a Fe-ZSM-5 prepared by the FeCl₃ sublimation method. NO conversion profiles versus temperature were followed in both temperature programmed surface reaction (TPSR, 10°Cmin⁻¹) and steady state experiments. A higher NO conversion with a maximum of ca. 80% at 400°C is observed in the course of the TPSR tests. This phenomenon has been attributed to strong adsorption of n-decane which protects the active sites against the poisoning. Indeed, in steady state experiments at 390°C the strong decrease of activity as a function of time on stream is due to the polymerisation of conjugated nitriles. This study indicates that long chain alkanes are not the most adequate reductants of NO for high temperature SCR applications. Moreover, due to an easier polymerization of conjugated nitriles on iron zeolites (stronger Fe Lewis sites), this type of catalyst seems less attractive than Cu-zeolite catalysts for the SCR of NO by hydrocarbons in this respect.

Keywords: NO; _x; Selective catalytic reduction; n; -Decane; Iron; Zeolite; Deactivation

Kinetic experiments and modeling of NO oxidation and SCR of NO_x with decane over Cu- and Fe-MFI catalysts by Libor Čapek; Leonid Vradman; Petr Sazama; Moti Herskowitz; Blanka Wichterlová; Roie Zukerman; Roald Brosius; Johan A. Martens (pp. 53-57).

The kinetic model of the reduction of NO to N₂ with decane, developed based on the experimental data over Fe-MFI catalyst, has been applied for the oxidation of NO to NO₂ and reduction of NO₂ to N₂ with decane over Cu-MFI catalyst. The model fits well the experimental data of oxidation of NO as well as reduction of NO to N₂. Remarkable differences have been found in performance of Cu-MFI and Fe-MFI catalysts. While Fe-MFI is more active in oxidation of NO to NO₂, Cu-MFI exhibits much higher activity in the reduction of NO with decane. The kinetic model indicates that the significantly lower activity of Fe-MFI in comparison with Cu-MFI in transformation of NO_x to nitrogen is due to higher rate of transformation of NO₂, formed in the first step by the oxidation of NO, back to NO instead to molecular nitrogen.

Keywords: NO oxidation; NO; _x; reduction with hydrocarbons; Heterogeneous kinetics; Iron zeolite; Copper zeolite

Effect of rhodium on the properties of bifunctional M_xO_y/ZrO₂ catalysts in the reduction of nitrogen oxides by hydrocarbons by Tatyana V. Mironyuk; Svetlana N. Orlyk (pp. 58-64).

The catalytic properties of transition metal oxides (Cr, Ce, and Co) supported on ZrO₂ synthesized by various methods, as well as the effect of rhodium on the performance of the M_xO_y/ZrO₂ oxide systems in NO reduction with hydrocarbons (methane, propane–butane mixture, and propene) were studied. Scanning electron microscopy, ammonia thermoprogrammed desorption (NH₃-TPD), XPS, and IR spectroscopy were used to study the physicochemical indices of rhodium-promoted M_xO_y/ZrO₂ oxide catalysts. The enhancement of the redox properties of the oxide catalysts upon the introduction of rhodium does not alter their bifunctional nature in SCR activity: these catalysts have both redox and strong acid Brønsted-sites.

Keywords: Nitrogen oxides; Reduction; Hydrocarbons; Zirconia; Transition metal oxides; Rhodium; Acidity; Bifunctionality

Hydrogen as a remedy for the detrimental effect of aromatic and cyclic compounds on the HC-SCR over Ag/alumina by Kalle Arve; Henrik Backman; Fredrik Klingstedt; Kari Eränen; Dmitry Yu. Murzin (pp. 65-72).

The effect of hydrogen on the selective catalytic reduction of NO_x with n-octane, methylcyclohexane and toluene over a 2wt.% Ag/Al₂O₃ was investigated. Diesel fuels contain, in addition to straight hydrocarbons, varying amounts of cyclic and aromatic compounds, which have a detrimental effect on the Ag/Al₂O₃ catalyst activity. The results showed that the NO to N₂ conversion was significantly promoted, independent of the nature (straight, cyclic or aromatic) of the hydrocarbon, in the presence of 1vol.% H₂. The role of hydrogen is connected to a faster oxidation of the hydrocarbons and to enhanced formation of amines, which react with activated NO to form N₂.

Keywords: HC-SCR; Ag/alumina; NO; _x; reduction; Diesel; Aromatics; Hydrogen effect

Performance of solvothermally prepared Ga₂O₃-Al₂O₃ catalysts for SCR of NO with methane by Masaru Takahashi; Tetsu Nakatani; Shinji Iwamoto; Tsunenori Watanabe; Masashi Inoue (pp. 73-79).

The solvothermal reaction of mixtures of aluminum isopropoxide (AIP) and gallium acetylacetonate (Ga(acac)₃) directly yielded the mixed oxides of γ-Ga₂O₃-Al₂O₃. In the solvothermal synthesis, the crystal structure of mixed oxides was controlled by the initial formation of γ-Ga₂O₃ nuclei. The mixed oxides prepared in diethylenetriamine have extremely high activities for selective catalytic reduction (SCR) of NO with methane as a reducing agent. With increasing crystallite size of the spinel structure, the catalytic activity increased. The ratio of the amount of methane consumed by combustion to total methane conversion was proportional to the density of acid sites on the surface of the mixed oxides. The mixed oxide catalysts prepared in diethylenetriamine had lower densities of acid sites and showed a higher methane-efficiency for CH₄-SCR than those prepared in other solvents. These catalysts maintained their high activity even when the reaction was carried out under the severe conditions (i.e., high space velocity and low NO concentration).

Keywords: Ga; ₂; O; ₃; -Al; ₂; O; ₃; mixed oxide; Solvothermal method; Selective catalytic reduction; NO; Methane

Reactivity of NO/NO₂–NH₃ SCR system for diesel exhaust aftertreatment: Identification of the reaction network as a function of temperature and NO₂ feed content by Cristian Ciardelli; Isabella Nova; Enrico Tronconi; Daniel Chatterjee; Brigitte Bandl-Konrad; Michel Weibel; Bernd Krutzsch (pp. 80-90).

We present a systematic study of the NH₃-SCR reactivity over a commercial V₂O₅–WO₃/TiO₂ catalyst in a wide range of temperatures and NO/NO₂ feed ratios, which cover (and exceed) those of interest for industrial applications to the aftertreatment of exhaust gases from diesel vehicles. The experiments confirm that the best deNO_x efficiency is achieved with a 1/1 NO/NO₂ feed ratio. The main reactions prevailing at the different operating conditions have been identified, and an overall reaction scheme is herein proposed.Particular attention has been paid to the role of ammonium nitrate, which forms rapidly at low temperatures and with excess NO₂, determining a lower N₂ selectivity of the deNO_x process. Data are presented which show that the chemistry of the NO/NO₂–NH₃ reacting system can be fully interpreted according to a mechanism which involves: (i) dimerization/disproportion of NO₂ and reaction with NH₃ and water to give ammonium nitrite and ammonium nitrate; (ii) reduction of ammonium nitrate by NO to ammonium nitrite; (iii) decomposition of ammonium nitrite to nitrogen. Such a scheme explains the peculiar deNO_x reactivity at low temperature in the presence of NO₂, the optimal stoichiometry (NO/NO₂=1/1), and the observed selectivities to all the major N-containing products (N₂, NH₄NO₃, HNO₃, N₂O). It also provides the basis for the development of a mechanistic kinetic model of the NO/NO₂–NH₃ SCR reacting system.

Keywords: Aftertreatment; Diesel-urea SCR; deNO; _x; Fast SCR; Ammonium nitrate; Transient response; Dynamic methods

Surface chemistry and kinetics of the hydrolysis of isocyanic acid on anatase by Philipp Hauck; Andreas Jentys; Johannes A. Lercher (pp. 91-99).

In order to meet the stricter NO_x and particulate emission limits for commercial vehicles, the selective catalytic reduction (SCR) with urea is currently seen having the highest potential. The conversion of urea into ammonia and carbon dioxide consists of two consecutive reactions, in which isocyanic acid is an intermediate that is hydrolyzed over TiO₂. The intrinsic kinetics and the surface chemistry for this reaction are explored. Up to a temperature of 132°C the reaction was in the intrinsic kinetic regime ( E_A=73kJ/mol), while at higher temperatures the reaction was limited by pore and external diffusion constraints, respectively. In the presence of NO, NH₃ and NO₂, the catalytic activity was negatively influenced, increasing in severity in the sequence mentioned indicating that nitrates formed from NO₂ were most effective in blocking cations and anions of TiO₂. IR spectroscopy indicates that dissociative adsorption of HNCO on TiO₂ forms Ti–NCO and hydrogen bonded OH species. In the presence of water, isocyanic acid was so rapidly hydrolyzed that only adsorbed ammonia was observed on the catalyst surface. The presence of NO, NH₃ and NO₂ retards hydrolysis leading to the appearance of isocyanate species on the surface.

Keywords: Diesel emission; SCR; DeNO; _x; Urea; Hydrolysis; Isocyanic acid; Isocyanate; Adsorption; Inhibition; TiO; ₂

Kinetics of the NO+H₂ reaction over supported noble metal based catalysts: Support effect on their adsorption properties by Fabien Dhainaut; Stan Pietrzyk; Pascal Granger (pp. 100-110).

This paper reports a kinetic investigation of the global reduction of NO by H₂ which has been considered as a probe reaction for characterising the adsorption properties of supported palladium based catalysts. A particular attention has been paid towards the influence of the support on the catalytic properties of Pd, particularly towards the production of undesirable by-products such as nitrous oxide (N₂O) and ammonia (NH₃). It has been found that the kinetics of the overall NO+H₂ reaction on Pd/Al₂O₃ can be correctly depicted according to a Langmuir–Hinshelwood mechanism involving the dissociation of nitrosyl species assisted by chemisorbed hydrogen atoms. On the other hand, Pd/LaCoO₃ exhibits a different kinetic behaviour towards the adsorption of hydrogen depending on the pre-activation thermal treatment. In that case, different mechanisms may occur.

Keywords: Palladium based catalysts; NO; +; H; ₂; reaction; Hydrogen; N; ₂; O selectivity; NH; ₃; selectivity

Mechanistic insights into the formation of N₂O and N₂ in NO reduction by NH₃ over a polycrystalline platinum catalyst by Vita A. Kondratenko; Manfred Baerns (pp. 111-118).

The reaction pathways of N₂ and N₂O formation in the direct decomposition and reduction of NO by NH₃ were investigated over a polycrystalline Pt catalyst between 323 and 973K by transient experiments using the temporal analysis of products (TAP-2) reactor. The interaction between nitric oxide and ammonia was studied in the sequential pulse mode applying¹⁵NO. Differently labelled nitrogen and nitrous oxide molecules were detected. In both, direct NO decomposition and NH₃–NO interaction, N₂O formation was most marked between 573 and 673K, whereas N₂ formation dominated at higher temperatures. An unusual interruption of nitrogen formation in the¹⁵NO pulse at 473K was caused by an inhibiting effect of adsorbed NO species. The detailed analysis of the product distribution at this temperature clearly indicates different reaction pathways leading to the product formation. Nitrogen formation occurs via recombination of nitrogen atoms formed by dissociation of nitric oxide or/and complete dehydrogenation of ammonia. N₂O is formed via recombination of adsorbed NO molecules. Additionally, both products are formed via interactions between adsorbed ammonia fragments and nitric oxide.

Keywords: Mechanism; NO decomposition; NO reduction by NH; ₃; N; ₂; O formation; ¹⁵; NO; Pt gauze; Transient experiments; TAP reactor

Modeling and simulation of the injection of urea-water-solution for automotive SCR DeNO_x-systems by Felix Birkhold; Ulrich Meingast; Peter Wassermann; Olaf Deutschmann (pp. 119-127).

The evaporation of water from a single droplet of urea water solution is investigated theoretically by a Rapid Mixing model and a Diffusion Limit model, which also considers droplet motion and variable properties of the solution. The Rapid Mixing model is then implemented into the commercial CFD code Fire 8.3 from AVL Corp. Therein, the urea water droplets are treated with Lagrangian particle tracking. The evaporation model is extended for droplet boiling and thermal decomposition of urea. CFD simulations of a SCR DeNO x-system are compared to experimental data to determine the kinetic parameters of the urea decomposition. The numerical model allows to simulate SCR exhaust system configurations to predict conversion and local distribution of the reducing agent.

Keywords: Evaporation; Thermal decomposition; Urea-water-solution; Simulation; Injection; CFD; SCR; NO; _x

Design of catalysts for deNO_x process using synergistic phenomenon by T.N. Burdeinaya; V.A. Matyshak; V.F. Tret’yakov; L.S. Glebov; A.G. Zakirova; M.A. Carvajal Garcia; M.E. Arias Villanueva (pp. 128-137).

Investigation of the mechanism of the selective reduction of NO_x by propane over the individual samples of commercial catalysts NTK, STK, and Ni–Cr-oxide catalyst and over their binary mechanical mixtures has shown that the synergistic effect observed in the latter case is caused by the oxidative activation of propane on the STK and Ni–Cr-oxide surface which results in the formation of more effective reducing agents, propylene and hydrogen correspondingly. In the case of the Ni–Cr-oxide and NTK catalytic system, hydrogen forms over the former catalyst in propane oxidation, migrates through the gas phase to the latter catalyst, where NO_x is activated with the formation of nitrate structures which interact with the said hydrogen giving the products of the overall reaction, N₂ and H₂O. When the pair of NTK and STK is concerned, the interaction of C₃H₈ and O₂ over the latter catalyst gives stable products of partial propane oxidation and/or oxidative dehydrogenation which are transported due to interphase diffusion to NTK surface. The nature of observed synergistic enhancement of catalysis in the case of binary mixtures is proposed under the terms of “remote control” mechanism described in literature and can serve a useful purpose in the design of catalysts for this reaction.

Keywords: Selective reduction of nitrogen oxides; The reaction mechanism; Mechanical mixture of oxide catalysts; Synergy

A combination of Ag/alumina and Ag modified ZSM-5 to remove NO_x and CO during lean conditions by P. Konova; K. Arve; F. Klingstedt; P. Nikolov; A. Naydenov; N. Kumar; D. Yu. Murzin (pp. 138-145).

Single and bi-metallic silver modified ZSM-5 catalysts were synthesized using different methods of preparation, characterized by several techniques and tested in simulated diesel conditions. Additionally the catalytic behaviour of the most active catalyst, containing 5wt.% Ag and prepared by impregnation (5Ag(Imp)-H-ZSM-5), was studied over a broad temperature range with two reducing agents (octane and propene). To correlate the catalytic activity of the prepared catalysts with preparation parameters the materials were characterized by XRD, SEM, N₂-physisorption, octane/propene-TPD, EPR and ICP techniques. A dual bed system consisting of Ag/alumina and the most active zeolitic material (5Ag(Imp)-H-ZSM-5) was shown not only to substantially enhance the activity of Ag/alumina in the low temperature region, but also to completely oxidize the CO and unburned hydrocarbons.

Keywords: Ag/ZSM-5; Ag/alumina; HC-SCR; NO; _x; emissions; Dual bed

Direct decomposition of nitric oxide over Ba catalysts supported on CeO₂-based mixed oxides by Shinji Iwamoto; Ryosuke Takahashi; Masashi Inoue (pp. 146-150).

The direct decomposition of nitric oxide (NO) over barium catalysts supported on various metal oxides was examined in the absence and presence of O₂. Among the Ba catalysts supported on single-component metal oxides, Ba/Co₃O₄ and Ba/CeO₂ showed high NO decomposition activities, while Ba/Al₂O₃, Ba/SiO₂, and Ba/TiO₂ exhibited quite low activities. The effect of an addition of second components to Co and Ce oxides was further examined, and it was found that the activities were significantly enhanced using Ce–Mn mixed oxides as support materials. XRD results indicated the formation of CeO₂–MnO_x solid solutions with the cubic fluorite structure. O₂-TPD of the CeO₂–MnO_x solid solutions showed a large desorption peak in a range of relatively low temperature. The BET surface areas of the CeO₂–MnO_x solid solutions were larger than those of pure CeO₂ and Mn₂O₃. These effects caused by the addition of Mn are responsible for the enhanced activities of the Ba catalysts supported on Ce–Mn mixed oxides.

Keywords: NO decomposition; Barium catalyst; Ce–Mn oxide; Solid solution

Multifunctional catalysts for de-NO_x processes: The case of H₃PW₁₂O₄₀·6H₂O-metal supported on mixed oxides by Miguel Angel Gómez-García; Véronique Pitchon; Alain Kiennemann (pp. 151-159).

The role of a multifunctional catalyst for de-NO_x process has been investigated. The NO_x storage capacity of H₃PW₁₂O₄₀·6H₂O (HPW) was improved by the presence of a noble metal (Pt, Rh or Pd). Both HPW and noble metal were deposited on a specific support (based on Zr–Ce or Zr–Ti). The presence of noble metal in several oxidation states, as evidenced by TPR and IR, involves the possibility of forming different catalytic sites: (i) M⁰ (zero-valent metal) and perhaps (ii) (metal–H) δ⁺ from specific interactions between noble metal and the HPW proton. Supports were also able to adsorb and activate NO_x and to generate cationic catalytic sites (M x⁺). These cationic sites seem to be the clue for their important activity toward NO_x reduction. This catalyst presents an outstanding resistance to SO₂ poisoning which can be related to NO and NO₂ absorption mechanism in HPW. The use of alternating short cycles of lean/rich mixtures allows us optimising the performance of this catalytic system in terms of both NO_x reduction capacity and NO_x storage efficiency: up to 48 and 84%, respectively (with a 2% CO+1% H₂ mixture for reducing). Experimental results sustain two hypotheses: first, HPW-metal-support catalyst includes several (independent) catalytic functions required for a de-NO_x process to occur and second, the formation of oxygenate active species must be indispensable for NO_x reduction into nitrogen.

Keywords: de-NO; _x; process; HPW; Noble metal; Cerium; Zirconium and titanium mixed oxides; NSR technique; NO; _x; reduction mechanism

Response surface study of the performance of lean NO_x storage catalysts as a function of reaction conditions and catalyst composition by Reed J. Hendershot; Rohit Vijay; Christopher M. Snively; Jochen Lauterbach (pp. 160-171).

NO_x storage and reduction (NSR) catalysts containing Pt, Ba and Fe were studied as a function of reaction conditions and catalyst composition using response surface methodology combined with high-throughput experimentation. The concentrations of the reactant gases and the reactor temperature were varied to probe their effect on catalyst performance, as quantified by lean NO_x storage and N₂O production. An empirical model relating the catalyst performance to five reaction condition variables and three metal weight loading variables has also been developed. It was found that the temperature and the concentrations of the reducing agents, i.e. carbon monoxide and ethylene, had the strongest effect on the lean NO_x storage. It was also found that the Pt and Ba weight loadings had a much greater effect than Fe weight loadings on the performance of NSR catalysts. This model provides insight about the factors controlling the NO_x conversion by NSR catalysts and also predicts the optimum catalyst composition for given reaction conditions and vice versa. As an additional study, the relationship between sulfur poisoning, nitrous oxide production, and exotherm generation was also explored.

Keywords: NO; _x; storage and reduction; NO; _x; trap; Nitrous oxide; Sulfur poisoning; High-throughput experimentation; Combinatorial catalysis; Design of experiments; Response surface design

Performances of SO_x traps derived from Cu/Al hydrotalcite for the protection of NO_x traps from the deactivation by sulphur by Gabriele Centi; Siglinda Perathoner (pp. 172-178).

The behavior of Cu/Al mixed oxides (Cu/Al ratio in the 1:2–1:5 range) have been studied as novel, noble-metal free SO_x traps to protect NO_x traps from the deactivation by sulphur. The investigation was made both in a thermobalance apparatus and in a flow reactor, the latter simulating the reaction conditions and space-velocities of exhaust gases from lean-burn or diesel engines. The analysis of the SO₂ uptake curves as a function of the Cu/Al ratio and reaction temperature indicates that the reaction mechanism of SO₂ uptake depends on two reversible surface processes (the chemisorption of SO₂ and its oxidation by copper ions) and a nearly irreversible process (bulk diffusion of the sulphate species). The rate of these processes depends on (i) the Cu/Al ratio and nature of the surface copper species, (ii) the surface area of the catalyst, (iii) the reaction conditions, and (iv) the degree of sulphation. The SO_x traps showing the best performances in thermogravimetric tests were found also to show the best behavior in flow reactor tests, confirming the validity of thermogravimetric tests, notwithstanding the different composition of the feed used. The SO_x trap having a Cu/Al ratio of 1:2 shows better performances with respect to a reference “state-of-the-art” SO_x trap containing 2% Pt.

Keywords: SO; ₂; SO; _x; trap; Copper; Hydrotalcite; Cu/Al mixed oxides

Kinetic modelling of sulfur deactivation of Pt/BaO/Al₂O₃ and BaO/Al₂O₃ NO_x storage catalysts by Jazaer Dawody; Magnus Skoglundh; Louise Olsson; Erik Fridell (pp. 179-188).

In this work, a kinetic model is constructed to simulate sulfur deactivation of the NO_x storage performance of BaO/Al₂O₃ and Pt/BaO/Al₂O₃ catalysts. The model is based on a previous model for NO_x storage under sulfur-free conditions. In the present model the storage of NO_x is allowed on two storage sites, one for complete NO_x uptake and one for a slower NO_x sorption. The adsorption of SO_x is allowed on both of these NO_x storage sites and on one additional site which represent bulk storage. The present model is built-up of six sub-models: (i) NO_x storage under sulfur-free conditions; (ii) SO₂ storage on NO_x storage sites; (iii) SO₂ oxidation; (iv) SO₃ storage on bulk sites; (v) SO₂ interaction with platinum in the presence of H₂; (vi) oxidation of accumulated sulfur compounds on platinum by NO₂. Data from flow reactor experiments are used in the implementation of the model. The model is tested for simulation of experiments for NO_x storage before exposure to sulfur and after pre-treatments either with SO₂+O₂ or SO₂+H₂. The simulations show that the model is able to describe the main features observed experimentally.

Keywords: Sulfur deactivation; NO; _x; storage; Kinetic modelling; Pt; BaO; Al; ₂; O; ₃

New insight into the interaction of sulfur with diesel NO_x storage catalysts by F. Rohr; U. Göbel; P. Kattwinkel; T. Kreuzer; W. Müller; S. Philipp; P. Gélin (pp. 189-197).

A commercial NO_x-storage catalyst (NSC) has been subjected to different aging procedures on the engine bench simulating 100,000km mileage. The aging consisted of cyclical sulfur exposure, subsequent sulfur removal and testing of the catalytic activity. More aggressive desulfation procedures result in more efficient sulfur removal and consequently good high temperature NO_x-conversion. However, low temperature NO_x-performance is lower than for agings employing more moderate desulfation conditions.Sulfur post mortem analyses reveal a slight decrease of residual sulfur concentration over the length of all catalysts after completion of the aging. BET and CO-chemisorption data are in line with the increase of temperature from catalyst inlet to outlet during the desulfation. The conversion of BaCO₃ to BaSO₄ during the sulfur poisoning was followed by IR, TPD and TPR. A quantitative analysis of the data shows that at the end of the agings all residual sulfur is mainly located at barium sites as opposed to other oxide components like e.g. alumina or ceria. TPR data suggest that prolonged rich purges of the sulfated catalyst lead to an efficient decomposition of sulfates however some sulfur is being trapped in the form of BaS which seems difficult to remove under constant rich conditions.XPS data suggest that the bulk sulfur amounts in the catalyst may be decoupled from the actual concentration at the catalyst surface. In that sense, the residual sulfur concentration might be limited in some cases as a criterion to assess the performance of a NSC. More reducing desulfation conditions cause the residual sulfur to be present in the form of more reduced sulfur species (sulfites, sulfides) on the catalyst.

Keywords: NO; _x; storage; Sulfur; Sulfur poisoning

The low-temperature performance of NO_x storage and reduction catalyst by Naoki Takahashi; Kiyoshi Yamazaki; Hideo Sobukawa; Hirofumi Shinjoh (pp. 198-204).

The catalytic performance and the behavior of NO_x storage and reduction (NSR) over a model catalyst for lean-burn gasoline engines have been mainly investigated and be discussed based on the temperature and reducing agents use in this study. The experimental results have shown that the NO_x storage amount in the lean atmosphere was the same as the NO_x reduction amount from the subsequent rich spike (RS) above the temperature of 400°C, while the former was greater than the latter below the temperature of 400°C. This indicated that when the temperature was below 400°C compared with the NO_x storage stage, the reduction of the stored NO_x is somehow restricted. We found that the reduction efficiencies with the reducing agents decrease in the order H₂>CO>C₃H₆ below 400°C, thus not all of the NO_x storage sites could be fully regenerated even using an excessive reducing agent of CO or C₃H₆, which was supplied to the NSR catalyst, while all the NO_x storage sites could be fully regenerated if an adequate amount of H₂ was supplied. We also verified that the H₂ generation more favorably occurred through the water gas shift reaction than through the steam reforming reaction. This difference in the H₂ generation could reasonably explain why CO was more efficient for the reduction of the stored NO_x than C₃H₆, and hinted as a promising approach to enhance the low-temperature performance of the current NSR catalysts though promoting the H₂ generation reaction.

Keywords: Lean-burn engines; NO; _x; storage and reduction catalyst; H; ₂; Water gas shift reaction; Steam reforming reaction

A combination of NO_x trapping materials and urea-SCR catalysts for use in the removal of NO_x from mobile diesel engines by James A. Sullivan; Orla Keane (pp. 205-214).

Preliminary studies on a series of nanocomposite BaO–Fe ZSM-5 materials have been carried out to determine the feasibility of combining NO_x trapping and SCR-NH₃ reactions to develop a system that might be applicable to reducing NO_x emissions from diesel-powered vehicles. The materials are analysed for SCR-NH₃ and SCR-urea reactivity, their NO_x trapping and NH₃ trapping capacities are probed using temperature programmed desorption (TPD) and the activities of the catalysts for promoting the NH_{3 ads}+NO/O₂→N₂ and NO x_ads+NH₃→N₂ reactions are studied using temperature programmed surface reaction (TPSR).

Keywords: NO; _x; NH; ₃; SCR; Urea; BaO

Development of a dosing strategy for a heavy-duty diesel exhaust cleaning system based on NO_X storage and reduction technology by Design of Experiments by K. Papadakis; C.U.I. Odenbrand; J. Sjöblom; D. Creaser (pp. 215-225).

A dosing strategy for the transient control of an exhaust after-treatment system using the NO_X storage and reduction approach was developed on a heavy-duty diesel engine rig equipped with an 11l diesel engine. The catalysts were oxidation catalysts of 8.4l and NO_X storage and reduction catalysts of 16.8l total volume. The dosing strategy has been tested in a European Transient Cycle (ETC) resulting in a NO_X reduction of 60% (by 4.5g/kWh) with a fuel penalty of 6.6% when the catalysts were preconditioned to 450°C. The reducing agent was diesel fuel. To keep the fuel penalty low, a bypass system was used which bypassed approximately 90% of the exhaust flow under the regeneration periods. The parameters for the dosing strategy were obtained from steady-state optimization experiments (constant speed and torque) using Design of Experiments (DoE) to obtain much information from few experiments. The system was optimized for a high degree of NO_X reduction with a low fuel penalty. The period when the flow through the catalyst is reduced (bypass time), the cycle time, the injection time and rate are important parameters to achieve an improved NO_X reduction. The optimal values of these parameters varied with the load points used. The steady-state NO_X conversion was approximately 60% (3.3–4.1g/kWh) at catalyst temperatures between 330 and 530°C. The most promising parameters for a large NO_X reduction and a low fuel penalty have been applied in the dosing strategy and tested in an ETC.

Keywords: Experimental design; Design of experiments; DoE; NO; _X; storage and reduction; NSR; Injection parameters; Fuel penalty; Bypass; System optimization; Dosing strategy

NO_x storage/reduction over lean-burn automotive catalysts by C.M.L. Scholz; V.R. Gangwal; J.H.B.J. Hoebink; J.C. Schouten www.chem.tue.nl/scr (pp. 226-232).

This paper shows the behavior of a Pt/Ba/γ–Al₂O₃ automotive catalyst in a fixed bed reactor during cyclic operation at lean and rich gas phase conditions at short (seconds) and long (hours) cycling times at different temperatures. Reactor exit gas phase concentrations have been measured and catalyst properties have been determined before and after selective cycling experiments. The experimental results indicate that: (i) Upon 9h lean and 15h rich cycling, the NO oxidation efficiency of the catalyst decreases with time while incomplete regeneration is seen, even after 15h rich exposure with H₂. The cyclic steady state is reached after 3lean/rich cycles, at which only 60% of the available barium is involved in the NO_x storage/reduction. (ii) The BET surface area, pore volume, and Pt dispersion decrease by approximately 40%, which may be a result of masking of Pt sites or blocking of pores of the barium clusters as BaCO₃ becomes Ba(NO₃)₂. Experiments with catalyst pellet sizes of 180 and 280μm along with XPS measurements show that blocking of catalyst pellet pores is not taking place. (iii) When applying lean/rich cycling in the order of seconds, it appears that catalyst history and lean/rich timing affect the number of cycles required to arrive at a closed N balance. XRD results after lean exposure confirm the formation of barium nitrate in the bulk of the barium cluster.

Keywords: NO; _x; trap; Barium nitrate; Lean-burn; NO; _x; storage; NO; _x; reduction; Hydrogen

Wall-flow filters with wall-integrated oxidation catalyst: A simulation study by Martin Votsmeier; Jürgen Gieshoff; Markus Kögel; Markus Pfeifer; Jens Felix Knoth; Alfons Drochner; Herbert Vogel (pp. 233-240).

Diesel soot abatement via diesel particulate filters composed of so-called wall-flow monoliths is well established. Today, due to recent improvements in the production technology full-featured catalyst functionality can be implemented in the filter walls.This work focuses on a comparison of the reactor performance of the wall-flow filter and the conventional flow-through monolith. To this end a two-dimensional numerical model is set up for each of the two reactor configurations.Concentration profiles in the wall-flow filter systematically change as a function of flow velocity.At high flow velocities transport from the inlet channel into the porous wall is nearly entirely dominated by convection. This leads to uniform axial concentration profiles in the inlet and outlet channel and a steep gradient in the porous wall.At low velocities radial transport into the porous wall is dominated by diffusive transport. This leads to a negligible radial concentration gradient between the inlet and the outlet channel.Under most operating conditions relevant for an automotive exhaust catalyst the flow velocity is in an intermediate range with contributions of diffusive and convective transport.The transition from entirely convection dominated transport at high space velocities to increasingly diffusion dominated transport at lower flow velocities is similarly found for first order kinetics and a generalized Langmuir–Hinshelwood–Hougen–Watson (LHHW) rate law.Wall-flow filters show systematic conversion advantages over the conventional monolith for a first order reaction. For a reaction with LHHW-type kinetics this effect is not generally observed. It is one major result of this work that the relative performance of the two reactor configurations depends on the kinetics of the catalyzed reaction.

Keywords: Wall-flow monolith; Diesel particulate filter; Fluid dynamic; Simulation; Modeling; Monolith

Mapping of diesel soot regeneration behaviour in catalysed silicon carbide filters by Marco Federico Pidria; Flavio Parussa; Edoardo Merlone Borla (pp. 241-246).

A range of different soot regeneration conditions has been explored using laboratory scale catalysed soot filters, loaded on a state-of-the-art common rail diesel engine. The concurrent effect of oxygen feed rate (manageable both by flow rate and by oxygen concentration) and of heat removal, strictly linked to exhaust flow rate and temperature, was investigated. It has been observed that oxygen plays a major role in defining the oxidising reaction rate and determining possibly dangerous thermal peaks. Nevertheless, especially at high flow rate, the heat removal capability of the gas flow significantly increases the differences between the reaction behaviour at different oxygen contents.

Keywords: Emission control devices; Catalysed particulate filters; Particulate regeneration

Copper-vanadium-cerium oxide catalysts for carbon black oxidation by R. Cousin; S. Capelle; E. Abi-Aad; D. Courcot; A. Aboukaïs (pp. 247-253).

Series of V-Ce and Cu-V-Ce oxides with different atomic ratios were prepared by the incipient wetness impregnation of a ceria support. These solids were studied by TG–DTA in the oxidation of a model soot (carbon black (CB) Degussa N330). V-Ce oxides are active in the carbon black oxidation and an increase in the vanadium content enhances their catalytic activity. This observation is correlated with the presence of a V₂O₅ phase. However, this catalytic system (V-Ce) produces CO during the CB oxidation. Adding copper to the V-Ce oxide to form a ternary system (Cu-V-Ce) has a beneficial effect on the CO₂ selectivity. A synergistic effect between copper and vanadium species on ceria is evidenced. The presence of the V₂O₅ phase on the catalyst enhances the activity for the CB oxidation while copper (II) species decrease the CO production significantly.

Keywords: Ceria; Carbon black; V-Ce oxide; Cu-V-Ce oxide; V; ₂; O; ₅; CeVO; ₄; TG–DTA

Microwave improvement of catalyst performance in soot oxidation without additives by Vincenzo Palma; Paola Russo; Giuseppa Matarazzo; Paolo Ciambelli (pp. 254-260).

The application of microwaves allows to overcome technical hitches related to the regeneration of soot-filters allowing to perform it independently on the engine operating conditions. The performance of a SiC foam filter during microwave regeneration was investigated with and without a catalyst coating. The regeneration efficiency and the energy required for regeneration were evaluated for catalytic and uncatalytic SiC foams by varying the operating conditions of soot trapping.Results showed that for both catalytic foams, Fe/V/K and Cu/V/K, the capability to be heated independently of the amount of soot allows to maintain temperature sufficiently high to perform a complete foam filter regeneration. Moreover, the microwave absorbing properties of the catalytic phases allow to perform regeneration with a lower energy consumption with respect to the uncatalytic case. The presence of a catalyst also allows to overcome the dependence of microwave-assisted regeneration process on the operating conditions of soot loading.

Keywords: Microwave; Soot; Foam; Filter; Catalyst

Potassium–copper and potassium–cobalt catalysts supported on alumina for simultaneous NO_x and soot removal from simulated diesel engine exhaust by N. Nejar; M.J. Illán-Gómez (pp. 261-268).

This paper deals with the activity of bimetallic potassium–copper and potassium–cobalt catalysts supported on alumina for the reduction of NO_x with soot from simulated diesel engine exhaust. The effect of the reaction temperature, the soot/catalyst mass ratio and the presence of C₃H₆ has been studied. In addition, the behavior of two monometallic catalysts supported on zeolite beta (Co/beta and Cu/beta), previously used for NO_x reduction with C₃H₆, as well as a highly active HC-SCR catalyst (Pt/beta) has been tested for comparison. The preliminary results obtained in the absence of C₃H₆ indicate that, at temperatures between 250 and 400°C, the use of bimetallic potassium catalysts notably increases the rate of NO_x reduction with soot evolving N₂ and CO₂ as main reaction products. At higher temperatures, the catalysts mainly favor the direct soot combustion with oxygen. In the presence of C₃H₆, an increase in the activity for NO_x reduction has been observed for the catalyst with the highest metal content. At 450°C, the copper-based catalysts (Cu/beta and KCu2/Al₂O₃) show the highest activity for both NO_x reduction (to N₂ and CO₂) and soot consumption. The Pt/beta catalyst does not combine, at any temperature, a high NO_x reduction with a high soot consumption rate.

Keywords: Diesel; Soot; NO; _x; C; ₃; H; ₆; Bimetallic; Pt; K; Cu; Co

Analysis of a kinetic model describing the dynamic operation of a three-way catalyst by R. Möller; C.H. Onder; L. Guzzella; M. Votsmeier; J. Gieshoff (pp. 269-275).

Simulation models of three-way catalysts (TWC) are very useful for the design and tests of catalyst controllers. When applying such models to controller design, accurate descriptions of the emissions restricted by legislation and of the emissions driving the λ sensor (NO_x, CO, HC, H₂ and O₂) are important. A kinetic one-channel model of a TWC, capable of calculating the demanded output, was recently published. That model was developed based on measurements from an engine test bench. Since, the dynamic behaviour of the catalyst is very complex and the variation of the exhaust gas composition is very limited on an engine test bench, various phenomena can hardly be analysed separately on an engine test bench. This fact led to the choice of the model-gas test bench, which allows the study of the individual phenomena under idealised conditions.This contribution now is to validate that model using measurement results obtained on a model-gas test bench. To analyse the performance of the TWC model, the response of the TWC to a defined input is measured under various conditions and compared with results of simulations. The main goals of this investigation include the analysis of dynamic effects, such as the deactivation of the catalyst under rich conditions, the role of water and hydrogen (water–gas shift reaction), and the storage of components other than oxygen.

Keywords: H; ₂; -to-CO ratio; Water–gas shift

Three-way-catalyst induced benzene formation: A precursor study by Stefan Bruehlmann; Philippe Novak; Peter Lienemann; Matthias Trottmann; Urs Gfeller; Christoph N. Zwicky; Bastian Bommer; Hugo Huber; Max Wolfensberger; Norbert V. Heeb (pp. 276-283).

The implementation of the three-way-catalyst technology was the major step for pollutant abatement of gasoline vehicles. There are, however, situations, where the engine has to be operated at sub-stoichiometric combustion. At such fuel-rich conditions, an intense formation of benzene was observed over a Pd/Rh-based three-way-catalyst (TWC), when operating the catalyst in a critical temperature window of 600–730°C. At least four different reaction pathways can lead to benzene formation on the catalyst, viz. (i) dealkylation of alkylbenzenes under steam reforming conditions, (ii) hydrodealkylation, (iii) aromatization of cyclohexanes, and (iv) cyclotrimerization of ethyne. Based on the engine-out exhaust composition only routes (i) and (ii) seem to be reasonable. The pre-catalyst application of 12 different alkylbenzenes indeed revealed that benzene formation is possible from all these precursors. At most up to 60% of the spiked precursors were converted to benzene. For meta- and para-substituted alkylbenzenes, a multi-step mechanism is proposed because partial dealkylation products such as toluene were formed as well. But a different, one-step mechanism is assumed for ortho-substituted alkylbenzenes, since no intermediates could be detected. No C–C-bond cleavage was observed within alkyl side chains. It is concluded that dealkylation reactions of alkylbenzenes are the major pathways leading to benzene formation in the TWC. Because fuel-rich combustion conditions have to be applied for the regeneration of deNO_X traps or certain particulate traps as well, this chemistry might also be of relevance for these exhaust gas treatment systems.

Keywords: Secondary emissions; Dealkylation of alkylbenzenes; Benzene and toluene formation window; Chemical ionization mass spectrometry

The oxidizing role of CO₂ at mild temperature on ceria-based catalysts by O. Demoulin; M. Navez; J.-L. Mugabo; P. Ruiz (pp. 284-293).

For thermodynamic reasons, CO₂ has always been considered as inert at mild reaction temperatures (∼300°C). In this study, we show that CO₂ may be used as a valuable compound for the catalytic combustion of methane (CCM), if ceria-based materials are used as support for the palladium active phase. Adding CO₂ in the feed significantly improves performances of ceria-zirconia supported catalysts. On the contrary, catalytic performances are inhibited on Pd/γ-Al₂O₃. Inhibition can be avoided by mixing the Pd/γ-Al₂O₃ catalyst with some CeO₂ evidencing cooperation phenomena between both catalysts. In situ DRIFTS experiments show that the inhibition of the alumina-supported catalyst is not due to formation of carbonates species. After an in situ reducing pre-treatment, pure CO₂ is able to rapidly oxidize reduced Pd/Ce_0.21Zr_0.79O₂ catalyst at 300°C. Dissociation of CO₂ on Ce_0.21Zr_0.79O₂ would be responsible for the oxidation process. Thus, CO₂ helps in replenishing the O reservoir (OSC) of the Ce-Zr-O support which is normally consumed by reductants such as CH₄, H₂ or other HC's. XPS experiments show enrichment in oxygen species bound to Ce (Low BE O1s) on the surface of ceria-zirconia when working in the presence of CO₂. Implications of these results on the behavior of ceria-containing catalysts can be important for practical applications, e.g., in automotive exhaust catalysis.

Keywords: Methane oxidation; Combustion; Ceria; Palladium; CO; ₂; XPS; In situ DRIFTS

Millisecond step-scan FT-IR transmission spectroscopy under transient reaction conditions: CO oxidation over Pt/Al₂O₃ by Ansgar Wille; Erik Fridell (pp. 294-304).

Time-resolved FT-IR spectra of CO oxidation over Pt/Al₂O₃ catalysts were collected in situ in transmission mode under transient reaction conditions. Using the step-scan acquisition mode of a commercial FT-IR spectrometer, time-resolution of a few milliseconds, compared to several hundred milliseconds in the normal rapid-scan mode, could be achieved. The experiments were triggered by reproducible oxygen gas pulses at constant temperature. Infrared light transmission, uniform heating and fast gas exchange were realized by pressing the pure catalyst powder onto a thin stainless steel wire mesh using a low volume reaction cell. By comparing the results of both acquisition modes, rapid-scan and step-scan, we will demonstrate, that it is possible, in a rather simple way, to investigate heterogeneously catalysed reactions under reaction conditions by means of FT-IR spectroscopy with time-resolutions down to a few milliseconds, and, in principle, lower. CO oxidation between 443 and 573K over 1%Pt/γ-Al₂O₃ and 4%Pt/γ-Al₂O₃ catalysts has been investigated as a test reaction. By using the high time-resolution of the step-scan acquisition mode we could obtain new details of the dynamics of the CO oxidation reaction over a supported Pt catalyst at high temperatures and 1atm pressure.

Keywords: Time-resolved FTIR; Step-scan; CO oxidation; Platinum; Transient reaction

On the use of mechanistic CO oxidation models with a platinum monolith catalyst by S. Salomons; R.E. Hayes; M. Votsmeier; A. Drochner; H. Vogel; S. Malmberg; J. Gieshoff (pp. 305-313).

This paper presents experiments and model predictions for the oxidation of CO over a platinum catalyst in a monolith reactor. Experimental behavior is broadly consistent with previously reported work on CO oxidation. Ignition–extinction (light-off) curves demonstrated the presence of multiple steady states with a hysteresis effect. The two branches corresponding to the two states of predominantly CO covered or oxygen covered. Admission of CO pulses to an oxygen covered surface results in reaction, indicating the occurrence of adsorption of CO on an oxygen covered surface. A model based on adsorption and surface reaction using the classical Langmuir–Hinshelwood (LH) approach qualitatively was able to reproduce the light-off behavior. The best model assumes dissociative chemisorption of oxygen on two surface sites. It was superior to a model proposing molecular adsorption of oxygen followed by rapid dissociation. Addition of steps allowing CO adsorption on an oxygen filled surface via an “oxygen compression” mechanism enable the qualitative description of the reactor response to step inputs of CO to an oxygen rich feed stream. Some parameter adjustment remains to allow a better fit between experiment and model predictions.

Keywords: Light-off; Ignition; Catalytic converter; Kinetic modeling; CO oxidation; Platinum; Monolith

Catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ composite oxides for methane combustion: Influence of catalyst pretreatment temperature and oxygen concentration in the reaction mixture by L.F. Liotta; G. Di Carlo; G. Pantaleo; G. Deganello (pp. 314-322).

The influence of catalyst pre-treatment temperature (650 and 750°C) and oxygen concentration ( λ=8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ containing 30wt.% of Co₃O₄. The catalytic materials prepared by the co-precipitation method were calcined at 650°C for 5h (fresh samples); a portion of them was further treated at 750°C for 7h, in a furnace in static air (aged samples).Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12000 and 60000mLg⁻¹h⁻¹). The catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ were compared with those of two pure Co₃O₄ oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ as well as to their reducibility. Particular attention was paid to the thermal stability of the Co₃O₄ phase in the temperature range of 750–800°C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co₃O₄ heated up to 800°C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ=8, stoichiometric λ=1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co₃O₄ decomposition into CoO was observed.Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co₃O₄ and by promoting the reduction at low temperature.

Keywords: Cobalt oxide; Ceria; Ceria–zirconia; Methane combustion; Textural properties; Thermal stability

Development of new catalysts for N₂O-decomposition from adipic acid plant by Stefano Alini; Francesco Basile; Sonia Blasioli; Cinzia Rinaldi; Angelo Vaccari (pp. 323-329).

Direct decomposition of N₂O was investigated using simulated and real industrial gas stream coming from an adipic acid plant. Two different kinds of catalysts were studied: (i) LaB1−_xB′_xO₃ and CaB1−_xCu_xO₃ (B=Mn, Fe and B′=Cu, Ni) perovskites (PVKs) and (ii) supported PVKs (10 or 20wt.%) on γ-Al₂O₃ and CeO₂–ZrO₂. The structural modifications induced by the composition of PVK samples affect the catalytic performances: mixed oxide formation in CaMn_0.7Cu_0.3O₃ samples allows to reach the highest values of N₂O conversion while the effect of PVK phases is more controversial. The importance of copper on catalytic activities is confirmed by the investigation on CaMn1−_xCu_xO₃ samples. The best results were obtained with a CaMn_0.6Cu_0.4O₃ catalyst calcined at 700°C for 5h, in which the presence of copper maximises the Ca₃CuMnO₆ phase formation. The increase in Cu-content produces a large segregation of CuO despite PVK formation. The best catalyst was tested using industrial gas stream, showing good stability also in the presence of H₂O and O₂ (8%v/v ) after 1400h on-stream. To increase surface area, Cu-containing PVKs were deposed on γ-Al₂O₃ and CeO₂–ZrO₂, and this latter has been recognised as the best support. Indeed, the activity of the PVKs supported on ceria–zirconia is comparable to and even better than that of the bulk catalysts. A possible explanation regards the support contribution in terms of activity and/or promotion of O₂ mobility which enhances the overall activity of the catalyst.

Keywords: Adipic acid plant; CaMnCuO catalyst; CeO; ₂; –ZrO; ₂; support; N; ₂; O-decomposition; Perovskites; Real industrial conditions; Supported perovskites

Nitrous oxide formation in low temperature selective catalytic reduction of nitrogen oxides with V₂O₅/TiO₂ catalysts by Juan Antonio Martín; Malcolm Yates; Pedro Ávila; Silvia Suárez; Jesús Blanco (pp. 330-334).

Nitric oxide and nitric dioxide compounds (NO_x) present in stack gases from nitric acid plants are usually eliminated by selective catalytic reduction (SCR) with ammonia. In this process, small quantities of nitrous oxide (N₂O) are produced. This undesirable molecule has a high greenhouse gas potential and a long lifetime in the atmosphere, where it can contribute to stratospheric ozone depletion. The influence of catalyst composition and some operating variables were evaluated in terms of N₂O formation, using V₂O₅/TiO₂ catalysts. High vanadia catalyst loading, nitric oxide inlet concentration and reaction temperature increase the generation of this undesirable compound. The results suggest that adsorbed ammonia not only reacts with NO via SCR, but also with small quantities of oxygen activated by the presence of NO. The mechanism proposed for N₂O generation at low temperature is based on the formation of surface V–ON species which may be produced by the partial oxidation of dissociatively adsorbed ammonia species with NO+O₂ (eventually NO₂). When these active sites are in close proximity they can interact to form an N₂O molecule. This mechanism seems to be affected by changes in the active site density produced by increasing the catalyst vanadia loading.

Keywords: Nitrous oxide; Vanadia-titania catalysts; Selective catalytic reduction; Dual site mechanisms

Catalytic reduction of N₂O over steam-activated FeZSM-5 zeolite by M.N. Debbagh; C. Salinas Martínez de Lecea; J. Pérez-Ramírez (pp. 335-341).

The catalytic reduction of N₂O by CH₄, CO, and their mixtures has been comparatively investigated over steam-activated FeZSM-5 zeolite. The influence of the molar feed ratio between N₂O and the reducing agents, the gas-hourly space velocity, and the presence of O₂ on the catalytic performance were studied in the temperature range of 475–850K. The CH₄ is more efficient than CO for N₂O reduction, achieving the same degree of conversion at significantly lower temperatures. The apparent activation energy for N₂O reduction by CH₄ was very similar to that of direct N₂O decomposition (140kJmol⁻¹), being much lower for the N₂O reduction by CO (60kJmol⁻¹). This suggests that the reactions have a markedly different mechanism. Addition of CO using equimolar mixtures in the ternary N₂O+CH₄+CO system did not affect the N₂O conversion with respect to the binary N₂O+CH₄ system, indicating that CO does not interfere in the low-temperature reduction of N₂O by CH₄. In the ternary system, CO contributed to N₂O reduction when methane was the limiting reactant. The conversion and selectivity of the reactions of N₂O with CH₄, CO, and their mixtures were not altered upon adding excess O₂ in the feed.

Keywords: FeZSM-5; N; ₂; O; Decomposition; Reduction; SCR; CH; ₄; CO; O; ₂; Tail-gases

Role of active oxygen transients in selective catalytic reduction of N₂O with CH₄ over Fe-zeolite catalysts by Takeshi Nobukawa; Kou Sugawara; Kazu Okumura; Keiichi Tomishige; Kimio Kunimori (pp. 342-352).

Sharp NO and O₂ desorption peaks, which were caused by the decomposition of nitro and nitrate species over Fe species, were observed in the range of 520–673K in temperature-programmed desorption (TPD) from Fe-MFI after H₂ treatment at 773K or high-temperature (HT) treatment at 1073K followed by N₂O treatment. The amounts of O₂ and NO desorption were dependent on the pretreatment pressure of N₂O in the H₂ and N₂O treatment. The adsorbed species could be regenerated by the H₂ and N₂O treatment after TPD, and might be considered to be active oxygen species in selective catalytic reduction (SCR) of N₂O with CH₄. However, the reaction rate of CH₄ activation by the adsorbed species formed after the H₂ and N₂O or the HT and N₂O treatment was not so high as that of the CH₄+N₂O reaction over the catalyst after O₂ treatment. The simultaneous presence of CH₄ and N₂O is essential for the high activity of the reaction, which suggests that nascent oxygen species formed by N₂O dissociation can activate CH₄ in the SCR of N₂O with CH₄.

Keywords: Nitrous oxide; Fe-MFI; TPD; EXAFS; FTIR; Methane activation; Nascent oxygen

Kinetic analysis of N₂O decomposition over calcined hydrotalcites by L. Obalová; V. Fíla (pp. 353-359).

Kinetics of N₂O decomposition over catalyst prepared by calcination of Co–Mn hydrotalcite was examined in integral fixed-bed reactor (V˙/w=12–96lgcat−1h−1) at various N₂O and O₂ initial partial pressure at temperature range of 330–450°C. Kinetic data were evaluated by linear and non-linear regression method, 15 kinetic expressions were tested. Based on the obtained results a redox model of N₂O decomposition was proposed. At low pressures of O₂, adsorbed oxygen is formed by the N₂O decomposition; the N₂O chemisorption is considered as the rate-determining step. On the contrary, at high O₂ pressure it could be assumed that adsorbed oxygen species appear as a result of O₂ adsorption and the Eley–Rideal mechanism is the rate determining. N₂O decomposition is well described by the 1st rate law at N₂O and O₂ concentrations typical for waste gases.

Keywords: Nitrous oxide; Decomposition; Reaction kinetics; Hydrotalcite

Understanding the activation mechanism induced by NO_x on the performances of VO_x/TiO₂ based catalysts in the total oxidation of chlorinated VOCs by F. Bertinchamps; M. Treinen; P. Eloy; A.-M. Dos Santos; M.M. Mestdagh; E.M. Gaigneaux (pp. 360-369).

A previous investigation of the chlorobenzene combustion activity of VO_x/TiO₂, VO_x–WO_x/TiO₂ and VO_x–MoO_x/TiO₂ catalysts in the presence of NO pointed out the activation effect of NO. The suggested three-step mechanism based on catalytic performances data only was: (1) chlorobenzene is oxidized on the surface of the VO_x phase (as described by Mars–van Krevelen), (2) NO gets oxidized to NO₂, mainly on WO_x and MoO_x, and (3) the in situ produced NO₂ assists O₂ in the reoxidation of the VO_x phase thus speeding up the oxidation step of the Mars–van Krevelen mechanism. The latter effect macroscopically corresponds to the observed increase of chlorobenzene conversion. This contribution aims at validating this hypothetical mechanism by pointing out the favourable occurrence of an oxidation of NO to NO₂ on the WO_x and MoO_x phases and by pointing out the higher efficiency of NO₂ than O₂ to reoxidize the reduced VO_x sites. In addition, the present contribution clearly demonstrates that, in the absence of NO, the chlorobenzene total oxidation occurred following the Mars–van Krevelen mechanism. Moreover, a thorough characterization of the oxidation state of the vanadium proving that the improvement of the catalyst activity brought by the simultaneous presence of NO and O₂ is linked to the stronger reoxidation of the VO_x active phase. Furthermore, plotting all the catalytic activity data versus the mean vanadium oxidation level clearly depicts, for the first time, the strong dependence between them. Under a mean vanadium oxidation level of 4.82 the catalyst is inactive while above 4.87 the activity is stabilized at a high level of conversion independent of the vanadium oxidation level.

Keywords: Catalytic oxidation; VOC combustion; Dioxins; Chlorinated VOCs; Chlorobenzene; Vanadia/titania catalyst; V/W/Ti; V/Mo/Ti; NO; _x; Vanadium oxidation state

Catalytic activation of ceramic filter elements for combined particle separation, NO_x removal and VOC total oxidation by Manfred Nacken; Steffen Heidenreich; Marius Hackel; Georg Schaub (pp. 370-376).

The development of a catalytically active filter element for combined particle separation and NO_x removal or VOC total oxidation, respectively, is presented. For NO_x removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO₂–V₂O₅–WO₃ catalyst system was developed on a ceramic filter element. Different TiO₂ sols of tailor-made mean particle size between 40 and 190nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO₂-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3m²/g. Selected TiO₂-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V₂O₅ and WO₃ precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300°C, a filtration velocity of 2cm/s and an NO inlet concentration of 500vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO₂-impregnated filter element support was catalytically activated with a Pt/V₂O₅ system. Complete oxidation of propene with 100% selectivity to CO₂ was achieved at 300°C, a filtration velocity of 2cm/s and a propene inlet concentration of 300vol.-ppm.

Keywords: Catalytic filter; NO; _x; reduction; VOC oxidation; TiO; ₂; –V; ₂; O; ₅; –WO; ₃

Influence of the exchanged cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs by H.L. Tidahy; S. Siffert; J.-F. Lamonier; R. Cousin; E.A. Zhilinskaya; A. Aboukaïs; B.-L. Su; X. Canet; G. De Weireld; M. Frère; J.-M. Giraudon; G. Leclercq (pp. 377-383).

0.5wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different cations to study the influence of alkali metal cations (Na⁺, Cs⁺) and H⁺ in Pd-based catalysts on propene and toluene total oxidation. The exchange with different cations (Na⁺, Cs⁺) and H⁺ led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO₂ and H₂O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-compensating cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU>Pd/NaFAU>Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA>Pd/NaBEA>Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-compensating cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs.

Keywords: Total oxidation of VOC; Palladium; Exchanged zeolite; Adsorption

Improvement of toluene catalytic combustion by addition of cesium in copper exchanged zeolites by M.F. Ribeiro; J.M. Silva; S. Brimaud; A.P. Antunes; E.R. Silva; A. Fernandes; P. Magnoux; D.M. Murphy (pp. 384-392).

HY and HMFI zeolites exchanged with copper and cesium have been studied for the catalytic combustion of toluene (800ppm) with air. The catalysts activity has been analyzed by comparison of light-off curves and in both Cu zeolites, the addition of Cs leads to a decrease of the light-off temperature by 50°C. Temperature-programmed reduction (H₂-TPR) and EPR studies have evidenced clear differences in the characteristics of the copper species both in the presence and absence of Cs co-cations. These differences account for the nature of the active centers in the Cu zeolites for the toluene oxidation. The position and geometry of the copper ions in the zeolite matrix are of great significance for the redox behavior and activity for toluene oxidation. In both MFI and FAU structures, the bulky Cs co-cations are located in the more accessible main zeolite pores, forcing the copper ions to occupy the most stable, but less accessible positions within each structure. In the case of the MFI zeolite, the EPR study revealed that the Cs exchange resulted in an increased abundance in the number of square pyramidal Cu²⁺ ions relative to the other Cu environments. Cs co-cations also lead to an increase in the reducibility of the copper ions mainly due the reduction of protons in Cu, Cs-containing samples.

Keywords: Catalytic combustion; Toluene; Cu; Cs; MFI zeolite; Y zeolite

Additional effects of cobalt precursor and zirconia support modifications for the design of efficient VOC oxidation catalysts by F. Wyrwalski; J.-F. Lamonier; S. Siffert; A. Aboukaïs (pp. 393-399).

The influence of the ZrO₂ support modification by Y₂O₃ and the presence of ethylenediamine (“en”) during the preparation of Co/ZrO₂ were studied and compared with a reference catalyst conventionally prepared by impregnation of ZrO₂ with an aqueous solution of Co(NO₃)₂. The effect of the en/Co molar ratio ( x=1–3) was studied. Activation of cobalt species was followed by differential thermal and thermogravimetric analyses (DTA/TG) analyses and by specific surface area measurements which evidence the complete cobalt precursor decomposition at 450°C, whatever the support composition and the en/Co molar ratio. The addition of an aqueous solution of ethylenediamine to a cobalt nitrate solution led to a strong increase in the catalytic activity of the activated solids for the toluene deep oxidation as compared to the reference catalyst. The best catalytic results were explained in terms of cobalt oxides dispersion (X-ray diffraction (XRD)) and also in terms of Co-support interaction (H₂-temperature-programmed reduction (TPR)). The generated cobalt species were reducible at much lower temperatures and were more active in the toluene total oxidation. Finally, an efficient catalyst was produced combining the modifications of the support by yttrium oxide and of the precursor (use of ethylenediamine).

Keywords: Zirconia; Cobalt oxides; Ethylenediamine; Yttrium oxide; Toluene total oxidation

Ceria-based oxides as supports for LaCoO₃ perovskite; catalysts for total oxidation of VOC by Mihai Alifanti; Mihaela Florea; Vasile I. Pârvulescu (pp. 400-405).

Supported LaCoO₃ perovskites with 10 and 20wt.% loading were obtained by wet impregnation of different Ce1−_xZr_xO₂ ( x=0–0.3) supports with a solution prepared from La and Co nitrates, and citric acid. Supports were also prepared using the “citrate method”. All materials were calcined at 700°C for 6h and investigated by N₂ adsorption at −196°C, XRD and XPS. XRD patterns and XPS measurements evidenced the formation of a pure perovskite phase, preferentially accumulated at the outer surface. These materials were comparatively tested in benzene and toluene total oxidation in the temperature range 100–500°C. All catalysts showed a lower T₅₀ than the corresponding Ce1−_xZr_xO₂ supports. Twenty weight percent LaCoO₃ catalysts presented lower T₅₀ than bulk LaCoO₃. In terms of reaction rates per mass unit of perovskite calculated at 300°C, two facts should be noted (i) the activity order is more than 10 times higher for toluene and (ii) the reverse variation with the loading as a function of the reactant, a better activity being observed for low loadings in the case of benzene. For the same loading, the support composition influences drastically the oxidative abilities of LaCoO₃ by the surface area and the oxygen mobility.

Keywords: Supported perovskite; Ceria support; VOC catalytic combustion

Investigation of the preparation and activity of gold catalysts in the total oxidation of n-hexane by C. Cellier; S. Lambert; E.M. Gaigneaux; C. Poleunis; V. Ruaux; P. Eloy; C. Lahousse; P. Bertrand; J.-P. Pirard; P. Grange (pp. 406-416).

The factors affecting the preparation of Au/TiO₂ catalysts and their activity in the total oxidation of n-hexane were investigated. The mechanism of gold deposition–precipitation is discussed through comparison of the samples prepared by this method and others prepared by anion adsorption method. The influence of the pH and of the origin of TiO₂ support used are additionally addressed. The difference of gold dispersion observed between the two methods is attributed to a difference of mobility of the gold precursors during the thermal treatment rather than to a difference of dispersion over the uncalcined samples. The mechanism of gold deposition–precipitation actually involves the reactions of gold hydroxy-chloride species with the surface. Another part of the work, thus, concerned the use of the deposition–precipitation method to prepare a Au/MnO₂ catalyst. It is shown that the activity of γ-MnO₂ is directly proportional to its surface area and that the deposition–precipitation procedure decreases the surface and activity of MnO₂. However, the deposition of gold allows to avoid a too deep sintering of γ-MnO₂ and, thus, helps to somehow preserve its activity.

Keywords: Au/TiO; ₂; Au/MnO; ₂; Deposition–precipitation; Anion adsorption; VOC oxidation

Novel mesoporous chromium oxide for VOCs elimination by Anil K. Sinha; Kenichirou Suzuki (pp. 417-422).

A 3D mesoporous chromium oxide prepared by a neutral templating route showed exceptionally high capacity for the elimination of volatile organic compounds (VOCs). The material contains chromium species with mixed oxidation states as observed by XPS analysis. Although the 3D mesoporous chromium oxide had ∼0.1 times the surface area than that of mesoporous silica, the chromium oxide showed much better toluene removal ability. At ambient conditions, the material acts as a selective sorbent for VOCs, while at higher reaction temperature it can be an effective and selective deep oxidation catalyst for VOCs.

Keywords: Mesoporous materials; Chromium oxide; Volatile organic compounds; Oxidation; Adsorption

On the modification of photocatalysts for improving visible light and UV degradation of gas-phase toluene over TiO₂ by Nicolas Keller; Elodie Barraud; Florence Bosc; David Edwards; Valerie Keller (pp. 423-430).

The photocatalytic behavior of different TiO₂-based photocatalysts was reported for gas-phase toluene removal under both UV and visible light illumination, and compared to that of commercial P25 (Degussa) TiO₂. Promotion by sulfates and the use of nanosized anatase TiO₂ were reported to strongly increase the toluene removal efficiency under UV illumination. Nanosized-anatase was prepared by a protecting group sol–gel synthesis using hexamethyldisilazane as crystallite growth inhibitor. Sulfates played a double positive role, with photogenerated electrons transfer effects limiting charge recombination and as repulsive species for strongly adsorbed aromatic intermediates that act as poisons. The decrease in particle size obtained on nanosized anatase TiO₂ (5nm) yielded a considerable enhancement in the toluene removal efficiency. Pure high surface area rutile has been synthesized at low temperature by a polyethylenglycol-containing sol–gel method for visible light activation purposes. A two-way semiconductor coupling phenomenon, consisting of a reciprocal electron/hole transfer between two visible light-activated oxides, rutile TiO₂ and WO₃, was proposed to explain the large gain in efficiency when adding low amounts of WO₃ to rutile TiO₂.

Keywords: TiO; ₂; Semiconductor coupling; High surface area rutile; WO; ₃; Toluene; Nanoparticles

Photocatalytic activities of NH₃-treated titanias modified with other elements by Hirotaka Ozaki; Naho Fujimoto; Shinji Iwamoto; Masashi Inoue (pp. 431-436).

Nanocrystalline titanias were obtained by thermal reaction of titanium tetraisopropoxide in 1,4-butanediol (glycothermal reaction). In this study, titanias modified with various elements (B, Mg, Al, P, Zn, and Ga) were prepared by the glycothermal method. The obtained samples were nitrified and their physical and photocatalytic properties were investigated. Among the six modifiers examined, addition of P was the most effective for photocatalytic decomposition of acetaldehyde under visible-light irradiation. After nitrification and annealing, the P-modified titania showed a strong absorption in the visible region (400–550nm). It was found that the photocatalytic activity was related to the amount of nitrogen atoms doped in the anatase structure.

Keywords: Visible-light photocatalyst; Nitrogen-doping; Nanocrystals; Glycothermal method

Copper- and iron-pillared clay catalysts for the WHPCO of model and real wastewater streams from olive oil milling production by Simona Caudo; Gabriele Centi; Chiara Genovese; Siglinda Perathoner (pp. 437-446).

The properties of copper-based pillared clays (Cu-PILC) have been studied and compared with those of the analogous iron-based clays (Fe-PILC) in the wet hydrogen peroxide catalytic oxidation (WHPCO) of model phenolic compounds ( p-coumaric and p-hydroxybenzoic acids) and real olive oil milling wastewater (OMW). These two catalysts show comparable performances in all these reactions, although they show some differences in the rates of the various steps of reaction. In particular, Cu-PILC shows a lower formation of oxalic acid (main reaction intermediate) with respect to Fe-PILC. Both catalysts show no leaching of the transition metal differently from other copper-based catalysts prepared by wetness impregnation on oxides (alumina, zirconia) or ion-exchange of clays (bentonite) or zeolite ZSM-5. No relationship was observed between copper reducibility in the catalyst and the performance in WHPCO, as well as between the rate of copper leaching and catalytic behavior. Cu-PILC shows a comparable activity to dissolved Cu²⁺ ions, although the turnover number is lower assuming that all copper ions in Cu-PILC are active. Cu-PILC shows a high resistance to leaching and a good catalytic performance, which was attributed to the presence of copper essentially in the pillars of the clay. A high efficiency in H₂O₂ use in the first hour of reaction with the participation of dissolved O₂ in solution was also shown. For longer reaction times, however, the efficiency of H₂O₂ use considerably decreases.

Keywords: Copper; Iron; Pillared clay; Wet hydrogen peroxide catalytic oxidation (WHPCO); H; ₂; O; ₂; Olive oil milling wastewater

Degradation of diclofenac in water by heterogeneous catalytic oxidation with H₂O₂ by Jörg Hofmann; Ute Freier; Mike Wecks; Susen Hohmann (pp. 447-451).

Diclofenac and other anti-inflammatory drugs have been detected not only in effluents of sewage treatment plants, hospitals and nursing homes but also in rivers and lakes. The heterogeneous catalytic oxidation was investigated for degradation of diclofenac. The kinetic of the degradation of the drug and of the formation of mineralization products with various heterogeneous catalysts has been studied. From the nature of the intermediate products a reaction path via hydroxylation, dehalogenation and cleavage of the NH-bridge between the aromatic rings is proposed. Subsequent oxidative ring opening and stepwise degradation lead to carboxylic acids.

Keywords: Diclofenac; Catalysts; Degradation; Heterogeneous catalytic oxidation; Drugs

Iron species incorporated over different silica supports for the heterogeneous photo-Fenton oxidation of phenol by F. Martínez; G. Calleja; J.A. Melero; R. Molina (pp. 452-460).

Iron-containing catalysts have been prepared following different synthesis routes and silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials were assessed on the photo-Fenton degradation of phenolic aqueous solutions using near UV irradiation (higher than 313nm) at room temperature and initial neutral pH. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. Aromatic compounds and carboxylic acids as by-products coming from incomplete mineralization of phenol as well as the efficiency of each catalytic system in the use of the oxidant were also studied. Stability of the materials throughout the photo-Fenton reaction was evaluated in terms of metal leachibility. Activity and stability depend on the environment of iron species and features of silica support. The evolution of pH with the reaction time and their relationship with TOC degradation and leaching degree has been discussed. A nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability.

Keywords: Photo-Fenton; Heterogeneous catalysts; SBA-15; Phenol

Influence of activated carbon upon titania on aqueous photocatalytic consecutive runs of phenol photodegradation by J. Matos; J. Laine; J.-M. Herrmann; D. Uzcategui; J.L. Brito (pp. 461-469).

The photocatalytic degradation of phenol was performed at room temperature in aqueous suspended mixtures of TiO₂ and activated carbon (AC). The main objective of the present work was to verify the potential of TiO₂/AC system in the photocatalytic degradation of phenol and the principal intermediate products after performing three consecutive runs. The phenol disappearance follows a first-order kinetics. Therefore, the apparent first-order rate constant of phenol and total organic carbon photodegradations were selected to evaluate the photoefficiency of the system. From the present results it can be concluded that there is a synergistic effect between both solids which is determined by the numbers of photocatalytic runs. From a practical point of view, TiO₂/AC is able to photomineralize phenol and total organic carbon for three and two, respectively, consecutive runs more efficiently than TiO₂ alone.

Keywords: Phenol; Total organic carbon; Photodegradation; Titania; Activated carbon; Kinetics; Synergy

Photocatalytic degradation of Chromotrope 2R using nanocrystalline TiO₂/activated-carbon composite catalysts by Wendong Wang; Cláudia Gomes Silva; Joaquim Luís Faria (pp. 470-478).

Composite catalysts made of nanocrystalline TiO₂ and carbon were prepared by a modified sol–gel method over activated carbon (AC). The composite catalysts were characterized by N₂ adsorption–desorption isotherm, TG, diffuse reflectance UV–vis spectroscopy, XRD and SEM. The photocatalytic activity was tested on the degradation of Chromotrope 2R (C2R) in aqueous medium under UV radiation. The composite catalysts exhibited higher activities than commercial Degussa P25 alone and the photocatalytic process was more efficient than the pure photolytic degradation. A modified Langmuir–Hinshelwood approach was used to study the kinetics and to determine the adsorption equilibrium constant and the reaction rate constant. Two different mechanisms are proposed and discussed in order to explain the observed synergy.

Keywords: Photocatalysis; UV photodegradation; Titanium dioxide; Activated carbon; Composite catalyst

Electrochemical removal of antibiotics from wastewaters by C. Carlesi Jara; D. Fino; V. Specchia; G. Saracco; P. Spinelli (pp. 479-487).

Electro-oxidation tests with different anodes (Ti/Pt, DSA^® type, graphite and three-dimensional (3D) electrode made of a fixed bed of activated carbon pellets) were performed on aqueous solutions containing the antibiotics Ofloxacin and Lincomycin. The effectiveness of the treatment of wastewater containing pharmaceuticals was assessed, as well as the electro-oxidation mechanism.The use of high electrode potentials (>2.8V versus NHE) ensured either significant anodic surface activation or minimization of fouling by in situ generated polymeric material. The use of a membrane-divided cell showed positive aspects in terms of molecule demolition, and average power consumption. The electro-oxidation was found to occur with first order kinetics mainly at anode surface when using Na₂SO₄ at low concentration (0.02N). Under these conditions, Ofloxacin is efficiently oxidized over all tested anodes (e.g. 50mgcm⁻²A⁻¹h⁻¹ for the bi-dimensional Ti/Pt electrode), whereas Lincomycin is oxidized with slow overall kinetics mainly due to difficult deprotonation, a step that precedes the primary electron transfer stage of the oxidation process. The three-dimensional electrode would be the most appropriate for continuous industrial-scale process. However, at the used potential, unacceptable corrosion of the carbon based electrode was noticed.

Keywords: Electrochemical oxidation; Antibiotics; Ofloxacin; Lincomycin; Three-dimensional electrodes; Wastewater treatment

On-board diesel fuel processing for an SOFC–APU—Technical challenges for catalysis and reactor design by A. Lindermeir; S. Kah; S. Kavurucu; M. Mühlner (pp. 488-497).

To satisfy the future needs of electrical power in passenger cars and trucks, Webasto AG develops an auxiliary power unit (APU), based on a high temperature solid oxide fuel cell (SOFC). The fuel gas for the stack is generated by catalytic partial oxidation (CPO) of diesel fuel, using a reformer without an additional water supply. This minimizes system complexity, control effort and production costs. This article focuses on experimental results of a diesel reformer and the preliminary work for the supply of a suitable unit for the generation of the fuel/air mixture. Measurements of start-up and steady state operation of the vaporizer are diagrammed, followed by a brief summary of the results obtained from laboratory scale tests. Based on these results, two different CPO reformer concepts are developed and tested under realistic conditions to evaluate their potential. Finally, the current status of system integration for a self-sustaining and stand-alone diesel APU is summarized.

Keywords: Auxiliary power unit; Fuel processing; Diesel reforming; Catalytic partial oxidation; Hydrogen generation

Noble metal catalysts supported on gadolinium doped ceria used for natural gas reforming in fuel cell applications by Ulrich Hennings; Rainer Reimert (pp. 498-508).

An attractive possibility to simplify a fuel cell system would be the use of a sulfur-tolerant reforming catalyst. In an effort to find such a catalyst, platinum, rhodium and ruthenium catalysts supported on ceria doped with 20% gadolinium and on pure ceria were synthesized and characterized. A temperature-programmed reduction study of the reduction behavior of the catalysts showed that the doping of ceria with gadolinium enhances the low temperature reduction, while the high temperature reduction is suppressed. The activity as well as the stability of the catalysts can be correlated with the reducibility of the materials. The most stable catalyst, rhodium supported on gadolinium doped ceria, shows promising sulfur-tolerance.

Keywords: Ceria; Gadolinium; Rhodium; Fuel cells; Reforming; Sulfur; Poisoning; Metal-decoration

Hydrogen production by autothermal reforming of sulfur-containing hydrocarbons over re-modified Ni/Sr/ZrO₂ catalysts by Kazuhisa Murata; Masahiro Saito; Megumu Inaba; Isao Takahara (pp. 509-514).

The catalytic autothermal reforming (ATR) of liquid hydrocarbons to provide hydrogen for mobile or stationary fuel cells was carried out over a Ni/Sr/ZrO₂ catalyst that is active for steam reforming (SR). The catalyst system was found to be active for the ATR reaction, although the hydrogen concentration obtained by ATR, under the conditions employed, was a little lower than that for SR. Addition of sulfur, introduced in the form of thiophene, reduced the catalytic stability of Ni/Sr/ZrO₂, even at 1073K. The catalyst lifetime decreased with increasing sulfur concentration between 0 and 100ppm. Additives for improving the sulfur-tolerance of Ni/Sr/ZrO₂ were examined, and additions of Re or La were found to be effective in improving the stability of the catalysts. The best catalyst was 5wt.% Re–Sr/Ni/ZrO₂. This catalyst was used in the ATR of liquid hydrocarbon fuels such as commercial premium gasoline, hydrotreated FCC gasoline, reagent mixtures, and methylcyclohexane. For premium gasoline, the activity remained unchanged during 30h, but then diminished rapidly. With the other fuels, however, the catalyst showed a much improved performance, indicating that the presence of sulfur could be associated with catalyst stability. ATR coupled with the water–gas shift reaction led to a reduction in the CO concentration by up to 2800ppm. The catalyst's activity remained constant even after cold-start runs with 853–423–853K temperature cycles under H₂O/O₂/N₂ conditions. Thus, the Re–Sr/Ni/ZrO₂ catalyst is effective for ATR of liquid hydrocarbon fuels. Further work is currently under way to extend the catalyst life.

Keywords: Sulfur-tolerant catalyst; Autothermal reforming; Liquid hydrocarbon fuels; Hydrogen

Conditioning of Rh/α-Al₂O₃ catalysts for H₂ production via CH₄ partial oxidation at high space velocity by Alessandra Beretta; Tiziana Bruno; Gianpiero Groppi; Ivan Tavazzi; Pio Forzatti (pp. 515-524).

Experimental evidence and literature indications suggest that the process of methane partial oxidation over Rh catalysts is structure sensitive. Crystal phases and Rh cluster size are thus expected to affect the final catalytic performance. In this work, it is observed that outstanding performances are obtained when the as-prepared catalysts are conditioned through repeated runs at increasing temperature and O₂/CH₄=0.56. Catalysts slowly activate, that is CH₄ conversion and synthesis gas selectivity progressively grow with time on stream. On the basis of TPO and CH₄ decomposition measurements, this phenomenon is herein explained as the result of a surface reconstruction driven by the repeated exposition to the reaction at high temperature; it is thought that such reconstruction tends to eliminate defect sites and disfavors C-deposition reactions (extremely fast over steps and kinks). Conditioning with O₂-enriched feed streams makes conditioning faster, since the accumulation of surface C-species is suppressed; however, the catalyst is eventually less active than a catalyst conditioned with standard feed mixtures. As an alternative, accumulation of carbon can be suppressed and surface reconstruction proceeds faster if the catalyst is directly exposed to the reaction at high temperature for several hours.

Keywords: CH; ₄; partial oxidation; Rh/α-Al; ₂; O; ₃; Rh reconstruction; Structure sensitivity of C–H bond activation

Fuel processor based on syngas production via short contact time catalytic partial oxidation reactors by Stefania Specchia; Giovanna Negro; Guido Saracco; Vito Specchia (pp. 525-531).

Short contact time catalytic partial oxidation (SCT-CPO) of natural gas is a promising technology for syngas production, representing an appealing alternative to existing processes. The high conversion and selectivity observed since the earlier works in this field can make this process attractive. Moreover, the SCT-CPO reactors can be autothermally operated and the possibility to use air as oxidant appears a feasible route to reduce syngas production costs: these two issues make possible the use of a SCT-CPO reactor as the reformer of a fuel processor for H₂ production for fuel cells.The present work refers to an experimental study of syngas production from CH₄ and O₂ via a SCT-CPO reactor made of a fixed bed of Rh/α-Al₂O₃ spheres. The main obtained results are: (i) an increase in GHSV produces an enhancement of transport rates and this in turn determines an improvement in CH₄ conversion, despite the reduction in residence time; (ii) the catalyst pellets get hotter than the gas phase thus favouring the H₂ and CO production; syngas formation is in fact both thermodynamically and kinetically promoted at high temperatures; (iii) a similar improvement of conversion was obtained with a reduction of the catalyst particle size, thanks once again to an increase in the heat transport and a higher geometrical surface area of the catalyst itself. By a slight increase of the O₂ fed to the reactor, H₂ and CO yields can be maximised and a complete CH₄ conversion achieved.

Keywords: Syngas production; Methane; Catalytic partial oxidation; Short contact time; Fixed bed reactor; Rhodium catalyst

MnO_x/Pt/Al₂O₃ catalysts for CO oxidation in H₂-rich streams by J.L. Ayastuy; M.P. González-Marcos; J.R. González-Velasco; M.A. Gutiérrez-Ortiz (pp. 532-541).

The catalytic activity of Pt on alumina catalysts, with and without MnO_x incorporated to the catalyst formulation, for CO oxidation in H₂-free as well as in H₂-rich stream (PROX) has been studied in the temperature range of 25–250°C. The effect of catalyst preparation (by successive impregnation or by co-impregnation of Mn and Pt) and Mn content in the catalyst performance has been studied. A low Mn content (2wt.%) has been found not to improve the catalyst activity compared to the base catalyst. However, catalysts prepared by successive impregnation with 8 and 15wt.% Mn have shown a lower operation temperature for maximum CO conversion than the base catalyst with an enhanced catalyst activity at low temperatures with respect to Pt/Al₂O₃. A maximum CO conversion of 89.8%, with selectivity of 44.9% and CO yield of 40.3% could be reached over a catalyst with 15wt.% Mn operating at 139°C and λ=2. The effect of the presence of 5vol.% CO₂ and 5vol.% H₂O in the feedstream on catalysts performance has also been studied and discussed. The presence of CO₂ in the feedstream enhances the catalytic performance of all the studied catalysts at high temperature, whereas the presence of steam inhibits catalysts with higher MnO_x content.

Keywords: CO oxidation; Selective CO oxidation; Pt catalyst; Selectivity; MnO; _x

Reactivity of olefins in the hydrodesulfurization of FCC gasoline over CoMo sulfide catalyst by Makoto Toba; Yasuo Miki; Takashi Matsui; Masaru Harada; Yuji Yoshimura (pp. 542-547).

To achieve selective hydrodesulfurization (HDS) of fluid catalytic-cracked (FCC) gasoline for producing sulfur-free gasoline ( S<10ppm), the reactivity of various olefins contained in FCC gasoline on CoMoP/Al₂O₃ sulfide catalysts was investigated. Isomerization of the CC double bond from the terminal position to an internal position was observed. The steric hindrance around the CC double bond suppresses the reactivity of olefin hydrogenation. The sulfidation temperature of the catalyst has a major influence on olefin hydrogenation active sites. Addition of the appropriate amount of cobalt (Co/Mo ratio approximately 0.6) contributes to the suppression of olefin hydrogenation at high reaction temperature (260°C). From the comparison of catalytic performance and characterization of our CoMoP/Al₂O₃ catalyst with an analogous commercial catalyst, it is suggested that the hydrogenation of olefins depends not only on the state of the Mo CUS but also on the steric effects of both olefin structure and MoS₂ crystalline structure.

Keywords: FCC gasoline; Hydrogenation; Olefin; Cobalt molybdenum catalyst; Hydrodesulfurization

Molybdocobaltate cobalt salts: New starting materials for hydrotreating catalysts by Carole Lamonier; Catherine Martin; Jean Mazurelle; Virginie Harlé; Denis Guillaume; Edmond Payen (pp. 548-556).

This paper deals with the use of Anderson heteropolyanions as alternative starting materials to the ammonium heptamolybdate and cobalt nitrate for the preparation of hydrotreatment oxidic precursors. Ammonium and cobalt salts of molybdocobaltate anions were synthesized and impregnated on alumina. The evolution of these compounds along the different steps of preparation of the oxidic precursors has been followed using various physical techniques such as Raman, XAS and UV–vis spectroscopies. It has been shown that the nature of the surface oxomolybdenum phase strongly depends on the nature of the starting salt. After sulfidation under H₂/H₂S, the performances of these new catalysts have been evaluated in hydrodesulfuration of thiophene. It appears that the cobalt salt of the decamolybdocobaltate anion [Co₂Mo₁₀O₃₈H₄]⁶⁻, with a Co/Mo ratio equal to 0.5, allows us to improve the catalytic conversion by comparison to reference catalysts prepared with ammonium heptamolybdate and cobalt nitrate as starting materials. It has been shown that this improvement is due to the preservation of the heteropolyanionic structure up to the drying step.

Keywords: Catalysis; Hydrotreatment; Heteropolyanions

Oxidation of H₂S on activated carbon KAU and influence of the surface state by Dmitrii V. Brazhnyk; Yuri P. Zaitsev; Irina V. Bacherikova; Valery A. Zazhigalov; Jerzy Stoch; Andrzey Kowal (pp. 557-566).

Properties of the oxidized activated carbon KAU treated at different temperatures in inert atmosphere were studied by means of DTA, Boehm titration, XPS and AFM methods and their catalytic activity in H₂S oxidation by air was determined. XPS analysis has shown the existence of three types of oxygen species on carbon catalysts surface. The content of oxygen containing groups determined by Boehm titration is correlated with their amount obtained by XPS. Catalytic activity of the KAU catalysts in selective oxidation of hydrogen sulfide is connected with chemisorbed charged oxygen species (O_3.1 oxygen type with BE 536.8–537.7eV) present on the carbons surface.Formation of dense sulfur layer (islands of sulfur) on the carbons surface and removal of active oxygen species are the reason of the catalysts deactivation in H₂S selective oxidation. The treatment of deactivated catalyst in inert atmosphere at 300°C gives full regeneration of the catalyst activity at low temperature reaction but only its partial reducing at high reaction temperature. The last case is connected with transformation of chemisorbed charged oxygen species into CO groups.The KAU samples treated in flow of inert gas at 900–1000°C were very active in H₂S oxidation to elemental sulfur transforming up to 51–57mmol H₂S/g catalyst at 180°C with formation of 1.7–1.9g S_x/g catalyst.

Keywords: Hydrogen sulfide; Selective oxidation; Activated carbon

Development of mesoporous Al,B-MCM-41 materials by T.D. Conesa; J.M. Campelo; D. Luna; J.M. Marinas; A.A. Romero (pp. 567-576).

A series of aluminum–boron–silicate MCM-41 mesoporous materials and their counterparts treated with NH₄F aqueous solution were synthesized and characterized by using XRD, MAS NMR, nitrogen physisorption, DRIFT, TG-DTA, TP/MS and pyridine adsorption. All of the samples showed typical MCM-41 structural and textural properties.²⁷Al MAS NMR showed that the aluminum environment was mainly four-coordinated and six-coordinated aluminum for non-fluorinated samples and fluorinated ones, respectively. Boron was in the trigonal framework environment at ca. catalytic reaction temperatures and the NH₄F treatment did not affect the boron environment in our Al,B-MCM-41 materials. All of the Al,B-MCM-41 materials studied contained both Brønsted and Lewis acid sites. However, the strong acid Brønsted/Lewis ratios decreased in the fluorinated catalysts. Moreover, the influence of temperature was studied on the cyclohexanone oxime conversion and the product selectivity in the 623–798K range. Results indicated that temperatures lower than 748K favored Beckmann rearrangement to ɛ-caprolactam, whereas, at higher temperatures the main reaction was cyclohexanone oxime hydrolysis to cyclohexanone. The aluminum–boron–silicate MCM-41 mesoporous materials treated with NH₄F improved both the selectivity to ɛ-caprolactam (related mainly to boron content) and their life span (related to their lower ratios of strong Brønsted/Lewis acid sites).

Keywords: Mesoporous materials; MCM-41; Beckmann rearrangement; ɛ-Caprolactam; Deactivation; Fluorine

Aldol condensation of campholenic aldehyde and MEK over activated hydrotalcites by S. Abelló; F. Medina; D. Tichit; J. Pérez-Ramírez; J.E. Sueiras; P. Salagre; Y. Cesteros (pp. 577-584).

In this paper, activated Mg-Al hydrotalcites were used as catalysts in the aldol condensation of campholenic aldehyde and methyl ethyl ketone (MEK). These materials represent an attractive alternative to less environmentally friendly liquid bases in a number of base-catalyzed reactions involved in the pharmaceutical and fragrance industries. The presence of basic hydroxyl groups in the interlayer space leads to very active materials. However, the relation between the activity of reconstructed hydrotalcites and the rehydration procedure is still not well understood. Different rehydration protocols in combination with extensive characterization studies were performed, including XRD, SEM, IR spectroscopy and TPD of CH₃CN and CH₃NO₂. The materials were tested as catalysts in the aldol condensation of campholenic aldehyde and MEK, and relationships between the catalytic performance of the activated hydrotalcites and the rehydration procedure were derived. Several factors may influence the activity and selectivity of this reaction, such as the reaction temperature, the molar ratio of the reactants and the degree of rehydration of the hydrotalcite-like catalysts. The selectivity towards the formation of the desired branched isomer increases when performing the reaction at low temperatures.

Keywords: Solid base catalysis; Aldol condensation; Campholenic aldehyde; MEK; Hydrotalcite; Meixnerite; Rehydration

FT-IR spectroscopic and catalytic study of de-aluminated H-mordenites as environmental friendly catalysts in the hydroxymethylation of 2-methoxyphenol with formaldehyde in aqueous medium by M. Armandi; B. Bonelli; E. Garrone; M. Ardizzi; F. Cavani; L. Dal Pozzo; L. Maselli; R. Mezzogori; G. Calestani (pp. 585-596).

Several de-aluminated H-mordenites, prepared by treating a commercial H-mordenite (HM-16, Engelhard) with aqueous HCl solutions, were characterized and tested as catalysts in the liquid-phase hydroxymethylation of guaiacol with aqueous solutions of formalin, for the production of p-vanillic alcohol (3-methoxy-4-hydroxybenzyl alcohol), the intermediate in vanillin synthesis.Samples were obtained with Si/Al atomic ratios from 10 to 36; their acidic and hydrophilic properties have been characterized by means of FT-IR spectroscopy of adsorbed probe molecules, namely CO at nominal 77K, NH₃ and H₂O at room temperature, and ammonia TPD.De-alumination led to the development of a mesoporous structure, and to a partial structure degradation with the most de-aluminated sample (Si/Al=36).As to the acidic properties, both Brønsted species in the main channels and in side-pockets were removed, and less acidic hydroxyls formed.The catalytic performance was affected mainly by samples hydrophilicity that considerably decreased upon de-alumination. In the Si/Al ratio range investigated, a decrease in the number of acidic sites led to a complex catalytic behaviour, with a maximum activity for intermediate Si/Al ratio (=25). A higher concentration of aromatic compounds in the pores of more hydrophobic zeolites (higher Si/Al ratios) also led to a higher selectivity towards heavy, di-arylic by-products. A comparison with commercial H-mordenites having similar Si/Al ratio evidenced that the occurrence of mesoporosity, in strongly de-aluminated samples, also affected the catalytic performance, favouring the formation of bulky di-aryl compounds and leading to lower guaiacol conversion.

Keywords: Mordenite; De-alumination; Hydrophilicity/hydrophobicity; Heterogeneous catalysis; FT-IR spectroscopy; Hydroxymethylation of Guaiacol; Vanillols

Environmentally friendly, heterogeneous acid and base catalysis for the methylation of catechol: Chances for the control of chemo-selectivity by M. Ardizzi; N. Ballarini; F. Cavani; E. Chiappini; L. Dal Pozzo; L. Maselli; T. Monti (pp. 597-605).

The properties of catalysts with (i) Brønsted-type acidity (H-mordenite and Al/P mixed oxide), (ii) Lewis-type acidity (Al trifluoride) or (iii) basic characteristics (Mg/Fe mixed oxide) were investigated in the gas-phase methylation of catechol. When methanol was used as the methylating agent, H-mordenite and AlF₃ gave high selectivities to guaiacol (the product of O-methylation) under mild reaction conditions, that is at very low catechol conversions. An increase in temperature led to the transformation of guaiacol to phenol and cresols, and to considerable catalyst deactivation. The basic catalyst Mg/Fe/O also favored an extensive degradation of guaiacol to phenol. On the mildly acidic catalyst Al/P mixed oxide a stable catalytic performance and a high selectivity to guaiacol at 40% catechol conversion were obtained. When methylformate, a more reactive methylating agent, was used with AlF₃ and Mg/Fe mixed oxide as catalysts, higher catechol conversions and slower deactivation rates could be achieved under mild reaction conditions, with a low extent of guaiacol degradation. However, methylformate rapidly decomposed when temperatures above 350°C were used. Finally, tests were made by reacting catechol and diethoxymethane with acid catalysts, with the aim of synthesizing methylenedioxybenzene. The latter product was obtained with high selectivity, but with very low yield, due to both catalyst deactivation and decomposition of diethoxymethane.

Keywords: Catechol methylation; Guaiacol; Methylenedioxybenzene; Heterogeneous acid catalysis; Heterogeneous basic catalysis

Improved atom efficiency via an appreciation of the surface activity of alumina catalysts: Methyl chloride synthesis by Alastair R. McInroy; David T. Lundie; John M. Winfield; Chris C. Dudman; Peter Jones; David Lennon (pp. 606-610).

The hydrochlorination of methanol over a commercial grade η-alumina catalyst has been investigated via temperature-programmed reaction (TPR). Experiments were conducted over a temperature range of 295–1000K using: (i) a methanol-only feed stream and (ii) a methanol/HCl mixed feed stream in a 1:1 mole ratio. Methanol-only studies showed activity for the formation of dimethyl ether (DME) above 450K, consistent with temperature-programmed desorption studies. A rapid decline in DME activity and consumption of methanol at higher temperatures were observed and are attributed to a deactivation pathway, involving the conversion of methoxy species to surface formate species. At elevated temperatures these processes lead to the deposition of carbon on the substrate. The introduction of HCl to the reaction stream resulted in the formation of methyl chloride (MC) over a temperature range of 400–750K. Relatively small quantities of DME by-product were also observed over a similar temperature range. The coincidence of the reaction profiles of both MC and DME imply that the same reactive methoxy species are involved in both processes. The rate of reaction for the formation of both products declines rapidly above 700K. This is attributed to the methoxy decomposition pathway to formate and, ultimately, to carbon retention by the catalyst.The effect of carbon deposition was also investigated via a subsequent cooling process carried out immediately after TPR experiments. Reaction profiles showed comparable activity for the formation of both products with respect to initial TPR experiments. Taken together, these results indicate an optimum reaction temperature for the formation of methyl chloride from the hydrochlorination of methanol. At such temperatures, carbon deposition is minimized and high conversion is maintained.

Keywords: Alumina; Methyl chloride; Temperature-programmed reaction; Methanol; Dimethyl ether; Formate

Screening of amorphous metal–phosphate catalysts for the oxidative dehydrogenation of ethylbenzene to styrene by F.M. Bautista; J.M. Campelo; D. Luna; J.M. Marinas; R.A. Quirós; A.A. Romero (pp. 611-620).

The gas-phase oxidative dehydrogenation of ethylbenzene to styrene was carried out by using as catalyst a series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe=Al/Ca=1) mixed systems: FeAl(PO₄)₂ and Ca₃Al₃(PO₄)₅, that were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. These results were compared to those obtained with 24 commercial inorganic solids (several metal oxides, sulfates and phosphates). Reactions were also carried out without oxygen, under non-oxidative conditions, where the catalytic activity was always appreciably lower than under oxidative conditions. Experimental results indicated that the oxidative gas-phase dehydrogenation of ethylbenzene to styrene could be related to the total number of acid and basic sites of catalysts, so that this reaction probably needs selected acid–basic pairs for coke formation, where the oxidative dehydrogenation process is developed.The main practical conclusion of the catalyst screening was that the best results were obtained with the synthesized amorphous AlPO₄, where 43% ethylbenzene conversion and 99.7% styrene selectivity were achieved. A very reduced number of commercial inorganic solids like Al₂(SO₄)₃, Cr₂(SO₄)₃, Fe₂(SO₄)₃, NiSO₄, Al₂O₃ and Fe₂O₃ were also able to obtain an acceptable catalytic behavior, with conversions ranging between 18 and 23% and selectivity in the 95–100% range. Among the other synthesized solids, Ni₃(PO₄)₂-A-450 was the only metal phosphate exhibiting results in such a range. All the other catalysts studied were rather inactive and/or selective. Additional experiments carried out at longer times on stream (3.5h) and longer contact times ( W/ F 0.254 and 0.654) confirmed the superior catalytic behavior of amorphous AlPO₄. Consequently, this solid could be a good candidate for application as a catalyst in the industrial oxydehydrogenation of ethylbenzene to styrene.

Keywords: Ethylbenzene oxidative dehydrogenation; Styrene synthesis; Acid–base sites; Amorphous AlPO; ₄

Aerobic selective oxidation of (hetero)aromatic primary alcohols to aldehydes or carboxylic acids over carbon supported platinum by Cécile Donze; Pavel Korovchenko; Pierre Gallezot; Michèle Besson (pp. 621-629).

The synthesis of substituted benzaldehydes, benzoic acids, heterocyclic aromatic aldehydes and acids has been studied via the oxidation of the aromatic alcohols with air under mild pressure (<20bar) at 100°C, in the presence of a 1.95wt.% Pt/C catalyst. The solvent was found to play the most important role in determining the selectivity of the oxidation products. Changing the solvent enabled tuning the reaction either to the aldehyde (pure dioxane), or the carboxylic acid (dioxane/aqueous solution without or with addition of sodium hydroxide). This oxidation method allowed to effectively oxidize many substituted benzylalcohols with various electron-releasing or -attracting groups (NO₂, Me, OMe, Cl, Br, OH, phenyl, …) and heterocyclic alcohols including nitrogen and sulphur atoms (2-thiophenemethanol, 2- and 4-pyridine methanol compounds).

Keywords: Oxidation; Aromatic alcohol; Carbonyl compounds; Molecular oxygen; Supported platinum catalyst

Supercritical carbon dioxide as an alternative reaction medium for hydroformylation with integrated catalyst recycling by Florian Patcas; Constantin Maniut; Cezar Ionescu; Stephan Pitter; Eckhard Dinjus (pp. 630-636).

The cobalt-catalyzed hydroformylation of 1-octene using the complex bis{tri(3-fluorophenyl)phosphine}hexacarbonyldicobalt (1) and Co₂(CO)₈ as pre-catalysts in supercritical carbon dioxide (scCO₂) as a reaction medium was investigated. The catalytic performance in scCO₂ was compared to the one in toluene as a conventional solvent. Similar activities and selectivities were obtained in both reaction media. In scCO₂, a substantial improvement of the selectivity for aldehydes was found by using (1) (P:Co=1:1) in comparison to the unmodified catalyst Co₂(CO)₈ (P:Co=0:1). Surprisingly, further addition of ( m-FC₆H₄)₃P (P:Co=6:1 and 11:1, respectively) resulted in a little enhancement of the aldehydes selectivity only, whereas the conversion and, hence, the aldehydes yield were reduced. A concept for catalyst recycling by using scCO₂ was introduced. It was found that (1) was insoluble in the cold reaction mixture and was completely soluble in the supercritical reaction medium. By cooling the reactor content after the olefin conversion, the catalyst was regenerated as a solid, separated by filtration and could be recycled several times.

Keywords: scCO; ₂; Green solvent; Hydroformylation process; Cobalt catalyst; Catalyst recycling

Use of renewables for the production of chemicals: Glycerol oxidation over carbon supported gold catalysts by S. Demirel; K. Lehnert; M. Lucas; P. Claus (pp. 637-643).

As a renewable feedstock and due to its high functionality glycerol is an attractive reactant for the production of a large number of valuable compounds. We report on an environmentally friendly alternative to produce chemicals from the glycerol oxidation, which are currently produced either by stoichiometric oxidation processes or by enzymatic routes. We investigate the heterogeneously catalyzed liquid-phase oxidation of glycerol with carbon supported gold catalysts. The prepared nanosized gold catalysts are highly active, so that the reaction could be performed under atmospheric pressure. The influence of the preparation method of the catalysts has been investigated. Moreover, the support effect on the catalytic process has been studied and discussed in terms of pore structure of the investigated carbon materials. The promotor effect of platinum on Au/C catalysts was examined and it could be shown that the presence of Pt increases not only the catalyst activity but also the selectivity. By promoting the gold catalysts with platinum the selectivity to dihydroxyacetone could be increased from 26% (Au/C) to 36% (Au–Pt/C).

Keywords: Glycerol; Liquid-phase oxidation; Gold catalysts; Carbon support; Support effect; Platinum; Promotor effect; Dihydroxyacetone

A new environmental friendly method for the preparation of sugar acids via catalytic oxidation on gold catalysts by Agnes Mirescu; Ulf Prüße (pp. 644-652).

A novel and efficient way of producing of aldonic acids is reported. The selective catalytic oxidation of monosaccharides (arabinose, ribose, xylose, lyxose, mannose, rhamnose, glucose, galactose, N-acetyl-glucosamine) and disaccharides (lactose, maltose, cellobiose, melibiose) on Au, Pd and Pt catalysts was investigated. By using the gold catalyst, a total selectivity with respect to aldonic acids and a high catalytic activity for all investigated sugars was found. The reaction conditions for the production of maltobionic and lactobionic acids via oxidation on gold catalysts were optimised. A high long-term stability of two different gold catalysts for the oxidation of maltose and lactose, respectively, was found.

Keywords: Gold; Selective oxidation; Carbohydrates; Aldonic acids

Influence of the preparation conditions on the properties of gold catalysts for the oxidation of glucose by Christine Baatz; Nadine Thielecke; Ulf Prüße (pp. 653-660).

In this work, two deposition–precipitation methods for the preparation of gold catalysts for glucose oxidation were investigated. Thus far, gold colloids immobilized on carbon have been used for catalytic glucose oxidation, but the long-term stability of these systems was not sufficient. To improve the long-term stability we used the deposition–precipitation methods using NaOH (DP NaOH) or urea (DP urea) as precipitation agents as they were described by Haruta and Dekkers, respectively, using alumina as a support material. With these methods, it was possible to prepare highly active and selective catalysts which showed an excellent long-term stability. DP urea was found to be the preferred method, because in contrast to DP NaOH, no losses of gold occurred during the preparation, and it was possible to adjust various gold contents up to 10wt% Au.

Keywords: Gold catalysts; Glucose oxidation; Deposition–precipitation; Alumina; DP NaOH; DP urea

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Applied Catalysis B, Environmental (v.70, #1-4)