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Applied Catalysis B, Environmental (v.72, #1-2)

Contents Continued (pp. i).

Editorial Board/Full Title Page (pp. i).

Outside Back Cover (pp. co4).

Inside Front Cover (pp. co2).

Ruthenium and platinum catalysts supported on Ce, Zr, Pr-O mixed oxides prepared by soft chemistry for acetic acid wet air oxidation by J. Mikulová; S. Rossignol; J. Barbier Jr.; D. Mesnard; C. Kappenstein; D. Duprez (pp. 1-10).

Sol–gel Zr_0.1Ce_0.9O₂ and Zr_0.1(Ce_0.75Pr_0.25)O₂ mixed oxides and commercial pure ceria CeO₂ displaying the fluorine type structure have been used as platinum or ruthenium catalysts’ supports for catalytic wet air oxidation of aqueous solution of acetic acid (78mmolL⁻¹) chosen as a model molecule. These catalysts were prepared by conventional impregnation (5wt.%) from platinum and ruthenium precursor salts. A screening of catalysts in CWAO at 200°C under 2MPa of partial oxygen pressure was performed and reveals that the best platinum catalyst is supported on pure ceria displaying large surface area. The mineralization of acetic acid solution reached 90% after 3h of reaction on PtCe catalyst. For ruthenium catalysts, the highest conversion after 3h of reaction has been reached by the Ru/Zr-Ce-O system ( M_3h=88%). Ce(CO₃)OH species, evidenced by FT-IR and XRD, were formed during the CWAO reaction essentially on well dispersed platinum catalysts supported on mixed oxides. These carbonates were responsible of a drastic drop in catalytic performances. These carbonates were responsible of a drastic drop in catalytic performances. This carbonatation phenomenon was directly linked to the oxygen storage capacity (OSC) of the catalysts. A moderate OSC is required: when it is too high, it induces an inhibition of catalysts.

Keywords: Sol–gel; Catalytic wet air oxidation; Acetic acid; Platinum; Ruthenium; Cerium (mixed) oxide

Structure and activity of nanosized iron-doped anatase TiO₂ catalysts for phenol photocatalytic degradation by C. Adán; A. Bahamonde; M. Fernández-García; A. Martínez-Arias (pp. 11-17).

A series of nanosized iron-doped anatase TiO₂ catalysts with different iron content (between 0.4 and 5.1wt.%) has been prepared by a microemulsion method and examined with respect to their behaviour for UV photocatalytic degradation of aqueous phenol. The activity results have been correlated with structural, electronic and surface examinations of the catalysts done with XRD, Raman, UV–vis, EPR, N₂ physisorption and NH₃ chemisorption. An enhancement of the photocatalytic activity is observed for doping levels up to ca. 1wt.% which is attributable to the effective introduction of Fe³⁺ cations into the anatase structure along with associated modifications of the surface acid/base properties. Achievement of relatively high levels of surface segregation of oxidic iron-containing amorphous phases for higher doping levels results however detrimental to the photoactivity.

Keywords: Photocatalyst; Titanium dioxide; Anatase; Iron doping; Microemulsion method; XRD; Raman; EPR; UV–vis; NH; ₃; chemisorption; Phenol degradation

Environmentally friendly Baeyer-Villiger oxidation with H₂O₂/nitrile over Mg(OH)₂ and MgO by Rafael Llamas; César Jiménez-Sanchidrián; José Rafael Ruiz (pp. 18-25).

We synthesized various magnesium hydroxides and calcined them to obtain oxides that were used as catalysts in the Baeyer-Villiger (BV) oxidation of cyclohexanone with a mixture of 30% aqueous hydrogen peroxide and benzonitrile as oxidant. The magnesium hydroxide obtained by precipitation from the nitrate was found to be the catalyst providing the highest conversion to ɛ-caprolactone and initial catalytic activity among all studied. Also, all hydroxides proved more active than their corresponding oxides in the BV reaction. The addition of an anionic surfactant had a favourable effect on the reaction that is explained by formulating a consistent mechanism. Finally, the influence of the variables involved in the process was examined in depth in order to bring the operating conditions as close as possible to those usable on an industrial scale.

Keywords: Magnesium hydroxide; Baeyer-Villiger oxidation; Hydrogen peroxide; Nitrile

Humic acid modified Fenton reagent for enhancement of the working pH range by A. Georgi; A. Schierz; U. Trommler; C.P. Horwitz; T.J. Collins; F.-D. Kopinke (pp. 26-36).

The suitability of the Fenton process for the remediation of soil and groundwater is limited by the necessity to acidify the reaction medium. This study examines the applicability of humic acid (HA) as an iron chelator in a modified Fenton system with the aim of extending the optimum pH range for this process towards neutral conditions. Addition of HA at a concentration of 50–100mgL⁻¹ greatly enhances the rate of oxidation of organic compounds in a catalytic Fenton system in the range of pH 5–7. Similar rates at pH 5 in the presence of HA can be achieved as at pH 3 for a typical Fenton process in the absence of HA ( k′=9×10⁻³min⁻¹ for benzene degradation atcH2O2=0.13M). A comparison of the relative reactivities of various model compounds supported the hypothesis that OH radicals are the main reactive species in the HA-modified Fenton system. In contrast, however, another type of chelated Fe-catalyst (Fe-TAML) proved to be more selective than expected for OH radicals. A long-term study revealed that the HA itself is oxidized and thereby loses its ability to enhance the degradation of the pollutant molecules. Therefore, the HA-modified Fenton system is effective for degrading pollutants which are at least as reactive towards OH radicals as the HA itself, such as BTEX, phenols or PAHs. The results obtained indicate that the HA-modified Fenton system is also applicable for compounds with a high sorption tendency towards HA.

Keywords: Hydrogen peroxide; Humic substances; Fenton; Iron chelators; AOP

Selective catalytic reduction of NO by ammonia on V₂O₅–SO₄²⁻/TiO₂ catalysts prepared by the sol–gel method by L. Baraket; A. Ghorbel; P. Grange (pp. 37-43).

This paper examines the effect of sulfation of vanadia–titania binary solid prepared by sol–gel process on its activity for the selective catalytic reduction (SCR) of NO with NH₃. Sulfated and unsulfated vanadia titania have been characterized by means of N₂ adsorption–desorption at 77K, XRD, TGA, propan-2-ol conversion as acid test, H₂-TPR measurements, EPR, XPS and Raman spectroscopies.The main results of this study highlight the interaction of sulfate ions with vanadia species. The ternary catalyst VTiS exhibits a high activity compared to binary TiS or VTi samples. It is concluded that sulfate species improve the superficial acidity of solid and interact with vanadia leading to a better reducibility of VTiS oxide.

Keywords: Sol–gel; Sulfate; Vanadia; Titania; SCR

Cracking of a rapeseed vegetable oil under realistic FCC conditions by Xander Dupain; Daniel J. Costa; Colin J. Schaverien; Michiel Makkee; Jacob A. Moulijn (pp. 44-61).

A rapeseed vegetable oil, pure and blended with conventional FCC feedstock, has been catalytically cracked with a commercial equilibrium catalyst under realistic FCC conditions. The rapeseed oil can be converted into gasoline- and diesel-range hydrocarbons that are low in sulfur and nitrogen. The triglycerides are predominately converted within 50ms at 485–585°C into fatty acids through radical cracking reactions. Relatively high amounts of coke are formed. The high aromatisation rate of the fatty acids causes the formation of large amounts of aromatics of up to 30–40wt.% in the gasoline fraction. Due to the high aromaticity the product is hardly subject to serial cracking reactions and the lower olefins yield (C^₃ and C^₄) remains low. The rate of aromatisation is highly dependent on the olefinicity of the fatty acid and the reaction temperature. The catalytic conversion of the carbon–carbon bond saturated stearic acid results in a higher gasoline yield (57wt.% versus 34wt.% for the rapeseed oil) with a much lower aromaticity (13wt.% in gasoline versus 32wt.% in gasoline for the rapeseed oil). Due to the lower aromaticity the serial cracking reactions to the lower olefins are much better (7wt.% C^₃ and 7wt.% C^₄). In all cases, the oxygen from the fatty acids is evolved predominantly as water. Other oxygenates have not been observed in significant quantities.

Keywords: Fluid catalytic cracking (FCC); Vegetable oil; Rapeseed oil; Oleic acid; Stearic acid

Kinetic study of the hydrodesulfurization of dibenzothiophene over molybdenum carbides supported on functionalized carbon black composite by A. Hynaux; C. Sayag; S. Suppan; J. Trawczynski; M. Lewandowski; A. Szymanska-Kolasa; G. Djéga-Mariadassou (pp. 62-70).

Different carbon black composite (CBC) supported molybdenum carbides were synthesized. The support was functionalized with nitric acid at different pH of the impregnation solution (pH 5.2; 0), in order to improve the active phase dispersion. After characterization of these supported catalysts, the kinetic study of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was for the first time performed over functionalized CBC supported molybdenum carbides. It was found that the HDS of DBT proceeds via the two classical parallel routes: the hydrogenation route (HYD) leading to cyclohexylbenzene and bicyclohexyl and the direct desulfurization route (DDS) leading to biphenyl. In all cases the DDS route was more favored than the HYD route, as well as more inhibited by indole. A global kinetic model suitable for all catalysts is proposed. It could describe all experimental data, and global rate constants were calculated for the HDS of DBT. The corresponding detailed kinetics of the HDS of DBT was also put forward, considering two types of active sites and expressions for the global rate constant could be determined. Furthermore, when the CBC support was preoxidized with HNO₃, the dispersion of the molybdenum carbide active phase was improved and a higher HDS activity was observed both in the absence or in the presence of indole.

Keywords: Hydrodesulfurization; Dibenzothiophene; Hydrodenitrogenation; Indole; Molybdenum carbide; Carbon support; Oxidative treatment; Kinetics; Modelization

Deactivation of diesel oxidation catalysts: Vehicle- and synthetic aging correlations by Jonas Andersson; Matilda Antonsson; Lisa Eurenius; Eva Olsson; Magnus Skoglundh (pp. 71-81).

Deactivation characteristics of a diesel oxidation catalyst subjected to controlled lab aging were compared to field-aged catalysts after 0, 80,000, and 160,000km driving in order to establish the (dis)similarities between the two types of aging, and determine to what extent vehicle aging can be replaced by rapid synthetic aging. Emission tests confirmed the increasing deactivation of the field-aged catalysts and measurements of CO oxidation, Pt dispersion and hydrocarbon storage capacity were used together with XPS, TEM, and SEM–EDS to compare the performance with lab-aged catalysts. The synthetic aging was designed to account for a combination of thermal and chemical deactivation. A similar degree of Pt sintering was observed for both real and synthetic aging conditions, whereas differences arose from various contributions to the chemical deactivation. XPS showed that pre-oxidation and pre-reduction at 700°C was not sufficient to remove typical compounds of oil-derived catalyst poisons (P, Zn, Ca), which furthermore accumulated with mileage, on the vehicle-aged catalysts. The degree of sulfur poisoning of the lab-aged catalysts increased with the duration of low-temperature sulfur exposure and could not be recovered in atmospheres typical for normal driving conditions. The results show that synthetic aging can be used to simulate thermal aging and a general effect of irreversible chemical deactivation, and thereby accelerate durability test procedures of various catalysts where loss of catalytic activity by time of operation is of concern.

Keywords: Oxidation catalyst; Accelerated aging; Deactivation; Sulfur; Phosphorous poisoning; Sintering

A comparison of NO_x adsorption on Na, H and BaZSM-5 films by Indra Perdana; Derek Creaser; Olov Öhrman; Jonas Hedlund (pp. 82-91).

NO_x adsorption in ZSM-5 films containing Na⁺, H⁺ or Ba²⁺ as counter ions was studied. NaZSM-5 films showed a superior NO_x adsorption capacity over the entire temperature range (30–350°C) in comparison with the other films. Besides the possibility to form strongly bound surface nitrate species, the presence of the Na⁺ ions in ZSM-5 resulted in a large enhancement of various weakly adsorbed species. In the HZSM-5 film, the NO_x adsorption was mainly due to physisorption, surface nitric acid and nitrosium ion (NO⁺) formation. Besides weakly adsorbed species and surface nitric acid, the NO_x adsorption in BaZSM-5 films also resulted in formation of strongly bound surface nitrate species. The nitrate species in the BaZSM-5 film were found to be resistant to NO exposure and were mainly formed through an NO₂ disproportionation pathway.

Keywords: NO; _x; adsorption; Monolith; ZSM-5 films; Counter ions

Photoelectrocatalytic degradation of 4-chlorophenol at Bi₂WO₆ nanoflake film electrode under visible light irradiation by Xu Zhao; Tongguang Xu; Wenqing Yao; Chuan Zhang; Yongfa Zhu (pp. 92-97).

To efficiently utilize the solar light and improve the photooxidation technique for wastewater purification, a new type of photoelectrode, visible light responsive Bi₂WO₆ nanoflake film, was covered onto the indium–tin oxide glass substrate via the electrostatic self-assembly deposition. The photocatalytic oxidation, electro-oxidation, and photoelectrocatalytic (PEC) oxidation of 4-chlorophenol (4-CP) in aqueous solution using the film electrode were investigated and compared under visible light irradiation ( λ>400nm). The experimental results demonstrated that 4-CP could be degraded by the nanoflake film under visible light irradiation or by applying a bias potential greater than 0.8V. Based on X-ray photoelectron spectra (XPS) analysis of the electrode after electrochemical reaction, the electropolymerization was suggested to occur in the electro-oxidation process. Furthermore, degradation efficiency of 4-CP was largely increased by combined electro-oxidation and photocatalysis. And, it is the largest at the bias potential of 2.0V. The characteristics of the PEC degradation of 4-CP were also investigated by electrochemical impedance spectroscopy (EIS). It is shown from the EIS that the PEC degradation appears to be a simple reaction on the electrode surface, suggesting that only one step of charge transfer is involved in the electrode process. The total organic carbon analysis indicated that 4-CP could be efficiently mineralized during the PEC process.

Keywords: Bi; ₂; WO; ₆; Nanoflake film; Photoelectrocatalytic degradation; 4-CP; Visible light

A comparison of the electrooxidation kinetics of p-methoxyphenol and p-nitrophenol on Sb-doped SnO₂ surfaces: Concentration and temperature effects by C. Borras; C. Berzoy; J. Mostany; J.C. Herrera; B.R. Scharifker (pp. 98-104).

We discuss the role of the phenol substituent on the kinetics of electrochemical oxidation on metal oxide surfaces. Using UV–vis spectroscopic and high performance liquid chromatographic analyses of solutions during electrolysis on antimony-doped tin oxide (Sb-SnO₂) electrodes, we established that the oxidation of p-methoxyphenol (PMP) and p-nitrophenol (PNP) follow different reaction mechanisms. The initial PNP and PMP oxidation rates are well represented as functions of the initial phenol concentrations by the Langmuir–Hinshelwood mechanism. At high concentrations of phenol in solution, the oxidation rates are controlled by surface processes. Under surface saturation conditions the formation of OH surface species required for complete oxidation is hampered, lowering the extent of PNP oxidation. The effect of temperature on the oxidation of PNP and PMP on Sb-SnO₂ electrodes was also studied. UV–vis spectroscopy of solutions during electrolysis show that the oxidation rates of both compounds follow Arrhenius behaviour; however, the fraction of the PMP initially present oxidized after the passage of a given electric charge was not affected by temperature, whilst the fraction of PNP oxidized increased with temperature. The dissimilar behaviour is ascribed to differing adsorption of PMP and PNP on the surface of the SnO₂ electrode, as established from the correspondence of kinetic data to the Langmuir–Hinshelwood mechanism.

Keywords: Electrocatalysis; Temperature; Metal oxide anode; Oxidation of organics

NO_x storage-reduction behavior of Pt–Ba/MO₂ (MO₂=SiO₂, CeO₂, ZrO₂) catalysts by M. Piacentini; M. Maciejewski; A. Baiker (pp. 105-117).

A series of Pt–Ba/MO₂ (MO₂=CeO₂, SiO₂, ZrO₂) catalysts, containing 1wt.% Pt and different Ba-loadings (4.5–28wt.%), was investigated concerning NO_x storage and reduction of the stored NO_x species by propene using pulse thermal analysis combined with mass spectrometry and temperature-programmed reaction-desorption (TPRD). Well-characterized standard Pt/Al₂O₃ and Pt–Ba/Al₂O₃ catalysts were used as references. Exposure of the catalysts to NO/O₂ pulses showed that the NO_x storage capacity of the Ba-free as well as Ba-loaded catalysts was strongly affected by the nature of the support. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption on the Ba-free catalysts revealed that the distribution of CO chemisorbing sites also depends on the nature of the support. Among the Ba-free catalysts Pt/CeO₂ exhibited the highest NO_x uptake. No NO_x uptake was observed with Pt/SiO₂. With all supports the NO_x storage capacity increased with the Ba-loading, but differently depending on the support. TPRD of catalysts after exposure to NO_x pulses revealed that the thermal stability of the stored NO_x species is affected by the nature of the support and the Ba-loading. Up to ca. 10wt.% of Ba, Pt–Ba/CeO₂ showed the highest NO_x uptake, whereas at the highest Ba-loading (28wt.%) Pt–Ba/Al₂O₃ and Pt–Ba/ZrO₂ afforded highest NO_x storage. The NO_x storage capacity depended strongly on the relative abundance of the differently stable BaCO₃ phases. To test the storage-reduction behavior, the catalysts were subjected to alternating pulses of NO/O₂ and propene at 300°C. Depending on the support different reduction behavior was observed. While reduction occurred rapidly on Pt–Ba(16.7)/Al₂O₃ and Pt–Ba(16.7)/CeO₂, it was relatively slow and incomplete on Pt–Ba(16.7)/ZrO₂. This behavior was attributed to the low surface area of the ZrO₂ support which at higher Ba-loading seems to result in partial blocking of active Pt sites.

Keywords: NO; _x; storage-reduction catalysts; Pt–Ba/ceria; Pt–Ba/zirconia; Pt–Ba/silica; Pt–Ba/alumina; NO; _x; storage; NO; _x; reduction; Propene; Effect of Ba-loading; Stability of barium nitrates; Support influence; Pulse thermal analysis; CO adsorption

Synthesis, characterization and performance of NiMo catalysts supported on titania modified alumina for the hydroprocessing of different gas oils derived from Athabasca bitumen by D. Ferdous; N.N. Bakhshi; A.K. Dalai; J. Adjaye (pp. 118-128).

In this work, a series of NiMo/Al₂O₃ catalyst was prepared using different Al₂O₃ supports modified by titania (0–9wt%). All modified supports and fresh catalysts were characterized by BET surface area, pore volume and pore diameter measurement, TPR, TPD, XRD, FTIR and Raman spectroscopy analyses. The initial activity of these catalysts were tested in a trickle-bed reactor using three different gas oils such as light gas oil (LGO), blended gas oil (blended: 50% LGO and 50% HGO) and heavy gas oil (HGO), all derived from Athabasca bitumen. Little structural change in alumina was observed with the incorporation of titania. XRD analysis showed the well dispersion of Ni and Mo on the support. Titania in alumina increased the formation of polymolybdenum oxide on the catalyst as evident from TPR and Raman analyses. Weak–intermediate–strong acid sites on the catalyst were observed at all titania concentrations. The Lewis and Bronsted acidity on the catalyst surface increased with the increase in titania concentration from 0 to 9wt%. Nitrogen conversion increased from 57 to 71wt%, from 83 to 93wt% and from 75 to 80wt% for LGO, blended and HGO, respectively and also sulfur conversion of LGO increased from 86 to 92wt% when titania concentration was increased from 0 to 9wt%. For blended and HGO, sulfur conversion was in the range 96–99wt% at all titania concentrations.

Keywords: NiMo/Al; ₂; O; ₃; catalysts; Titania; TPR; TPD; XRD; FTIR; Raman; HDN; HDS

Manganese oxide OMS-2 as an effective catalyst for total oxidation of ethyl acetate by Aditi R. Gandhe; Jeanette S. Rebello; J.L. Figueiredo; J.B. Fernandes (pp. 129-135).

This investigation focuses mainly on the use of a synthetic cryptomelane type manganese octahedral molecular sieve, OMS-2, as a catalyst for the total oxidation of ethyl acetate. OMS-2 was found to be a highly efficient catalyst giving 100% conversion and selectivity to CO₂, the final oxidation product. In addition, it was stable with time on stream and resistant to coking. A mechanism is proposed to explain the high selectivity. Presence of Mn⁴⁺-O²⁻ Lewis acid–base pairs, ability of Mn to exist as a redox couple, viz. Mn⁴⁺/Mn³⁺ and availability of facile lattice oxygen, seem to facilitate the oxidation process.

Keywords: VOCs; Ethyl acetate; Oxidation; Manganese oxide OMS-2; Mechanism

Comparative study of the chemisorptive and catalytic properties of supported Pt catalysts related to the selective catalytic reduction of NO by propylene by Areti Kotsifa; Dimitris I. Kondarides; Xenophon E. Verykios (pp. 136-148).

The chemisorptive properties of Pt/Al₂O₃, Pt/CeO₂ and Pt/ZrO₂ catalysts and of the bare supports toward nitrogen monoxide and propylene have been studied with the use of TPD and FTIR techniques and were related to their performance for the selective catalytic reduction (SCR) of NO by C₃H₆ in the presence of excess oxygen. It has been found that interaction of the investigated materials with NO at 25°C results in the formation of three types of adsorbed species, namely nitrosyl, nitrite and nitrate. The relative population and thermal stability of adsorbed NO_x species depend on the nature of the metal oxide used as support and on the deposition or not of platinum on its surface. Pt/ZrO₂ promotes NO dissociation and nitrite/nitrate decomposition at lower temperatures, compared to Pt/Al₂O₃ and Pt/CeO₂ catalysts. Platinum crystallites supported on Al₂O₃ are partially oxidized following interaction with NO, while ZrO₂ and CeO₂ are able to maintain dispersed platinum in its reduced state. Propylene is activated on the surface of the three catalysts by forming oxygenated species with the participation of oxygen originating from the support. These species are progressively oxidized with increasing temperature yielding CO and CO₂ in the gas phase, with intermediate formation of adsorbed CO species on platinum. The process, which is promoted by platinum, is more pronounced over Pt/CeO₂, followed by Pt/ZrO₂ and Pt/Al₂O₃ catalysts. The catalytic performance of the three catalysts for the SCR of NO by propylene has been investigated with respect to the effects of the nature of the support and of platinum loading (0.1–5.0wt.%) on activity and selectivity. It has been found that the Pt/ZrO₂ catalyst is much more active than Pt/CeO₂ for all metal loadings investigated, with Pt/Al₂O₃ exhibiting an intermediate performance. It is concluded that the nature of the support influences the chemisorptive properties of the catalysts investigated and concomitantly their activity for the SCR of NO by propylene.

Keywords: Nitrogen monoxide; Propylene; Selective catalytic reduction; Platinum catalyst; Al; ₂; O; ₃; ZrO; ₂; CeO; ₂; Effect of support; Effect of metal loading; TPD; FTIR

Catalytic purification of hydrogen streams by PROX on Cu supported on an organized mesoporous ceria-modified alumina by E. Moretti; M. Lenarda; L. Storaro; A. Talon; R. Frattini; S. Polizzi; E. Rodríguez-Castellón; A. Jiménez-López (pp. 149-156).

In view of the stringent CO intolerance of the proton-exchange membrane fuel cells (PEMFCs), it is essential to eliminate even trace amounts of carbon monoxide from the reformate streams. The preferential oxidation (PROX) is considered to be a promising method for CO cleaning up. Catalytic systems, based on copper supported on ceria-modified organized mesoporous alumina, were investigated for the PROX of CO in hydrogen-rich gas stream. The catalysts showed an interesting activity in the CO-PROX. The sample with the best catalytic performance was characterized by N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction by H₂ (H₂-TPR), and successive re-oxidation (TPO).

Keywords: Preferential CO oxidation; Hydrogen; PEM fuel cell; Cerium oxide; Copper; Organized mesoporous alumina

Gold supported on Fe, Ce, and Al pillared bentonites for CO oxidation reaction by J.G. Carriazo; L.M. Martínez; J.A. Odriozola; S. Moreno; R. Molina; M.A. Centeno (pp. 157-165).

A series of gold catalysts supported on Fe, Ce, and Al pillared bentonites have been prepared, characterized by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM), S_BET, and X-ray fluorescence spectrometry (XRF) techniques and tested in the CO oxidation reaction in the absence and in presence of water in the stream. The pillaring process of the natural bentonite results in an increase in the microporosity and surface area of the solid. In the gold samples, spherical arrangements of gold particles of 2–4nm around one central particle of 4–5nm are observed, the catalysts having an average gold particle size of 2.2nm. All the gold catalysts are very active, those modified with Fe and Ce being the best. The introduction of iron and cerium by pillaring increases the catalytic performances of the final gold solids. Introduced iron atoms are accessible and active centers for the gaseous CO oxidation reaction while the cerium ones promote the catalytic activity of Fe and gold atoms. Catalysts activity increases in the presence of water in the reactant stream at temperatures lower than 120°C. At room temperature, the catalytic activity increases continuously with the gaseous water concentration of up to 6700ppm.

Keywords: Gold catalysts; Fe, Ce, and Al pillared bentonites; CO oxidation

Operando FTIR study of NO_x storage over a Pt/K/Mn/Al₂O₃-CeO₂ catalyst by T. Lesage; J. Saussey; S. Malo; M. Hervieu; C. Hedouin; G. Blanchard; M. Daturi (pp. 166-177).

The storage of NO_x under lean conditions has been studied for a Pt/K/Mn/Al₂O₃-CeO₂ catalyst by operando FTIR spectroscopy. We have found that the first step of NO_x adsorption is NO oxidation, NO₂ being subsequently stored on potassium sites as nitrites; thereafter, nitrites are finally oxidized to nitrates by further NO₂ molecules. It has been pointed out that the kinetic of these processes is strongly related to NO oxidation rate, both of them being slow at low temperatures, whereas they proceed faster at high temperatures. Two different periods have been characterized during NO_x storage, a first one presenting full consumption of the nitrogen oxides, and a second one where NO and NO₂ appear in the gas phase, to finally reach a steady level; the parameters governing the length of these periods are the progressive adsorption of NO_x all along the sample and the presence of two different potassium sites, i.e. surface and bulk sites. Finally, the excellent storage properties of the catalyst studied here have been correlated with the presence of a particular phase, which has been characterized by transmission electron microscopy (TEM).

Keywords: Diesel; Lean-burn; In situ; analysis; KNO; ₃; Lean NO; _x; -Trap; NO; ₂; NO; _x; storage; Operando; FTIR; Reaction mechanism

Identifying critical factors in the regeneration of NO_x-trap materials under realistic conditions using fast transient techniques by J.P. Breen; C. Rioche; R. Burch; C. Hardacre; F.C. Meunier (pp. 178-186).

NO_x storage and reduction (NSR) catalysts are considered to be one of the most promising solutions to meet the upcoming NO_x exhaust emission regulations. However, despite the high level of activity in this area, it is surprising that most studies have been conducted under conditions that are far from realistic conditions. In the present work a fast transient apparatus has been developed to study NSR catalysts under realistic temporal conditions, i.e. where the storage time was 1–2min and the regenerative rich time was of the order of 1s. To exemplify the value of this methodology, the performance of a 1%Pt/17.5%Ba/γ-Al₂O₃ NSR catalyst was studied as a function of the temperature, rich phase duration, reductant concentration, the type of reductant and the effect of an inert gas purge. From these results it is clearly found that excess reductant to regenerate the trap at short regeneration times is advantageous and that hydrogen is a better reductant than CO. This is especially true at low temperatures where the rate of reduction of released NO_x is not sufficiently fast to allow for complete regeneration of the trap. For a given quantity of reductant, a long, low concentration rich pulse regenerates the catalyst more effectively than a short, high concentration pulse. Readsorption of NO_x released during the rich phase but not reduced quickly enough can be a significant cause of loss of trap performance. This study underlines the importance of the regeneration step in the NSR process and highlights the need to investigate these systems using fast transient techniques capable of reproducing the short regeneration times used in real systems.

Keywords: NO; _x; storage and reduction; Lean NO; _x; trap; NSR; Pt/Ba/Al; ₂; O; ₃; Regeneration; Fast transient kinetics; deNO; _x

Sulfur durability of NO_x storage and reduction catalyst with supports of TiO₂, ZrO₂ and ZrO₂-TiO₂ mixed oxides by Naoki Takahashi; Akihiko Suda; Ichiro Hachisuka; Masahiro Sugiura; Hideo Sobukawa; Hirofumi Shinjoh (pp. 187-195).

This research focuses on investigating the influence of the various compositions of TiO₂ and ZrO₂ on the NO_x removal ability over a sulfur-treated NSR catalyst. On the NSR catalyst, potassium was loaded as the NO_x storage material and platinum as the precious metal, and the ZrO₂ content was varied from 0 to 100wt%. A relatively high NO_x removal ability above 500°C was obtained with the 60 to 80wt% ZrO₂ content, and the maximum value was 70wt%, while the TiO₂-rich supports were superior below 400°C when compared to the ZrO₂-rich supports. K/Pt/ZrO₂ had a poor NO_x removal activity over the entire temperature range. The analysis of the sulfur-aged catalysts with the supports of 70wt%ZrO₂-30wt%TiO₂, pure TiO₂, and ZrO₂ indicated that the TiO₂ support presented a higher resistance to potassium sulfate-formation, while the ZrO₂ support suppressed the solid phase reaction with potassium. The catalyst with 70wt%ZrO₂-30wt%TiO₂ retained the highest amount of remaining potassium, which was neither the formed-sulfate nor the solid-phase-reacted potassium. The sulfur-deactivation of the potassium sites could increase the activity of the metallic platinum, and a suitable combination of metallic platinum with the adequate potassium sites lead to a higher NO_x removal activity for the TiO₂-rich catalysts at low temperatures. In the case of the K/Pt/ZrO₂ catalyst, almost all the potassium changed into sulfate, which caused a poor de-NO_x ability over the entire temperature range. The support's acidity is an important factor regarding the sulfur tolerance of the NSR catalyst. The ZrO₂-TiO₂ catalyst containing 70wt% ZrO₂ was verified to have the highest acid amount among the sample supports, and was supposed to be the best support against sulfur-poisoning. In addition, this support contained 60mol% ZrO₂, and favorably suppressed the solid phase reaction with potassium. These properties of the ZrO₂-TiO₂ support containing 60mol% ZrO₂ balanced the sulfur tolerance and thermal resistance, and led to its highest NO_x purification ability at high temperatures following the sulfur-aging treatment.

Keywords: NO; _x; storage and reduction catalyst; ZrO; ₂; -TiO; ₂; Potassium; Sulfur-poisoning; Thermal deterioration

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Applied Catalysis B, Environmental (v.72, #1-2)