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Applied Catalysis B, Environmental (v.61, #1-2)

IFC (pp. co2).

FULL TITLE (pp. i).

CALENDER (pp. i).

Contents continued (pp. ii).

Enhancement of adsorption and photocatalytic activity of TiO₂ by using carbon nanotubes for the treatment of azo dye by Ying Yu; Jimmy C. Yu; Cho-Yin Chan; Yan-Ke Che; Jin-Cai Zhao; Lu Ding; Wei-Kun Ge; Po-Keung Wong (pp. 1-11).

The effect of carbon nanotubes (CNTs) on the adsorption and the photocatalytic properties of TiO₂ (P25) for the treatment of azo dyes, including one monoazo dye Procion Red MX-5B, and two diazo dyes Procion Yellow HE4R and Procion Red HE3B, are investigated by Brunauer–Emmett–Teller (BET) measurement, spectrophotometer, total organic carbon (TOC), high proficiency liquid chromatography (HPLC), Raman spectroscopy (Raman), photoluminescence (PL), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM) analyses. The results show that compared with activated carbon (AC), CNTs can comparatively better improve the adsorption of the dyes onto P25 due to the strong interaction between P25 and CNTs. Residual TOC in the solutions and the amount of cyanuric acid evolved after degradation both confirm that the adsorption ability of P25 is enhanced by CNTs. CNTs also facilitate the photocatalytic activity of P25 in the degradation of the three azo dyes more efficiently than AC. With PL and EPR analysis, the mechanism of the enhancement of the photocatalytic activity of P25 by CNTs is proposed. The excited e⁻ in conduction band of TiO₂ may migrate into CNTs, of which have special structure and the ability for e⁻ transport. Thus, the possibility of the recombination of e⁻/h⁺ pairs decreases. Meanwhile, O₂ adsorbed on the surface of CNTs may accept e⁻ and formO₂⁻, which also leads to the formation ofOH in the system. Therefore, there are more radicals in the system, resulting in the quicker degradation of the dyes.

Keywords: Carbon nanotubes; Photocatalysis; Adsorption; TiO; ₂; Azo dye; Degradation

Plasma-assisted catalysis for volatile organic compounds abatement by Monica Magureanu; Nicolae B. Mandache; Pierre Eloy; Eric M. Gaigneaux; Vasile I. Parvulescu (pp. 12-20).

A dielectric barrier discharge (DBD) combined with Mn-based phosphate catalysts placed downstream of the plasma reactor was investigated experimentally for total oxidation of toluene in air. The discharge was initiated by high voltage pulses of 18kV amplitude and 12–13ns rise time. The pulse frequency increased from 14 to 80Hz, for applied voltages in the range 18–28kV. Discharge currents up to 100 A and approximately 50ns duration were obtained. No other hydrocarbons except toluene were detected in the effluent gas. The yield of carbon dioxide formed in the discharge was up to 24%. As catalysts, MnPO₄, Mn-APO-5 and Mn-SAPO-11 were tested, for temperatures up to 400°C. Under purely catalytic conditions, the best behavior for toluene total oxidation was found for Mn-SAPO-11, with a CO₂ yield up to 33%, at 400°C. The combined application of plasma and catalysis showed a remarkable synergetic effect, even at low temperature, up to 100°C, where the catalysts alone are not active. In this range, the CO₂ yield increased up to 41%, for the Mn-SAPO catalyst. At 400°C the highest CO₂ yield was obtained for MnPO₄, reaching 68%. The synergetic effect observed for the plasma–catalyst combination is attributed to ozone radicals formed in the discharge, which decompose on the catalyst surface, greatly contributing to toluene total oxidation.

Keywords: Volatile organic compounds; Plasma; Dielectric barrier discharge; Heterogeneous catalysis

Active sites and effects of H₂O and temperature on the photocatalytic oxidation of¹³C-acetic acid on TiO₂ by Michael J. Backes; Adrienne C. Lukaski; Darrin S. Muggli (pp. 21-35).

Acetic acid adsorbs both molecularly and dissociatively as acetate on titanium dioxide. Photocatalytic oxidation (PCO) oxidizes the α-carbon in acetic acid to CO₂ without forming any long-lived intermediates, while the β-carbon forms CO₂ through methoxy, formaldehyde, and formate. Elevated temperatures desorb molecularly adsorbed acetic acid and also increase the inherent activity of sites. At least two types of active sites exist for acetic acid PCO on TiO₂. Water, which is produced during PCO, redistributes molecularly adsorbed acetic acid on the surface by displacement. Water displaces at least one-third of an acetic acid monolayer and converts some molecularly adsorbed acetic acid into acetate. Acetate is the active species for PCO and molecularly adsorbed acetic acid oxidizes during PCO by first forming acetate.

Keywords: Acetic acid; Acetate; Water; Photocatalytic oxidation; TiO; ₂; Transient reaction; DRIFTS

Diesel soot oxidation over supported vanadium oxide and K-promoted vanadium oxide catalysts by Jian Liu; Zhen Zhao; Chunming Xu; Aijun Duan; Ling Zhu; Xuezhong Wang (pp. 36-46).

Several systems of vanadium oxide and K-promoted vanadium oxide catalysts which supported on different carries with the variations of V contents and K contents were prepared by incipient-wetness impregnation method. Their catalytic performances for diesel soot catalytic oxidation were investigated with temperature-programmed oxidation reaction (TPO). Spectroscopic techniques (FT-IR and UV–vis DRS) were utilized to determine the structure of VO_x species for vanadia supported on γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂. Thermal analysis techniques, including thermogravimetrical (TG-DTA) analyses and temperature-programmed reduction (TPR), were used to characterize the thermal behavior and redox properties of K promoting vanadium oxide catalysts, respectively. The results showed that the structure of supported-vanadia catalysts depends on the support materials and also on the V loading. At high V loading, VO_x species exists predominantly as polyvanadate species and V₂O₅. The catalytic activities of the catalysts for soot oxidation are correlated to their redox property and the mobility of surface atoms. The catalytic activity for soot oxidation orders as Ti>Zr>Si>Al, and the sequence for selectivity to CO₂ formation (SCO2) is Ti>Zr>Si∼Al for the catalysts over different supports. Adding potassium into supported vanadia catalysts can improve the catalytic activity of soot oxidation. And when n_(K): n_(V): n_(Ti)=4:4:100 the catalyst of K4V4/TiO₂ gives the best activity for soot combustion, i.e., the lowest reaction temperature.

Keywords: Vanadium oxide catalyst; Diesel; Soot; Oxidation; Potassium; Support

Preparation, structural characterization and photocatalytic activity of mesoporous Ti-silicates by Gyula Wittmann; Kristof Demeestere; Andr�s Dombi; Jo Dewulf; Herman Van Langenhove (pp. 47-57).

This paper focuses on structural and photocatalytic properties of ordered mesoporous Ti-silicates, prepared by both impregnation (IMP) and coprecipitation (CP) methods. Catalyst characterization was carried out by inductively coupled plasma analysis, nitrogen adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). Photocatalytic activity was evaluated for gaseous trichloroethylene (TCE) decomposition in a batch reactor under near-UV irradiation.Both the Ti incorporation method (IMP or CP) and TiO₂ content (4.7–35.0wt.%) had large effects on structural characteristics and photocatalytic activity of Ti-silicates, whereas no important effects were observed with respect to calcination temperature (200–600°C). At all conditions, TiO₂ was present as pure anatase crystallites with particle diameters in IMP catalysts of 4.4–7.0nm, being clearly smaller than those in CP ones (12.0–19.6nm). The ordered structure of the silica was at least partially preserved up to a TiO₂ content of 25wt.% (CP) and 33wt.% (IMP). With increasing TiO₂ content, specific surface area (SSA 376–805m²g⁻¹) of both CP and IMP catalysts decreased. Similar trends were observed for pore volumes (0.6–1.2mLg⁻¹) and pore diameters (4.5–7.5nm) in IMP catalysts. Initial photocatalytic TCE degradation rate constants (0.014–0.202min⁻¹) obtained with CP catalysts increased systematically with TiO₂ contents up to 35wt.%, while in IMP ones, they levelled off at TiO₂ contents above 17wt.%. TCE degradation rates obtained with CP catalysts were up to a factor of six higher than those measured applying the IMP method. This may be explained by a different TiO₂ localization in the silica structure. During IMP preparation, TiO₂ is mostly incorporated within the silica mesopores, whereas during CP synthesis, it is mainly localized on the external silica surface.

Keywords: Photocatalysis; Trichloroethylene; Gas-phase; Titanium dioxide; Silica; Mesoporous; Structural properties; Sol–gel; Impregnation

Photocatalytic degradation of acetylene over various titanium dioxide-based photocatalysts by F. Thevenet; O. Gua�tella; J.M. Herrmann; A. Rousseau; C. Guillard (pp. 58-68).

The photodegradation of acetylene (C₂H₂) was investigated over various powders or supported titanium dioxide (TiO₂) photocatalysts in air into static conditions. It was found that UV-irradiated TiO₂ is effective in order to lead to the complete mineralization of the pollutant containing a triple carboncarbon bonding without deactivating. No organic intermediates were detected in the gas phase, implying that oxidation mechanisms take place in the adsorbed phase. The efficiency of P25-Degussa and PC500-Millennium photocatalysts were compared; the mixed anatase/rutile P25-Degussa is reported as the most efficient photocatalytical material in our conditions. The topology of the photocatalyst support is reported as a significant parameter in TiO₂ efficiency. Fibre-deposited photocatalysts lead to the highest activity, and the chemical nature of the fibre did not influence the photodegradation. The influence of TiO₂ amonut, silica binder and adsorbing additives such as zeolite, and activated carbon coupled with TiO₂ photocatalyst were investigated.

Keywords: Photocatalytic degradation; Gas phase; Acetylene

Characterisation and reactivity of vanadia–titania supported SBA-15 in the SCR of NO with ammonia by Yolanda Segura; Lucjan Chmielarz; Piotr Kustrowski; Pegie Cool; Roman Dziembaj; Etienne F. Vansant (pp. 69-78).

TiO_x, VO_x and TiO_x–VO_x oxides were highly dispersed at different metal loadings on the mesoporous silica SBA-15 by the molecular designed dispersion (MDD) method. A combination of different techniques (N₂-sorption, FT-Raman, TPR, UV–vis-DR) was used to verify the nature of the vanadia and/or titania species on the surface of the mesoporous support. Temperature-programmed desorption (NH₃-TPD) was applied to characterise the surface acidity of these catalysts. Vanadia and titania were found to be present as isolated species, even at high metal oxide concentrations. The supported catalysts were tested in the selective catalytic reduction (SCR) of NO with ammonia. Among the studied samples, the highest activity was found for TiO_x–VO_x mixed oxides on SBA-15. The catalytic activity results were discussed in terms of loading and metal dispersion on the support material.

Keywords: Vanadium oxide; Titanium oxide; SBA-15; SCR; NO

Catalytic cracking of catechols and hydroquinones in the presence of nano-particle iron oxide by Eun-Jae Shin; Donald E. Miser; W. Geoffrey Chan; Mohammad R. Hajaligol (pp. 79-89).

Nano-particle “iron oxide�? was found to be an effective catalyst for the pyrolytic conversion of phenolic and other environmentally harmful aromatic compounds evolved during the combustion and pyrolysis of biomass. Catalytic cracking and oxidation of catechol, 3-methylcatechol, hydroquinone, 2-methylhydroquinone, and 2,3-dimethylhydroquinone over the temperature range of 180–430°C and under partially oxidative conditions were studied using nano-particle “iron oxide�?. We employed a flow tube reactor set-up for catalytic reactions, a molecular beam mass spectrometer for the real time sampling and measurement of products, and factor analysis to deconvolute the complex chemistry. High-resolution transmission electron microscopy (HRTEM) and surface area analyses by Braun-Emmet-Teller (BET) N₂ adsorption of the “iron oxide�? revealed that when preheated at the reaction temperatures, the iron hydroxide starting material dehydrated, partially converted to α-Fe₂O₃, and coarsened to the extent that it gave a lower BET surface area and larger particle sizes than that of the starting material. However, there were no further observed phase changes by HRTEM after the experiments and no carbon deposition was observed. BET surface areas of the preheated iron oxide measured at 200 and 350°C were 170 and 140m²/g, respectively. Experimentally derived activation energy for the decomposition of catechol over the nano-particle iron oxide was 15.5kcal/mol, which is a factor of about 2 lower than that for homogeneous decomposition. The oxidative decomposition of hydroquinone over the iron oxide required an activation energy of 10kcal/mol. While catechol and hydroquinone are thermally stable, the presence of the iron oxide and oxygen enhances their decomposition significantly at temperatures as low as 260°C for catechol and 180°C for hydroquinone. Less toxic products were favorably formed over the iron oxide. Reaction pathways of cracking products from each phenolic compound in the presence of the iron oxide could be summarized as follows: each starting material (primary products) converted to the corresponding quinones with two subsequent stepwise CO expulsions (secondary products) and all these products eventually were converted to carbon dioxide, water and some carbon monoxide (tertiary products).

Keywords: Catechol; Hydroquinone; Cracking; Catalysis; Molecular beam mass spectrometer; Nano-particle iron oxide

Measurement of benzene, toluene, ethylbenzene and o-xylene gas phase photodegradation by titanium dioxide dispersed in cementitious materials using a mixed flow reactor by A. Strini; S. Cassese; L. Schiavi (pp. 90-97).

A method for the measurement of the photocatalytic activity of titanium dioxide dispersed in cementitious building materials was developed as part of the European Project Photocatalytic Innovative Coverings Applications for Depollution Assessment (PICADA). The method is based on a specially designed stirred flow reactor. It is aimed at the measuring of the photodegradation of organic compounds in air at ppb level at the surface of photocatalytic materials. The use of an actively mixed flow reactor results in a uniform concentration of reactants at the catalytic material surface at high conversion factors which also allows to measure the photocatalytic activity bypassing the limitations imposed by the concentration gradients of unmixed flow reactors. A titanium dioxide modified cementitious material was studied by applying the described method, with a benzene, toluene, ethylbenzene and o-xylene (BTEX) mixture used as organic pollutant standard. The pollutant concentrations and irradiation levels used throughout the study were comparable to those that can be found under real ambient conditions. The effects of variation of pollutant concentration, irradiation level and titanium dioxide percentage in the cementitious materials were studied. The photocatalytic activity of a pure titanium dioxide film was also measured to stand as reference benchmark. The cementitious photocatalytic material showed an interesting photocatalytic activity with linear dependence versus pollutant air concentration and irradiance. On the other hand the variation of titanium dioxide content (from 0 to 5.6% as dry powder) in the cementitious mixture showed a non-linear relationship denoting a relative loss of efficiency at higher concentrations.

Keywords: Mixed photocatalytic flow reactor; Photocatalytic materials; Photocatalysis; TiO; ₂; Building materials; BTEX; Air pollution; Depollution; PICADA project

Dynamic behaviour of activated carbon catalysts during ozone decomposition at room temperature by Challapalli Subrahmanyam; Dmitri A. Bulushev; Lioubov Kiwi-Minsker (pp. 98-106).

The catalytic decomposition of ozone (200–1600ppm) to molecular oxygen was investigated over activated carbons in the form of woven fibre fabrics (ACF) or granules (ACG) at room temperature. The dynamics of carbon activity was characterised by two distinct regions. First the “high activity�? towards ozone decomposition was observed, which was mainly due to chemical interaction of ozone with carbon. This interaction resulted in the formation of oxygen containing surface groups on carbon until saturation. Then the conversion was sharply decreased and carbons went to “low activity�? region. The ozone decomposition to molecular oxygen takes place in this region following a catalytic route. The carbon activity in dry atmosphere was compared with the activity in the presence of water vapour and NO_x. Water vapour diminished the catalytic activity, but in the presence of NO_x carbons were observed to be more active due to the change in the C-surface functionality. The surface functional groups were modified in two ways: by boiling in diluted HNO₃ or by thermal treatment in He at temperatures up to 1273K. The acid pre-treatment was found to increase the activity of carbons under the quasi steady-state, while the thermal treatment at 1273K renders catalysts with lower activity. The ozone decomposition toward gasification of carbon producing CO_x took place with the selectivity less then 25%. The catalysts were characterised by temperature-programmed decomposition of surface functional groups, X-ray photo-electron and IR-spectroscopy. Mechanistic aspects of the reaction are discussed.

Keywords: Activated carbon; Ozone decomposition; Surface functional groups; Structured fibre catalyst; Gasification of carbon; Temperature-programmed decomposition; XPS; FT-IR

In situ DRIFTS study of the selective reduction of NO_x with alcohols over Ag/Al₂O₃ catalyst: Role of surface enolic species by Qiang Wu; Hong He; Yunbo Yu (pp. 107-113).

In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to clarify the formation and reactivity of enolic species and its role in the formation of the isocyanate species (–NCO) during the selective catalytic reduction of NO_x (SCR of NO_x) by alcohols (CH₃OH, C₂H₅OH and isopropyl alcohol (IPA)) over Ag/Al₂O₃ catalyst. The enolic species, which was derived from the partial oxidation of C₂H₅OH and IPA in the presence of O₂ over Ag/Al₂O_3, had a high reactivity with NO+O_2, resulting in a high surface concentration of –NCO species and high efficiency of NO_x reduction when using C₂H₅OH or IPA as reductants. In contrast, CH₃OH was much less effective for the SCR of NO_x. The order of the facility for the formation of enolic species and –NCO species was in good agreement with the order of the activities in the SCR of NO_x process (C₂H₅OH>IPA>CH₃OH) in the moderate temperature range of 523–623K.

Keywords: In situ DRIFTS; Ag/Al; ₂; O; ₃; Selective catalytic reduction; Enolic species; Isocyanate species (–NCO)

Synthesis and characterization of manganese oxides employed in VOCs abatement by Luciano Lamaita; Miguel A. Peluso; Jorge E. Sambeth; Horacio J. Thomas (pp. 114-119).

Two MnO₂ were prepared by different methods: (i) MnCO₃ decomposition; and (ii) oxidation of acid MnSO₄ solution. The combined use of X-ray diffraction (XRD), DRIFTS, DRS–UV–vis and TGA techniques revealed: (i) the presence of Mn⁴⁺–Mn³⁺; (ii) a poor crystallinity; and (iii) OH species at temperatures higher than 200°C.The catalysts were tested in the complete oxidation of ethanol to carbon dioxide and water, and the reaction results showed that the catalytic activity of both samples were larger than MnO₂ (pyrolusite, β-MnO₂) and Mn₂O₃ (like bixbyite) oxides. The high activity of the prepared oxides can be related to the simultaneous presence of Mn³⁺ and Mn⁴⁺ ions and OH⁻ species generated by Mn⁴⁺ vacancies. In addition, in situ DRIFT spectroscopy demonstrated a different mechanism of adsorption-reaction of ethanol between the two synthesized manganese oxides.

Keywords: γ-MnO; ₂; nsutite; Manganese oxides; DRIFTS; Ethanol oxidation; VOCs

Differential kinetic analysis of diesel particulate matter (soot) oxidation by oxygen using a step–response technique by Aleksey Yezerets; Neal W. Currier; Do Heui Kim; Heather A. Eadler; William S. Epling; Charles H.F. Peden (pp. 120-129).

The effects of a catalytic coating on the oxidation of captured soot over diesel particulate filters (DPF) is debated in the literature, since a catalyzed filter wall appears to lack sufficiently tight contact with soot deposits to exercise direct catalytic action. The topology of soot–catalyst contact may change with progressive oxidation of the soot layer; hence, a technique capable of probing catalytic action via detailed kinetic analysis at different stages of oxidation is required to conclusively resolve this problem. A novel step–response technique was developed in this work as a methodological foundation for such study. Using this technique, various aspects of the oxidation process can be probed while consuming only differential amounts of carbon, and the impact of the reaction heat on the measured rates can be minimized. This technique was applied to soot oxidation by O₂ and showed that, after decoupling effects due to the sample history, carbon oxidation by O₂ in the absence of H₂O can be well-described by an unmodified Arrhenius equation, with similar activation energy values for diesel and model soot samples (137±8.7 and 132±5.1kJ/mol, respectively). The reaction order in O₂ for these samples was found to be 0.61±0.03 and 0.71±0.03, respectively, and was remarkably independent of the temperature, suggesting that the fractional order is not due to mixed kinetic control. The reaction mechanism was also found to be independent of carbon conversion. The density of the reaction sites, however, appeared to increase with oxidation. This increase could not be accounted for by the changes in the specific surface area, either directly measured or derived from such simplified models as the shrinking-core formalism. The entire set of obtained experimental results can be described using a kinetically uncomplicated model in a broad range of temperatures, partial pressures of oxygen and degrees of soot oxidation.

Keywords: Diesel particulate matter; Soot; Carbon oxidation; Experimental methodology; Reaction kinetics

Steam reforming of model compounds and fast pyrolysis bio-oil on supported noble metal catalysts by Cyrille Rioche; Shrikant Kulkarni; Frederic C. Meunier; John P. Breen; Robbie Burch (pp. 130-139).

The production of hydrogen by steam reforming of bio-oils obtained from the fast pyrolysis of biomass requires the development of efficient catalysts able to cope with the complex chemical nature of the reactant. The present work focuses on the use of noble metal-based catalysts for the steam reforming of a few model compounds and that of an actual bio-oil. The steam reforming of the model compounds was investigated in the temperature range 650–950°C over Pt, Pd and Rh supported on alumina and a ceria–zirconia sample. The model compounds used were acetic acid, phenol, acetone and ethanol. The nature of the support appeared to play a significant role in the activity of these catalysts. The use of ceria–zirconia, a redox mixed oxide, lead to higher H₂ yields as compared to the case of the alumina-supported catalysts. The supported Rh and Pt catalysts were the most active for the steam reforming of these compounds, while Pd-based catalysts poorly performed. The activity of the promising Pt and Rh catalysts was also investigated for the steam reforming of a bio-oil obtained from beech wood fast pyrolysis. Temperatures close to, or higher than, 800°C were required to achieve significant conversions to CO_x and H₂ (e.g., H₂ yields around 70%). The ceria–zirconia materials showed a higher activity than the corresponding alumina samples. A Pt/ceria–zirconia sample used for over 9h showed essentially constant activity, while extensive carbonaceous deposits were observed on the quartz reactor walls from early time on stream. In the present case, no benefit was observed by adding a small amount of O₂ to the steam/bio-oil feed (auto-thermal reforming, ATR), probably partly due to the already high concentration of oxygen in the bio-oil composition.

Keywords: Steam reforming; Bio-oil; Acetic acid; Acetone; Ethanol; Phenol; Ceria; Zirconia; Alumina; Pt; Pd; Rh; Auto-thermal reforming

Visible light mediated photocatalytic degradation of gaseous trichloroethylene and dimethyl sulfide on modified titanium dioxide by Kristof Demeestere; Jo Dewulf; Teruhisa Ohno; Pepe Herrera Salgado; Herman Van Langenhove (pp. 140-149).

This paper reports the potential of four modified TiO₂ photocatalysts to degrade gaseous volatile organic compounds under visible light irradiation. Two modified photocatalysts were prepared by sensitizing TiO₂ Degussa P25 with CdS and eosin Y, respectively. Two other photocatalysts were S-doped TiO₂. One was prepared through a recently described sol–gel method (S-doped TiO₂-SG), whereas a new type was synthesized by a physical mixture method (S-doped TiO₂-PM).All modified photocatalysts showed a shift in UV–vis absorbance towards higher wavelengths, up to λ=620nm. Photocatalytic activity under near-UV and visible light irradiation was systematically investigated through the degradation of gaseous trichloroethylene (TCE) and dimethyl sulfide (DMS) in a batch reactor. Although TiO₂ Degussa P25 showed 1.3–6.6 times higher TCE degradation rates than modified photocatalysts under near-UV irradiation, no significant activity was observed at λ>400nm. In contrast, modified catalysts showed photocatalytic activity under both blue (400–540nm) and yellow light (480–720nm) irradiation, with S-doped TiO₂-PM and S-doped TiO₂-SG giving the highest TCE degradation rates, respectively. Under daylight irradiation (400–720nm), S-doped TiO₂-PM yielded the highest activity towards both TCE and DMS degradation, exemplified by removal efficiencies higher than 99% within 110min of irradiation at concentrations up to 537ppmv.

Keywords: Photocatalysis; Titanium dioxide; Visible light; Sensitizing; Sulfur doping; Volatile organic compounds; Trichloroethylene; Dimethyl sulfide; Gas-phase

Kinetic analysis of non-catalytic and Mn-catalysed combustion of diesel soot surrogates by R. L�pez-Fonseca; U. Elizundia; I. Landa; M.A. Guti�rrez-Ortiz; J.R. Gonz�lez-Velasco (pp. 150-158).

The kinetics of the combustion process of two carbon blacks, selected as diesel soot surrogates, namely, Flammruss 101 and Printex XE-2B, was investigated by dynamic thermogravimetry in an excess of air. The kinetic parameters (activation energy and pre-exponential factor) were accurately calculated by different processing methods, such as Kissinger–Akahira–Sunose isoconversional method and Coats-Redfern model-fitting method. Manganese (as manganese oxide) added to diesel soot surrogates, strongly decreased the ignition temperatures by 150–200°C. The activation energy of the catalytic process was lowered by about 15 and 10kJmol⁻¹ for Flammruss 101 and Printex XE-2B sample, respectively, with respect to the non-catalytic oxidation. The effectiveness of carbon–catalyst contact appeared to strongly affect the catalytic performance. Thermal experiments confirmed that, on one hand, impregnation markedly increased the reactivity in comparison with a simple physical mixture, and on the other hand, a highly porous structure of the parent carbon material enhanced the catalytic role of the active phase.

Keywords: Diesel soot; Kinetics; Combustion; Manganese additives; Dynamic thermogravimetry

Photocatalytic degradation of hydrogen sulfide and in situ FT-IR analysis of reaction products on surface of TiO₂ by Sho Kataoka; Enkyu Lee; M. Isabel Tejedor-Tejedor; Marc A. Anderson (pp. 159-163).

The photocatalytic oxidation of hydrogen sulfide at the gas/solid interface was investigated using TiO₂ as the photocatalyst. A malodorous compound, hydrogen sulfide was removed via a photocatalytic process under ambient conditions. Hydrogen sulfide was oxidized to sulfate species on the surface of TiO₂ without producing a noticeable gaseous intermediate, e.g., sulfur dioxide. The formation of sulfate species was confirmed by X-ray photoelectron spectroscopy (XPS). The surface chemistry of this photocatalytic oxidation was probed using two different types of in situ infrared (IR) spectroscopy techniques: diffuse reflectance IR spectroscopy (DRIFTS), and thin-film transmission IR spectroscopy. From the results obtained from DRIFT analysis, sulfate ions were accumulating proportionally with time on the surface of the catalyst during the course of the photocatalytic reaction. From further information gleaned from the transmission IR spectra (detected peaks at 1093 and 996cm⁻¹), SO₂⁻ may be one of the predominant intermediates that appear over the time of this reaction. Although these results do not reveal the entire reaction pathway of the conversion of sulfides to sulfates, our results using these in situ FT-IR techniques have been valuable in confirming that the photocatalytic oxidation of hydrogen sulfide occurs on the surface of particulate TiO₂.

Keywords: Photocatalytic; Hydrogen sulfide; Infrared spectroscopy; TiO; ₂

Thermal decomposition of dispersed and bulk-like NO_x species in model NO_x trap materials by Xiaoyin Chen; Johannes Schwank; John Li; William F. Schneider; Christian T. Goralski Jr.; Peter J. Schmitz (pp. 164-175).

The thermal decomposition of bulk Ba(NO₃)₂, Ba(NO₃)₂ impregnated on γ-Al₂O₃, and the release of NO₂ stored on BaO/γ-Al₂O₃ are investigated by thermogravimetric analysis (TGA) and infrared spectroscopy (IR) as a function of baria loading. Two distinct weight loss events at ∼434°C and ≥545°C are observed on the γ-Al₂O₃ supported samples, corresponding to the decomposition of dispersed and bulk-like Ba(NO₃)₂ to BaO, respectively. Decomposition of dispersed phase having a temperature of 150°C lower than bulk Ba(NO₃)₂ is attributed to a strong interaction between dispersed BaO and alumina. Bulk-like phase shows a similar decomposition characteristics to bulk Ba(NO₃)₂ as BaO loading increases to 31.8%. The decomposition products vary from predominantly NO₂ at low temperature (≤434°C) to NO at high temperature (≥545°C), consistent with the trend expected from the NO₂↔NO+1/2O₂ thermal equilibrium. As the total baria loading is increased, the amount of dispersed phase saturates at a baria loading of 14% (w/w) while the bulk-like phase increases without reaching saturation. Both phases can be regenerated on 15min exposure of corresponding BaO/Al₂O₃ to NO₂ at room temperature. The release of these regenerated nitrates mimics the decomposition characteristics of impregnated Ba(NO₃)₂ on γ-Al₂O₃. X-ray powder diffraction and IR spectra show that the stored NO₂ species gradually convert to a crystalline, bulk-like Ba(NO₃)₂ phase when aged at room temperature. These results are useful for optimizing BaO loading strategies for lean NO_x trap catalyst.

Keywords: Lean NO; _x; trap; Thermogravimetry; Ba(NO; ₃; ); ₂; BaO; Dispersion; Decomposition; NO; ₂; storage

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Applied Catalysis B, Environmental (v.61, #1-2)