Diesel engines when compared with gasoline engines produce higher amount of NOx due the operating conditions. Among the NOx produced NO represents the great majority while, under air excess conditions, the removal of NOx is necessarily catalytic and still challenging. In the ammonia based SCR, it is often admitted that, when dealing with the original formulation developed for stationary sources (V/TiO2), the fast SCR proceeds in presence of an equimolar mixture of NO and NO2. Most of the catalytic formulations developed up to now (except Cu based zeolites) thus suffer the same rate determining step consisting in the NO to NO2 oxidation. Aiming at improving the catalytic efficiency through the catalyst composition, it is fundamental to understand the reaction mechanism at its elementary steps in order to properly design the active sites. The choice regarding the distinct possible hypothetical mechanisms was thus here guided by the nature of the active sites. It is indeed worth knowing, for a better tuning of the catalyst formulation, whether isolated, oligomeric or dual iron sites are involved in the catalytic loop. The approach in this work consists in a systematic study of the influence of the inlet NO concentration under O-2 excess on both the initial reaction rate (NO to NO2 conversion level kept below 10%) and the NO coverage level onto iron measured by operando FTIR. Isothermal experiments were performed over an aged FeFER catalyst at three distinct temperatures. The whole set of data was then processed and compared to the expected evolution derived from five possible mechanisms. The best mechanism determined in the frame of this study involves isolated iron sites onto which NO and O-2 co-adsorb and the corresponding rate determining step consists in the dissociation of the so-formed Fe_NOO2 intermediate species. The associated activation energy and reaction enthalpy values are then evaluated.

The thin-layer cascade (TLC) system is an open system for microalgae cultivation composed of a retention tank connected by pump and pipes to a horizontal exposed area that consists of an upper basin and a TLC. Light and hydrodynamics are different among compartments, so overall photosynthetic activity can be influenced by the retention time of the cells in each compartment. We established 2 settings with different retention times in the cascade and tank to compare the photosynthetic activity of Chlorella fusca (Chlorophyta) among compartments. Changes in the retention time were achieved using 2 layer thicknesses in the cascade: 8 and 18 mm. Retention time in the cascade represented about 16 and 34% of the duration of a whole system cycle when H1 (8 mm thickness) and H2 (18 mm thickness) units, respectively, were used. These retention periods were lower than those in the tank (67 and 49%, respectively) but higher than those in the basin (12% for both H1 and H2). Photosynthetic activity was measured in situ as relative electron transport rate (rETR) using a pulse-amplitude modulated fluorometer. In both setups, the highest rETR was reached in the cascade. The increase of the layer thickness was a good option to avoid photoinhibition. We suggest estimating the mean rETR of the whole system considering the retention time, since it can better reflect overall growth because it takes into account the time that the cells spend in each compartment. These results are useful for optimization of photosynthetic activity and growth of outdoor microalgae mass cultures in TLCs for biotechnological purposes.

This study assessed the interactive effects of UVR and nutrient depletion on Chlorella fusca cultures on the production and accumulation of particular biomolecules. To accomplish this, algae were grown for 5 d in outdoor thin-layer cascade cultivators under 3 nutrient treatments (full nutrients, -N and -S) and then transferred to outdoor cylindrical photobiore-actors for another 5 d. Cultures were then exposed to full solar radiation (PAB) and decreased UVR. During the last 5 d, bio-optical properties, photosynthetic activity, pigments, biochemical composition and oxidative stress were assessed. Initially, nutrient depletion caused changes in productivity and cell number in a manner that affected biochemical composition. After 3 d, the percentage of lipids in the cultures under N deprivation reached values appropriate for being used as feed or food additives or for energy applications (35% of lipid content), regardless of the light conditions. A longer exposure (5 d) resulted in interactive effects of light and nutrient conditions. Specifically, PAB increased lipid content in all cases (1.3- to 2.3-fold), but particularly under S deprivation. Longer exposure to PAB also increased oxidative stress in UVR and nutrient-limited treatments (-N and -S). These results showed that the benefits expected from nutrient depletion (increase in biomolecule content e.g. lipids, carbohydrates and pigments) were modulated by the negative effects of algal UVR acclimation costs.

Chlorella spp. are robust chlorophyte microalgal species frequently used in mass culture. The pH optimum for growth is close to neutrality; at this pH, theoretically little energy is required to maintain homeostasis. In the present study, we grew Chlorella fusca cells in an open, outdoor, thin-layer cascade photobioreactor (TLC), under ambient photon flux at the theoretically preferred pH (7.2), and let the culture pass the exponential growth phase. Using pH drift experiments, we show that an alkalization to pH 9 supported photosynthesis in the TLC. The increased photosynthetic activity under alkaline conditions was a pH-dependent effect, and not a dissolved inorganic carbon (DIC) concentration- or light intensity-dependent effect. Re-acidification (in one step or in increments) lowered gross oxygen production and increased non-photochemical quenching in short-term experiments. Gross oxygen production and electron transport rates in PSII were uncoupled during the pH perturbation experiments. Electron transport rates were only marginally affected by pH, whereas oxygen production rates decreased with acidification. Alternative electron pathways, electron donation at the plastid terminal oxidase and state-transitions are discussed as a potential explanation. Because cell material from the TLC was not operating at maximal capacity, we propose that alkalization can support photosynthesis in challenged TLC systems.

A commercial zeolite-based catalyst for NOx removal via ammonia SCR was studied with either pure NO or pure NO2 (as NOx compounds). The SCR efficiency was greatly enhanced when using pure NO2. The CO conversion levels enabled to illustrate that NO2 favours the CO oxidation into CO2, while NO formed would participate in the fast SCR path (like a ‘masked’ fast SCR process). The formation of NH4NO3 at low temperature, when using pure NO2, and its deposit onto the catalyst was evidenced by mean of the IR operando methodology. Its accumulation leads to a loss of activity for the NOx reduction, which must certainly be associated to an obstruction of the microporous system. Nevertheless, after a single thermal regeneration of the catalyst (which would arise during the catalyst ‘real life’ upon any increase of the engine regime), the SCR efficiency was fully recovered.

A commercial zeolite-based catalyst for NOx removal via ammonia SCR has been studied in a synthetic flow very close to a real automotive exhaust mixture. Particular attention has been paid to reproduce effective temperatures and space velocities. The impact of the hydrocarbon presence towards the NH3-SCR efficiency has been investigated through the use of a mixture of representative hydrocarbons, i.e. propene, toluene and decane. It has been found that both decane and toluene produce a carbonaceous deposit, partially hindering the reaction by pore blocking. However, it also appears that decane is the most inhibiting compound for the deNOx activity due to a competitive adsorption with ammonia on the active sites, notably at low temperature.

CO2 reforming of methane has been studied over Pt/Al2O3 model catalysts in a temperature range of 600–800 °C using steady-state and transient methods (Transient Response Method (TRM) and DRIFT-MS). Pt-supported catalysts were prepared using two different alumina (γ-Al2O3(S) Sasol-Puralox and a synthesized γ-Al2O3(N) with nanofibrous structure). Catalysts and supports were characterized by conventional methods (XRD, TEM, ABET, XPS) before and after reaction. Pt0 species are present in the catalysts, with a higher relative contribution for the catalyst that has a nanostructured support. Pt/γ-Al2O3(N) catalyst presented the best performance in reactivity and showed a low rate of carbon formation and a minimal water production. From TRM and DRIFT-MS results it can be concluded that, when CO2 and CH4 are fed separately into the reaction system, they are activated over the catalytic surface. Besides, when both reactants are fed contemporaneously the presence of CHX species promotes the CO2 activation that is responsible for the reforming reaction.

Iron was introduced by ionic exchange inside the FER structure in order to yield a Fe-FER series with increasing metal loading. Characterization of the Fe2+ cations by adsorption of CO at liquid nitrogen temperature followed by infrared spectroscopy allowed to identify three distinct sites for iron. The most abundant iron species are located on easily accessible sites of the FER structure, whereas high metal loading is required to observe more confined Fe2+ species. According to the CO adsorption results, the main iron species appears to be coordinatively unsaturated whereas isotopic labelling upon NO adsorption indicates that two distinct iron sites almost give rise to the same mononitrosyl infrared signature. Studying the catalyst upon interaction with NO and O2 in operando conditions leads to the observation of these mononitrosyl species who behave as reaction intermediates for the NO oxidation into NO2. All our Fe-FER samples presenting these mononitrosyl complexes are active not only in NO-to-NO2 reaction but also in the NOx selective catalytic reduction with ammonia. The effects of both NH3 and SO2 as adsorption competitor during the low temperature NH3-SCR are also discussed.

The effect of Te addition over Mo-V-O catalysts supported on alumina is discussed for the ammoxidation of propane to acrylonitrile. Catalysts were characterized before and after catalytic reaction by XPS, XRD, UV–vis and in situ Raman spectroscopies. The absence of Te in catalysts formulation and the presence of a high amount of vanadium induce the presence of V5+ species and the formation of V2O5 oxide; associated with a decrease in acrylonitrile selectivity. The presence of heteropolyacids-type structures, such as Al-Mo-V-O or Al-Mo-O, promotes a decreasing of the selectivity to acrylonitrile. The characterization results reveal that the surface of Mo-V-Te-O catalysts is further different from the binary counterparts, due to the presence of stabilized and reduced structures dispersed on the support. The Te incorporation to supported Mo-V catalysts conduces to a better performance during propane ammoxidation.

A series of polymeric carbon-coated monoliths oxidized with either concentrated or 2N HNO3, H2O2 or H2SO4 and subsequently loaded with 3wt.% vanadium were prepared. The influence of the different oxidation treatment conditions on the SCR (selective catalytic reduction) catalytic activity, texture and chemical surface properties were studied. Similar pore distribution and pore volumes were observed for the four oxidized samples, indicating that surface modification of carbon supports has been successfully made without disrupting the original textural structures of activated coated monoliths. The surface chemistry created by the oxidation treatments has two effects on the catalytic activity. One of these is that higher surface acidity results in higher NO reduction up to a certain extent. The highest acidities seem to promote a sufficiently strong NH3 adsorption on the surface such that the lack of efficient desorption decreases the overall NO conversion efficiency. The other effect is that a low surface acidity does not seem to promote vanadium dispersion and fixation, thereby also resulting in decreased NO reduction efficiency.

The effect of tungsten over Mo–V–O-based catalysts is evaluated. Alumina-supported Mo–V–W–O samples were prepared with different overall metal loading coverages, considering several relative metal atomic ratios; a bulk sample was also synthesized. The catalysts were characterized with BET, XRD, XPS and UV–vis. Mechanistic aspects of the light hydrocarbon oxidation were studied by the operando Raman-GC approach. Different surface structures were found and the better propylene yields were achieved when Mo–W and V–W were predominant structures. W incorporation to alumina-supported Mo–V catalysts yields better performance for propane ODH.

A FTIR “home-made” cell is used to study the evolution of surface species and gas phase coupled with a mass-spectrometer (MS) for time-resolved analysis in static and dynamic conditions in order to gain further information about the variables that influence the mechanism of reduction of NOx stored. A preliminary IR study with simultaneous gas and surface spectra of Pt-Ba-Al2O3 and free-Pt catalysts implies that the platinum is necessary for the regeneration in the appropriate temperature range (200–400°C). The use of different reducing gases (H2, C3H6 or C3H8) shows that the distribution of reduction products and the temperature reaction window are correlated with the reducing molecule. Secondly, an operando MS-FTIR technique permits us to compare a Pt-Ba-Al2O3 and Pt-K-Al2O3 catalysts under flow conditions during a complete NSR cycle, showing that barium containing catalyst allows better NSR performance.

The effect of tungsten incorporation in the surface composition and its catalytic performance is evaluated for alumina supported Mo-V-O, MoW-O, V-W-O and Mo-V-W-O nanostructurated-oxide catalysts. The characterization results reveal that the surface of Mo-V-W-O catalysts is further different from the binary counterparts, due to the presence of stabilized and reduced structures dispersed on the support. Such species are not present in the Mo-V-O catalysts; indicative that tungsten acts as a structural–chemical promoter. The in situ FT-IR study of these catalysts under propane + oxygen atmosphere showed that Mo-V-W-O catalyst is able to thermally activate the propane oxotransformation and ODH-products are registered in the gas-phase whereas oxygenate-compounds are detected on the surface of catalysts. # 2006 Elsevier B.V. All rights reserved.