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The role of two catalysts Pt/Al 2 O 3 and Ru/NaY on the oxidation of carbon by NO 2 was investigated in the temperature range 300–400 °C. In the case of Pt/Al 2 O 3 no significant catalytic effect on the carbon oxidation rate is observed although decomposition of NO 2 takes place on the noble metal and leads to the formation of NO. This result suggests that the amount of the oxygen atoms transferred from the metallic surface sites to the carbon surface to form C(O) complex is negligible. In contrast, in presence of Ru/NaY the oxidation rate of carbon by NO 2 is markedly increased. Hence, a significant part of the formed O through catalytic decomposition of NO 2 on Ru surface sites is transferred to the carbon surface leading to a larger amount of C(O) complexes on the carbon surface. Thus, the ruthenium surface is a generator of active oxygen species that are spilled over on the carbon surface at 350 °C.

International audience; Despite the huge literature on biomass char gasification with CO2 or H2O, ambiguity still hovers over the issue of char gasification in complex atmospheres. Gas alternation gasification experiments, in which the reacting gas is changed during the reaction, were performed with CO2/H2O at 900 degrees C for small (200 mu m) and large (13 mm) Low Heating Rate (LHR) beech wood char particles to assess the potential influences that CO2 and H2O can have on each other during the char gasification reaction. The results showed no influence of a first gasification atmosphere on the char reactivity under the second one. The char reactivity to a specific gas at a certain conversion level was the same as if the gasification reaction was operated from the beginning with the same atmosphere composition. The purpose of this paper is to bring understanding keys to this lack of influence of previous gasification conditions on the char reactivity. Characterization of the chars throughout the conversion by measuring the total surface area and the active surface area was first performed. Then a transport limitation analysis based on the Thiele modulus was considered. It was concluded that the two gasses develop different porosities in the char, however, the Thiele modeling results and active surface area analysis indicate respectively that gasses diffuse preferentially in large macro-pores and that the concentration of active sites evolves similarly during both gasification reactions. This similarity in the diffusion mechanism as well as in the evolution of the concentration of active sites could be a plausible explanation for the only-dependent conversion reactivity observed in the gas alternation gasification experiments.

International audience; Activated carbon was prepared from olive stones by physical activation using water vapor at 750°C. Textural, morphology and surface chemistry characterizations were achieved (nitrogen adsorption, SEM, FTIR and TPD–MS). NO2 adsorption was performed for different inlet gas compositions and temperatures. NO2 may adsorb directly on the oxygenated surface groups, and can also be reduced to NO. Therefore, a second NO2 molecule adsorbs on the oxygen left on the carbon surface. TPD performed after NO2 adsorption showed the presence of various surface groups. The adsorption capacity was about 131mg/g, which is higher than with several activated carbon prepared from classical lignocellulosic biomass. NO2 reduction into NO decreased with increasing the inlet oxygen concentration. In contrast, a slight decrease in the NO2 adsorption capacity was observed with increasing temperature. It seems that the activated carbons prepared from olive stones by steam activation could be used as efficient adsorbents for NO2 removal.

The oxidation mechanism of carbon by automotive exhaust gasses (O 2 , H 2 O and NO 2 ) was investigated in the range of temperature (300–400 °C) corresponding to the operation conditions of the continuous regeneration regime of the soot trap. No carbon gasification occurs when O 2 is injected in absence of NO 2 below 450 °C. However, when O 2 (10 vol.%) and NO 2 (100–600 ppmv) are both present in the gas mixture, two distinct carbon oxidation reactions take place. A direct reaction occurs between NO 2 and the carbon surface along with a co-operative one involving simultaneously O 2 and NO 2 . In the latter case, NO 2 promotes the decomposition of the intermediate C(O) complex. Injection of water vapour increases the overall oxidation rate but does not modify the global mechanism. The promoting effect of water is attributed to the intermediate formation of traces of nitric and nitrous acids which enhance the direct reaction C–NO 2 rate. In contrast, water has no measurable effect on the co-operative C–NO 2 –O 2 reaction. A relationship between the water promoting effect on the direct oxidation rate and the amount of theoretical formation of HNO 2 and HNO 3 was established.

Adsorption of NO2 on carbon black has been examined for different NO2 concentrations (400 or 600 ppm) and temperatures (50 or 100 °C). The influence of chemisorption of oxygen on the carbon surface at 300 °C before exposure to NO2 has been reported. Temperature programmed desorption (TPD) was performed after NO2 adsorption to identify the adsorbed species by measuring the amounts of evolved gases NO, NO2, CO and CO2. During the exposure of the carbon black to NO2, both adsorption and reduction of NO2 to NO has been observed. From the oxygen and nitrogen balance data, it is shown that the NO2 adsorption step leads to the formation of both oxygen and nitrogen surface complexes such as C(O) and C(ONO2). Based on the TPD results, a desorption process has been proposed. Chemisorption of oxygen before exposure to NO2 leads to an increase, during the adsorption step, of both nitrogen adsorbed and NO evolved species. This behaviour has been attributed to already existing oxygen complexes resulting from O2 chemisorption. In fact, NO2 adsorbs mainly on preexisting oxygen complexes. A relationship between the additional adsorbed NO2 during the adsorption step and the excess of CO2 released during the TPD below 500 °C has been established.

International audience; This work was devoted to study experimentally and numerically the oxygen carrier (NiO/NiAl2O4) performances for Chemical-Looping Combustion applications. Various kinetic models including Shrinking Core, Nucleation Growth and Modified Volumetric models were investigated in a one-dimensional approach to simulate the reactive mass transfer in a fixed bed reactor. The preliminary numerical results indicated that these models are unable to fit well the fuel breakthrough curves. Therefore, the oxygen carrier was characterized after several operations using Scanning Electronic Microscopy (SEM) coupled with equipped with an energy dispersive X-ray spectrometer (EDX). These analyses showed a layer rich in nickel on particle surface. Below this layer, to a depth of about 10 µm, the material was low in nickel, being the consequence of nickel migration. From these observations, two reactive sites were proposed relative to the layer rich in nickel (particle surface) and the bulk material, respectively. Then, a numerical model, taking into account of both reactive sites, was able to fit well fuel breakthrough curves for all the studied operating conditions. The extracted kinetic parameters showed that the fuel oxidation was fully controlled by the reaction and the effect of temperature was not significant in the tested operating conditions range

Biomass thermochemical conversion is complex and requires a good understanding of the thermal decomposition process. This process may be identified using mass loss kinetics which are useful for the design of proper equipment used for biomass conversion. This work aims to determine devolatilization kinetic parameters characterizing four Tunisian biomass species: industrial by product (Pine Sawdust), agro-industrial by product (Olive Solid Waste), agricultural residue (Date Palm Trunk) and seaweed (Posidonia Oceanica) using data from non-isothermal thermogravimetry and the Coats and Redfern calculation method. Decomposition TG and DTG data were analyzed by applying 10 kinetic models including processes governed by nuclei growth, surface nucleation followed by geometric, diffusion and chemical reaction models. Obtained results show that biomass pyrolysis is represented by two successive steps: (i) devolatilization stage characterized by high weight loss rate, which is well described by diffusional, surface nucleation followed by geometric and first order chemical reaction models. (ii) char formation stage characterized by low weight loss rate, which is well described by second order and third order chemical reaction models. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 1452–1458, 2014

International audience; Experimental studies on diesel soot oxidation under a wide range of conditions relevant for modern diesel engine exhaust and continuously regenerating particle trap were performed. Hence, reactivity tests were carried out in a fixed bed reactor for various temperatures and different concentrations of oxygen, NO2 and water (300–600 °C, 0–10% O2, 0–600 ppm NO2, 0–10% H2O). The soot oxidation rate was determined by measuring the concentration of CO and CO2 product gases. The parametric study shows that the overall oxidation process can be described by three parallel reactions: a direct C–NO2 reaction, a direct C–O2 reaction and a cooperative C–NO2–O2 reaction. C–NO2 and C–NO2–O2 are the main reactions for soot oxidation between 300 and 450 °C. Water vapour acts as a catalyst on the direct C–NO2 reaction. This catalytic effect decreases with the increase of temperature until 450 °C. Above 450 °C, the direct C–O2 reaction contributes to the global soot oxidation rate. Water vapour has also a catalytic effect on the direct C–O2 reaction between 450 °C and 600 °C. Above 600 °C, the direct C–O2 reaction is the only main reaction for soot oxidation. Taking into account the established reaction mechanism, a one-dimensional model of soot oxidation was proposed. The roles of NO2, O2 and H2O were considered and the kinetic constants were obtained. The suggested kinetic model may be useful for simulating the behaviour of a diesel particulate filter system during the regeneration process.

International audience; Applied Catalysis B: Environmental97 (2010) 13–20Contents lists available atScienceDirectApplied Catalysis B: Environmentaljournal homepage:www.elsevier.com/locate/apcatbModeling of NOxadsorption–desorption–reduction cycles on aruthenium loaded Na–Y zeoliteM. Labakia,1, M. Issab, S. Smeekensb, S. Heylenb, C.E.A. Kirschhockb,K. Villanib, M. Jeguirima, D. Habermachera, J.F. Brilhaca,∗, J.A. MartensbaLaboratoire Gestion des Risques et Environnement, Université de Haute-Alsace, 25 rue de Chemnitz, 68200 Mulhouse, FrancebCentrum voor Oppervlaktechemie en Katalyse, Katholieke Universiteit Leuven, Kasteel Arenberg, No. 23, 3001 Heverlee Leuven, Belgiumarticle infoArticle history:Received 18 December 2009Received in revised form 23 February 2010Accepted 1 March 2010Available online 6 March 2010Keywords:Ru/Na–YNOxstorage and reductionN2O3Kinetic modelingabstractAdsorption of NO from a gas stream containing oxygen and water and desorption and reduction usinga rich gas mixture were investigated in the temperature range 230–315◦C on Na–Y zeolite loaded with3wt.%ruthenium.TheNOxstoragecapacitywasfoundlittledependentontemperatureandwatercontentof the gas. The adsorption–desorption–reduction process was modeled using a one-dimensional fixed-bed model and assuming co-adsorption of NO and NO2molecules on Na–Y zeolite, ruthenium catalyzedNO into NO2oxidation by molecular oxygen during adsorption and ruthenium catalyzed NOxreductionby hydrogen during desorption. Kinetic constants were estimated through data fitting. An acceptableagreement between experimental and calculated values was obtained. NOxadsorption and desorptionkinetics on Na–Y zeolite with and without ruthenium were substantially different revealing that ruthe-nium besides catalyzing NOxoxidation and reduction had a drastic influence on the NOxadsorption sitesof Na–Y zeolite.

Olive oil mill wastewater (OMWW) generated by the olive oil extraction industry constitutes a major pollutant, causing a severe environmental threats because of the high chemical oxygen demand and the high content of polyphenol. This work studied a combined process of absorption on sawdust, a low-cost renewable absorbents, and an energetic valorisation via combustion was studied. The thermal behaviour of different OMWW/sawdust blends was studied under inert and oxidative atmosphere from 20 to 900 degrees C using thermogravimetric analysis (TGA). Gaseous emissions such as CO(2), CO and volatile organic compounds (VOCs) were measured under oxidative conditions at 600 degrees C in a fixed-bed reactor. Kinetic parameters were obtained and compared for the different mixtures of OMWW and sawdust. The absorption of the organic content of OMWW on sawdust improves the decomposition of cellulosic compounds at low temperatures in both atmospheres. Compared to sawdust, absorption of the organic content of OMWW on sawdust favours a combustion process with lower molar ratio of CO/CO(2) in the exhaust. Combustion of an impregnated sawdust containing 40 wt.% of the organic content of the OMWW generates the same amount of gas in the exhaust as sawdust. OMWW/sawdust blends may therefore be a promising biofuel with low environmental impacts.

In the current energy context, there is a need to develop the use of renewable energy sources, such as biomass. A promising way to produce energy from biomass is through gasification. However, some biomass species can be problematic during the gasification process due to their high inorganic content that can strongly influence the reaction kinetics. To date, the inorganic effects are known but the underlying mechanisms are still poorly understood. In this context, the objective of the present work was to contribute to the understanding of the inorganic elements role during the biomass steam gasification. In particular, the phenomena involving K and Si during the biomass steam gasification, especially through the gas phase, and with particular attention on their influence on the reaction kinetics were investigated. Investigations were conducted at an experimental level, with thermogravimetric analyses and physicochemical characterizations of the chars and ashes. They were supported by calculations at thermodynamic equilibrium as well as by literature review. The results have proven that the biomass inorganic composition is the main parameter explaining the differences between the gasification kinetic behaviors of the biomass species. From this conclusion, the specific effects of K and Si—two major inorganic elements in biomass—were further investigated in details. A competition was highlighted between two reactions involving K, most likely in the form of KOH(g): i) the catalysis of the steam gasification—whose mechanism starts from the pyrolysis step—on the one hand, and ii) the heterogeneous reaction between KOH(g) and SiO2 to form non-catalytic species on the other hand. Additionally, it was showed that increasing the biomass SiO2 content, whatever its crystalline form, slows its gasification down in a non-linear way and until a saturation effect., Dans le contexte énergétique actuel, l’utilisation de sources d’énergie renouvelables, telle que la biomasse, doit être développée. La gazéification est l’une des voies prometteuses de production d’énergie à partir de la biomasse. Cependant, certaines biomasses peuvent être problématiques lors de la gazéification à cause de leur taux élevé en éléments inorganiques qui peut fortement influencer la cinétique de la réaction. A ce jour, ces effets sont connus mais les mécanismes en jeu restent mal compris. Dans ce contexte, l’objectif de ce travail était de contribuer à la compréhension du rôle des éléments inorganiques au cours de la gazéification sous vapeur d’eau de la biomasse. En particulier, les recherches se sont concentrées sur les phénomènes impliquant K et Si au cours de la gazéification sous vapeur d’eau de la biomasse, notamment dans la phase gaz, et avec une attention particulière vis-à-vis de leur influence sur la cinétique de la réaction. Les résultats ont démontrés que la composition en éléments inorganiques de la biomasse est le paramètre principal permettant d’expliquer les différences entre les cinétiques de gazéification des différentes espèces de biomasse. A partir de cette conclusion, l’effet particulier de K et Si (deux des éléments inorganiques majeurs de la biomasse) a été étudié en détails. Une compétition a été mise en évidence entre deux réactions impliquant K, très probablement présent sous forme de KOH(g) : i) la catalyse de la gazéification, dont le mécanisme commence dès la pyrolyse, d’une part, et ii) la réaction hétérogène entre KOH(g) et SiO2 pour former des espèces non-catalytiques d’autre part. De plus, il a été montré qu’augmenter la concentration en SiO2, quelle que soit sa forme cristalline, de la biomasse ralentit sa gazéification de façon non-linéaire et jusqu’à une saturation.

International audience; Rapid development of the technologies based on electric energy in the last decades have stimulated intensive research on efficient power sources. Electrochemical energy conversion and storage systems are based on Faradaic reactions (charge transfer) and electrostatic attraction of ions at the electrode/electrolyte interface. The latter might be an interesting solution for applications requiring moderate energy density, high power rates, and long cycle life. Electrochemical capacitors (ECs) store the charge in a physical manner, hence, their energy density is moderate. At the same time, the lack of electrochemical reactions ensures very high power and long cycle life compared to batteries. Activated carbons with their versatile properties (like specific surface area, well-developed and suitable porosity, heteroatoms in the graphene matrix) are the most popular materials in EC application. This chapter provides a comprehensive overview of the carbon-based materials recently developed, with special attention devoted to those obtained by biomass carbonization and activation. Electrochemical properties demonstrated by such carbons are discussed in respect to their physicochemical characteristics

International audience; The continuous increase of energy demands based on fossil fuels in the last years have lead to an increase of greenhouse gases (GHG) emission which strongly contribute to global warming. The main strategies to limit this phenomenon are related to the efficient capture of these gases and to the development of renewable energies sources with limited environmental impact. Particularly, carbon dioxide (CO2) and methane (CH4) are the main constituents of greenhouse gases while hydrogen (H2) is considered an alternative clean energy source to fossil fuels. Therefore, tremendous research to store these gases has been reported by several approaches and among them the physisorption on activated carbons (AC) have received significant attention. Their abundance, low cost and tunable porous structure and chemical functionalities with an existing wide range of precursors that includes bio-wastes make them ideal candidates for gas applications. This chapter presents the recent developments on CH4, CO2 and H2 storage by activated carbons with focus on biomass as precursor materials. An analysis of the main carbon properties affecting the AC's adsorption capacity (i.e. specific surface area, pore size and surface chemistry) is discussed in detail herein.