9 research outputs found
COâ catalytic purification issued from oxyfuel-combustion
Le rĂ©chauffement climatique principalement dĂ» aux Ă©missions importantes de COâ, gaz Ă effet de serre de rĂ©fĂ©rence, encourage les chercheurs Ă trouver des solutions pour lutter contre ce phĂ©nomĂšne. Les techniques consistant Ă capter et stocker ou valoriser le COâ sont des solutions pertinentes, mais qui nĂ©cessitent d'avoir du COâ le plus pur possible. Parmi ces techniques, l'oxycombustion parait assez prometteuse pour produire du COâ en forte concentration. Toutefois, selon la nature du combustible et la puretĂ© de l'oxygĂšne, certains polluants peuvent apparaĂźtre tels que le CO et les NOx. Pour rĂ©aliser cette purification, la catalyse est un moyen efficace permettant de transformer simultanĂ©ment le NO et le CO respectivement en Nâ et COâ. L'objectif de cette Ă©tude est donc, de mettre au point des catalyseurs actifs pour la rĂ©duction des NOx en Nâ par le CO, dans un milieu oxydant et en prĂ©sence d'eau. Deux types de catalyseurs ont Ă©tĂ© choisis : les mĂ©taux nobles (Pd, Pt, Rh) supportĂ©s et les oxydes de mĂ©taux de transition (Co, Cu, Al). Les rĂ©sultats obtenus montrent que les catalyseurs Ă base de Pt sont plus performants et que leur activitĂ© catalytique augment pour les Ă©chantillons supportĂ©s sur un support neutre (SiOâ) ou rĂ©ductible (TiOâ) que ce soit en prĂ©sence ou en absence d'eau. Les oxydes mixtes de mĂ©taux de transition, obtenus par voie hydrotalcite, montre que la nature du cation bivalent joue un rĂŽle important. Les oxydes mixtes Co-Cu ont montrĂ© une meilleure activitĂ© que les matĂ©riaux composĂ©s d'un seul de ces deux Ă©lĂ©ments. Cependant, l'ajout d'eau dans le flux rĂ©actionnel conduit Ă une baisse d'activitĂ© des catalyseurs contenant du Cu.Global warming, mainly due to high COâ emissions, reference greenhouse gas, motivates researchers to find solutions to combat this phenomenon. The techniques of capturing and storing or reuse of COâ are revelant solutions, but which require a COâ as pure as possible. Among these techniques, oxyfuel combustion seems promising enough to produce COâ in high concentration. However, depending on the nature of the fuel and the oxygen purity, some pollutants may appear such as CO and NOx. To carry out this purification, catalysis is an effective means for simultaneously converting NO and CO respectively into Nâ and COâ. The objective of this study is to develop active catalysts for NOx reduction in Nâ by CO, in oxidizing conditions and presence of water. Two types of catalysts were chosen : supported noble metals (Pd, Pt, Rh) and transition metal oxides (Co, Cu, Al). The results obtained show that the Pt-based catalysts were more efficient and that their catalytic activity increases for the samples supported on a neutral support (SiOâ) or reducible (TiOâ) whether in the presence or absence of water. The mixed oxides of transition metals, obtained by hydrotalcite, show that the nature of the bivalent cation plays an important role. Co-Cu mixed oxides showed better activity than materials composed of only one of these two elements. However, the addition of water to the reaction flow led to a decrease in activity of the Cu-containing catalysts
Purification catalytique du COâ issu de l'oxycombustion
Global warming, mainly due to high COâ emissions, reference greenhouse gas, motivates researchers to find solutions to combat this phenomenon. The techniques of capturing and storing or reuse of COâ are revelant solutions, but which require a COâ as pure as possible. Among these techniques, oxyfuel combustion seems promising enough to produce COâ in high concentration. However, depending on the nature of the fuel and the oxygen purity, some pollutants may appear such as CO and NOx. To carry out this purification, catalysis is an effective means for simultaneously converting NO and CO respectively into Nâ and COâ. The objective of this study is to develop active catalysts for NOx reduction in Nâ by CO, in oxidizing conditions and presence of water. Two types of catalysts were chosen : supported noble metals (Pd, Pt, Rh) and transition metal oxides (Co, Cu, Al). The results obtained show that the Pt-based catalysts were more efficient and that their catalytic activity increases for the samples supported on a neutral support (SiOâ) or reducible (TiOâ) whether in the presence or absence of water. The mixed oxides of transition metals, obtained by hydrotalcite, show that the nature of the bivalent cation plays an important role. Co-Cu mixed oxides showed better activity than materials composed of only one of these two elements. However, the addition of water to the reaction flow led to a decrease in activity of the Cu-containing catalysts.Le rĂ©chauffement climatique principalement dĂ» aux Ă©missions importantes de COâ, gaz Ă effet de serre de rĂ©fĂ©rence, encourage les chercheurs Ă trouver des solutions pour lutter contre ce phĂ©nomĂšne. Les techniques consistant Ă capter et stocker ou valoriser le COâ sont des solutions pertinentes, mais qui nĂ©cessitent d'avoir du COâ le plus pur possible. Parmi ces techniques, l'oxycombustion parait assez prometteuse pour produire du COâ en forte concentration. Toutefois, selon la nature du combustible et la puretĂ© de l'oxygĂšne, certains polluants peuvent apparaĂźtre tels que le CO et les NOx. Pour rĂ©aliser cette purification, la catalyse est un moyen efficace permettant de transformer simultanĂ©ment le NO et le CO respectivement en Nâ et COâ. L'objectif de cette Ă©tude est donc, de mettre au point des catalyseurs actifs pour la rĂ©duction des NOx en Nâ par le CO, dans un milieu oxydant et en prĂ©sence d'eau. Deux types de catalyseurs ont Ă©tĂ© choisis : les mĂ©taux nobles (Pd, Pt, Rh) supportĂ©s et les oxydes de mĂ©taux de transition (Co, Cu, Al). Les rĂ©sultats obtenus montrent que les catalyseurs Ă base de Pt sont plus performants et que leur activitĂ© catalytique augment pour les Ă©chantillons supportĂ©s sur un support neutre (SiOâ) ou rĂ©ductible (TiOâ) que ce soit en prĂ©sence ou en absence d'eau. Les oxydes mixtes de mĂ©taux de transition, obtenus par voie hydrotalcite, montre que la nature du cation bivalent joue un rĂŽle important. Les oxydes mixtes Co-Cu ont montrĂ© une meilleure activitĂ© que les matĂ©riaux composĂ©s d'un seul de ces deux Ă©lĂ©ments. Cependant, l'ajout d'eau dans le flux rĂ©actionnel conduit Ă une baisse d'activitĂ© des catalyseurs contenant du Cu
Insight into the praseodymium effect on the NH3-SCR reaction pathways over W or Nb supported ceria-zirconia based catalysts
International audienceThe partial substitution of zirconium for praseodymium in a ceria-zirconia support was studied for WO3 or Nb2O5 supported catalysts dedicated to the NOx SCR by NH3. This partial substitution favored the support reducibility, but both niobium and tungsten impregnation strongly inhibited the redox behaviors of the support. Concomitantly, Nb2O5 and WO3 also provided acidic sites but praseodymium noticeably inhibited the ammonia storage, especially for WO3-containing sample. Finally, praseodymium drastically decreased the deNOx performances. Additional NO and NH3 oxidation experiments were performed and the various redox and acidic behaviors of all the studied materials were suitable to provide an overview of the reactional pathways which begins by the oxidative dehydrogenation of NH3 on acid sites. The generated species react either with oxygen species or with gaseous NO, reflecting a strong competition between the NOx SCR and NH3 oxidation together with the formation of a key intermediate in the nitrogen oxides reduction
CoCuAl mixed oxides derived from hydrotalcite-like compounds for CO2 purification in oxyfuel combustion conditions
International audienc
NO reduction by CO under oxidative conditions over CoCuAl mixed oxides derived from hydrotalcite-like compounds: Effect of water
International audienceOxyfuel combustion is a promising technology to produce CO2 rich effluents. Nevertheless, storage as well as valorization steps require to increase the purity of these CO2 rich effluents due to the presence of CO and NOx produced during combustion process. In view of development of transition metal-based catalyst for this application, cobalt and/or copper derived hydrotalcite materials were used as precursor of oxide catalyst for NO-CO abatement in a gas stream similar to those obtained when an oxyfuel combustion is performed. Hydrotalcite precursors and catalysts were characterized by several techniques. The best catalytic performances for the NO-CO abatement are obtained with cobalt-aluminum mixed oxide catalyst. The impact of water was also investigated and following trends were obtained: (i) a decrease in activity for NO oxidation while no modification was observed for CO oxidation; (ii) a shift towards higher temperature for NO reduction while maintaining the same yield; (iii) an improved stability of the catalyst with time on stream
CoCuAl mixed oxides derived from hydrotalcite-like compounds for CO2 purification in oxyfuel combustion conditions
International audienc
Effect of Precious Metals on NO Reduction by CO in Oxidative Conditions
International audienceCarbon dioxide has become an environmental challenge, where the emissions have reached higher level than can be handled. In this regard, conversion of CO2 to value-added chemicals and thus recycling of CO2 appear a viable option. Prior to valorization, CO2 must be purified. Among several opportunities, oxyfuel combustion is a process in rapid development. However, the gases resulting from this process contain some traces of impurities that can hinder the recovery of CO2 such as NO and CO. This work has, therefore, focused on the study of the NO-CO reaction in an oxidizing medium, using heterogeneous catalytic materials based on various supported noble metals. These materials were extensively characterized by a variety of methods including BrunauerâEmmettâTeller (BET) surface area measurements, hydrogen chemisorption, transmission electron microscopy (TEM) and H2 temperature programmed reduction (H2-TPR). The results obtained show that the catalytic behavior of M/Al2O3 catalysts in CO oxidation and NO reduction with CO in oxidative conditions depends mainly on the nature of the metal. The best result for both reactions is obtained with Pt/Al2O3 catalyst. The Pt nanoparticles in their metallic form (Pt°) as evidenced by TPR could explain the activity
Investigation of catalysts M/CeO2 (Mâ=âPt, Rh, or Pd) for purification of CO2 derived from oxycombustion in the absence or presence of water
International audienceOxyfuel combustion is a promising technology to produce a CO2-rich flue gas ready suitable for sequestration or valorization. But its storage as well as its further valorization requires to increase the CO2 purification as a small amount of CO and NOx are produced during combustion. Based on the technology developed for three-way converters, similar systems, i.e., M/CeO2 where M is Pt, Pd, or Rh, were studied for NO-CO abatement in a gas stream similar to those obtained when an oxyfuel combustion is performed. The results evidenced that the role of the metal nature influences the performances obtained on NO-CO abatement, platinum supported on ceria being the most efficient catalyst. We also measured the impact of the presence of water in the reaction stream on the catalytic activity of these materials. It appears that the presence of water has a beneficial effect on the different reactions due to a water gas shift reaction that increases the reduction of the NO and favors the formation of N2. The study pointed out that platinum supported on ceria remained the best catalyst, under these wet operating conditions close to industrial ones, for purification of oxyfuel combustion exhausts
Binary CoOxâSiO 2 Porous Nanostructures for Catalytic CO Oxidation
International audienceThrough the integration of sol-gel chemistry, lyotrope mesophases and emulsions, the first CoOx-SiO2(HIPE) series of cobalt nano-oxides were embedded within silica macromesocellular self-standing hosts. These binary CoOx-SiO2 porous nanostructures (MUB-100(x)) series present an average of 95% porosity. We found out that high cobalt concentration maintains the hexagonal-2D organization of the mesoscopic voids when applying the thermal treatment at 700°C. Their specific surface areas fall between 400-500 m 2 g-1 when assessed from Ar physi-sorption measurements. At the microscopic length scale, as revealed through magnetic investigations, the low cobalt content foams MUB-100(1) and MUB-100(2) are made of the amorphous -Co(OH)2 phase coexisting with the silica network, while increasing the cobalt concentration during the one pot syntheses (MUB-100(3) and MUB-(4) materials) favors the formation of the spinel Co3O4 and olivine Co2SiO4 crystalline nanoparticles embedded within silica. When it turns towards the CO oxidation catalytic performance, the MUB-100(4) is able to totally convert the CO flow before 200°C (starting at 125°C) while achieving 50% of conversion for a light-off temperature T50 of 145°C, revealing the good efficiency of the MUB-100(4) in CO oxidation with which up to 4 catalytic cycles have been performed without disrupting drastically the catalytic performances while reaching thermodynamic stability from the cycle 2 to the cycle 4