Gérard Delahay
École Normale Supérieure
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Featured researches published by Gérard Delahay.
Applied Catalysis B-environmental | 2003
Ariel Guzmán-Vargas; Gérard Delahay; Bernard Coq
Abstract The decomposition of N2O, and the catalytic reduction by NH3 of N2O and N2O + NO, have been studied on Fe-BEA, -ZSM-5 and -FER catalysts. These catalysts were prepared by classical ion exchange and characterized by TPR after various activation treatments. Fe-FER is the most active material in the catalytic decomposition because “oxo-species” reducible at low temperature, appearing upon interaction of FeII-zeolite with N2O (α-oxygen), are formed in largest amounts with this material. The decomposition of N2O is promoted by addition of NH3, and even more with NH3 + NO in the case of Fe-FER and -BEA. It is proposed that the NO-promoted reduction of N2O originated from the fast surface reaction between α-oxygen O∗ and NO∗ to yield NO2∗, which in turn reacts immediately with NH3.
Catalysis Letters | 1999
M. Mauvezin; Gérard Delahay; F. Kißlich; Bernard Coq; S. Kieger
The influence of ammonia on the reduction of N2O in presence of oxygen over Fe‐zeolite has been studied. It is found that BEA zeolite is the most efficient host structure for iron ions to catalyse the reduction of N2O with NH3.
Applied Catalysis B-environmental | 1997
C. Torre-Abreu; M.F. Ribeiro; C. Henriques; Gérard Delahay
Copper MFI zeolites with different Si/Al ratios and different copper loadings, prepared by ion exchange, were characterised by XRD, H2-TPR and NO TPD. The results indicated the existence of diverse copper species in CuMFI catalysts, such as isolated CU2+, Cu+ ions and CuO species, whose concentrations depends on the catalyst Si/Al ratio and copper loading. In underexchanged catalysts (catalysts with low Si/Al ratio or copper loading) in the copper mainly present as isolated Cu2+ ions, while in overexchanged catalysts (catalysts with high Si/Al ratio or copper loading) CuO species, Cu2+ and Cu+ ions were detected. CuMFI with high Si/Al ratio or high copper loading are more easily reduced than CuMFI with low Si/Al ratio or low copper loading. An easier reducibility of the copper species has an effect on the operating temperature window of the catalysts by decreasing the temperature of the maximum NO conversion. CuMFI zeolites with a high concentration of isolated Cu2+ ions exhibit the highest NO adsorption capacity. The results make evident that the isolated Cu2+ ions are the most active species for NO SCR by propene.
Applied Catalysis B-environmental | 1995
Gérard Delahay; Bernard Coq; L. Broussous
Abstract The selective catalytic reduction (SCR) of NO by decane has been investigated on a series of copper exchanged beta zeolite (BEA), and the catalytic behaviour has been compared to Cu-MFI. The different solids were characterised by temperature programmed reduction by H2 and temperature programmed desorption of NO in order to determine the nature, reducibility and accessibility of copper species. Only CuO aggregates are formed on Cu/H-BEA whatever the Cu content. By contrast, isolated Cu2+ are the main species occurring on Cu/Na-BEA when Cu exchange level is lower than 120% and the accessibility to Cu sites is high (NO/Cu≥ 0.45). At higher content, CuO aggregates exists too, and the accessibility decreases to NO/Cu≈ 0.29. The activity in SCR of NO by decane of Cu/Na-BEA goes through a maximum for 113% Cu exchange. This sample is less active than Cu/MFI at high temperature, but much more active at low temperature. The intrinsic activity at 673 K per accessible Cu site remains very similar for the different Cu/Na-BEA samples. This is attributed to temperatures of the reduction step Cu2+ → Cu2+ very close whatever the copper content.
Catalysis Today | 1999
Gérard Delahay; Bernard Coq; Stéphane Kieger; Bernard Neveu
The selective catalytic reduction (SCR) of NOx (NO + NO2) by NH3 in O2 rich atmosphere has been studied on Cu-FAU catalysts with Cu nominal exchange degree from 25 to 195%. NO2 promotes the NO conversion at NO/NO2 = 1 and low Cu content. This is in agreement with next-nearest-neighbor (NNN) Cu ions as the most active sites and with NxOy adsorbed species formed between NO and NO2 as a key intermediate. Special attention was paid to the origin of N2O formation. CuO aggregates form 40–50% of N2O at ca. 550 K and become inactive for the SCR above 650 K. NNN Cu ions located within the sodalite cages are active for N2O formation above 600 K. This formation is greatly enhanced when NO2 is present in the feed, and originated from the interaction between NO (or NO2) and NH3. The introduction of selected co-cations, e.g. Ba, reduces very significantly this N2O formation.
Applied Catalysis B-environmental | 1997
C. Torre-Abreu; M.F. Ribeiro; C. Henriques; Gérard Delahay
Abstract NO TPD, H 2 -TPR and XRD have been used to characterise copper-exchanged mordenites with different Si/Al ratios, copper contents and cocations. The results showed that copper is mainly in the form of isolated Cu 2+ ions in CuMOR catalysts with copper exchange ≤20%, whereas at higher copper exchange CuO species are also present. These results were obtained with H and Na as cocation and were achieved by changing either the catalyst Si/Al ratio or the copper content. The data also indicate that the cocation mainly affects copper location and that copper is more easily reduced in sodium form catalysts than in protonic form. It was found that the isolated Cu 2+ ions are the most effective species for NO adsorption and the most active species for NO SCR.
Catalysis Reviews-science and Engineering | 2006
Dorothée Berthomieu; Gérard Delahay
An overview of the CuI/IIY material is performed on the basis of the results obtained during the last 5 years on their structure (nature of the Cu species, siting, coordination …), their use and reactivity, based on TPR, XRD and various ex situ and in situ spectroscopies such as XAS, IR and EPR. A brief summary of previous work is reported to position these recent advances in the context of three decades of studies devoted to the characterization of these materials. Quantum mechanics modeling of both the structure and reactivity of the material is also reported, providing complementary information. Insights related to the properties of the catalysts obtained recently using this molecular approach are presented to demonstrate that this material behaves as a supermolecule. In addition to its adsorption properties, the zeolite Y is one of the most popular zeolite used in catalysis. When it is exchanged with copper, in selective adsorption processes, it has been shown to be a promising adsorbent in the desulfurization of transportation fuels. In the area of environmental applications, a new catalyst based on CuY zeolite is now used for NOx removal from the tail gas of nitric acid plants. Some selected examples are given to illustrate some of the CuY zeolite properties such as adsorption, deNOx elimination and biomimetic behavior.
Chemical Communications | 2004
G. Carja; Gérard Delahay; C. Signorile; Bernard Coq
A Fe-Ce-ZSM-5 catalyst elaborated from a new synthesis route exhibits very high NO conversion (75-100%) in the selective catalytic reduction of NO by NH(3) in a wide temperature window (523-823 K), even in the presence of H(2)O and SO(2).
Catalysis Letters | 1997
C. Torre-Abreu; M.F. Ribeiro; C. Henriques; F.R. Ribeiro; Gérard Delahay
Deactivation of CuMFI catalysts under NO selective catalytic reduction (SCR) by propene in both the absence and the presence of water was investigated as a function of zeolite form, Si/Al ratio and copper content. It was verified that the CuMFI deactivation extent is higher on H-form zeolite compared to Na-form and decreases when the copper exchange level increases, which can be achieved either by increasing the zeolite Si/Al ratio or the copper content. Furthermore, the results indicated that the catalyst deactivation is mainly due to a change in copper species rather than in MFI structure.
ChemPhysChem | 2002
Gérard Delahay; Enrique Ayala Villagomez; Jean-Marie Ducéré; Dorothée Berthomieu; Annick Goursot; Bernard Coq
The selective catalytic reduction (SCR) of NO by NH3 in the presence of O2 on Cu-faujasite (Cu-FAU) has been studied. Substitution of some Cu2+ with H+ and Na+ cations, compensating for the negative charge of the zeolite framework, forms the various CuHNa-FAU studied. The amount of Cu was held constant and the proportion of H+ and Na+ varied in the sample. The substitution of Na+ for H+ increases sharply the SCR rate by lowering the temperature of reaction by about 150 K. It is proposed that the rate increase mainly comes from an unhindered migration of Cu from hidden to active sites and a modification of the redox properties of Cu species. The former was demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO. The change in redox properties was demonstrated by a faster oxidation of Cu+ to Cu2+ (rate-determining step). Quantum chemical calculations on model clusters of CuHNa-FAU indicate that the faster rate of oxidation can be explained by a higher lability of protons in the absence of Na, which can be then removed from the catalyst more easily to yield H2O during the oxidation process.