Preparation and characterization of iron-exchanged zeolites in environmental pollution application for de-NOx

Dans ce travail, la réaction d'oxydation du NO-en-NO2 a été étudiée, dans le but de consolider certaines hypothèses mécanistiques établies pour la SCR des NOx par NH3. Une première étape de ce travail a consisté à préparer des échantillons de zéolithe de type fer. La caractérisation d échantillons frais et vieillis de façon hydrothermale a ensuite été conduite au moyen de la spectroscopie IR. L activité des catalyseurs a enfin été étudiée pour la réaction d oxydation de NO en NO2 signalée comme l'étape déterminante dans l'élimination des NOx par NH3. Des zéolithes échangées au fer ont donc été utilisées comme catalyseurs actifs et leur vieillissement a été étudié en utilisant un certain nombre de techniques de caractérisation de surface, comme la diffraction des rayons X, MET, BET, Mössbauer, FTIR et la spectroscopie I.R operando. Le premier objectif principal de cette thèse a été de déterminer la technique de préparation la plus pertinente de catalyseurs Fe-FER et de leurs mécanismes de dégradation sous différentes conditions de vieillissement. Le deuxième objectif de cette recherche est de trouver, via la méthodologie operando, le meilleur mécanisme pour l oxydation de NO-en-NO2 décrite comme l étape déterminante de l élimination des NOx par NH3. Les résultats de cette thèse peuvent être utilisés dans le développement de meilleurs catalyseurs appliqués en réduction des NOx par NH3. Ces derniers posséderont une bonne résistance aux changements physiques et chimiques, et préserveront une capacité d'oxydation de NO-en-NO2 intéressante et donc une bonne efficacité dé-NOx.The aim of this work was first to characterize exchanged Fe2+ cations in fresh and aged FeFER catalysts by IR spectroscopy and then to study NO-to-NO2 oxidation ability which is the determing step in NOx removal by SCR with NH3. Fe exchanged zeolite-based were used as active catalysts and their aging-induced changes were studied by surface characterization techniques, such as X-ray diffraction, TEM, BET, Mössbauer, FTIR and operando spectroscopy. The aging was applied in a series of FeFER catalysts for which the effects of increasing temperatures under wet atmosphere were considered. The main goal of this thesis is to determine the preparation technique of Fe-FER catalysts together with their degradation mechanisms under different aging conditions. The catalyst s properties, thus, the applicability of multiple techniques will provide a larger view of the aging phenomenon of FeFER catalysts. The second goal of this research is to find, by mean of the operando methodology, the best mechanism for NO-to-NO2 oxidation which is described as the rate determing step of SCR with NH3. The catalytic properties of iron-containing ferrierite under reaction conditions were thus investigated in this contribution. The results of this thesis can be used in the development of better catalysts used in SCR with NH3 that are resistant in particular to physical and chemical changes while preserving interesting NO-to-NO2 oxidation capacity and thus NOx SCR efficiency.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

A kinetic study of the NO to NO2 oxidation mechanism over Fe FER: a combined analysis of operando surface and gas phase data

International audienc

A kinetic study of the NO to NO2 oxidation mechanism over Fe FER: a combined analysis of operando surface and gas phase data

International audienc

Adsorption properties of Fe-containing dealuminated BEA zeolites as revealed by FTIR spectroscopy

Times Cited: 1 Article English Cited References Count: 83 582viAdsorption properties of Fe-containing dealuminated BEA zeolites were investigated by FTIR spectroscopy of adsorbed CO and NO. Two Fe-containing SiBEA zeolite samples were prepared by a two-step post-synthesis method: creation of vacant T-atom sites (T = Si, Al) by dealumination of tetraethylammonium BEA zeolite with nitric acid followed by impregnation of the resulting SiBEA zeolite with an aqueous solution of Fe(NO3)(3). The two samples differed in iron content (0.9 and 4.2 wt.%, for Fe(0.9)SiBEA and Fe-4.2-SiBEA, respectively). The parent SiBEA sample was characterized by IR bands at 3735 cm(-1) (isolated internal silanols), 3705 and 3515 cm-1 (associated with hydroxyl nests at vacant T-atom sites). Upon the impregnation step, the bands at 3705 and 3515 cm(-1) practically disappeared, indicating consumption of the corresponding hydroxyls and incorporation of iron into the framework of SiBEA zeolite (also confirmed by XRD). In agreement with this, the IR spectra of the two samples revealed acidic bridging hydroxyls of a Fe3+-O(H)-Si type characterized by a band at 3632 cm(-1) in higher concentration for Fe(4.2)SiBEA. The 3632 cm(-1) band shifted to 3352 cm(-1) after low-temperature CO adsorption (Delta nu similar to 280 cm(-1)) evidencing a high acidity of the bridging OH groups. Low-temperature CO adsorption experiments revealed the presence of mainly two families of Fen+ sites, evidenced by carbonyl bands at 2215 and 2186 cm(-1), respectively. The latter sites were in higher concentration for Fe(4.2)SiBEA. In addition, a minor fraction of iron sites were found to be able to form tricarbonyls (bands at 2155, 2123 and 2115 cm(-1)). It was also deduced that the majority of iron introduced was in a Fe3+ state and the majority of these ions did not interact with probe molecules. Adsorption of NO leads to appearance of different mononitrosyls (1901, 1869 and 1842 cm(-1)). With time and in the presence of NO, polynitrosyls (1920 and 1815 cm(-1)) were also formed. Experiments on coadsorption of CO and NO reveal that the iron sites producing the 2215 cm(-1) carbonyls form nitrosyl species absorbing at 1901 cm(-1). It is suggested that highly electrophilic Fe3+ ions act as adsorption sites in this case. Treatment of the samples with CO at 673 K generated new Fe2+ sites monitored by CO at 2183, 2174 and 2166 cm(-1). NO adsorption revealed different mono-, di- and polynitrosyl species. A peculiarity in this case was that interconversion between poly- and dinitrosyl species was well observed. The amount of reduced iron was much higher for Fe(4.2)SiBEA than for Fe(0.9)SiBEA. (C) 2009 Elsevier Inc. All rights reserved

Evidencing three distinct Fe-II sites in Fe-FER zeolites by using CO and NO as complementary IR probes

International audienceFe-FER zeolites were characterized by FTIR spectroscopy of adsorbed CO and NO. Two aged samples (Fe-FER-1 and Fe-FER-4 with Fe content of 1.1 and 3.7 wt%, respectively) and one freshly prepared Fe-57 rich sample (Fe-57-FER, designed for Mossbauer studies and containing 1.5 wt% Fe) were studied. Both CO and NO are adsorbed onto Fe2+ cations and have different sensitivities to their location and/or coordination state. CO adsorption on Fe-FER-1 reveals two kinds of Fe2+ sites with the respective complexes observed at 2195 and 2189 cm(-1). The principal carbonyls (2195 cm(-1)) are easily converted into dicarbonyls (2188 cm(-1)) at low temperature and high CO equilibrium pressure. NO is less sensitive than CO to the environment of Fe2+ ions and NO adsorption gives rise to a single band at 1878 cm(-1). However, careful analysis reveals that this band consists of two closely located components. With the Fe-FER-4 sample a third family of iron sites was detected by CO at 2196 cm(-1). These carbonyl species are stepwise converted to di- (similar to 2188 cm(-1)) and tricarbonyls (similar to 2180 cm(-1)). With these sites NO forms another nitrosyls clearly detected at 1895 cm(-1). The latter are converted with time into polynitrosyls. These new sites are very sensitive to the preliminary treatment and easily change their oxidation state, forming Fe2+/Fe3+ redox couples. The sample preliminary treated with oxygen at 673 K is characterized by Fe3+-OH groups (3674 cm(-1)) and reactive oxygen that produces carbonates when reacting with CO, and NO+ when interacting with NO. Adsorption of NO on a freshly prepared Fe-57-FER sample confirms the presence of the three distinct Fe2+ sites which is consistent with Mossbauer data. Finally, summarizing all the data, location of the different sites inside the FER structure is proposed. The results obtained are discussed in relation with the catalytic performance of Fe-FER. (C) 2009 Elsevier B.V. All rights reserved

Evidencing three distinct Fe-II sites in Fe-FER zeolites by using CO and NO as complementary IR probes

International audienceFe-FER zeolites were characterized by FTIR spectroscopy of adsorbed CO and NO. Two aged samples (Fe-FER-1 and Fe-FER-4 with Fe content of 1.1 and 3.7 wt%, respectively) and one freshly prepared Fe-57 rich sample (Fe-57-FER, designed for Mossbauer studies and containing 1.5 wt% Fe) were studied. Both CO and NO are adsorbed onto Fe2+ cations and have different sensitivities to their location and/or coordination state. CO adsorption on Fe-FER-1 reveals two kinds of Fe2+ sites with the respective complexes observed at 2195 and 2189 cm(-1). The principal carbonyls (2195 cm(-1)) are easily converted into dicarbonyls (2188 cm(-1)) at low temperature and high CO equilibrium pressure. NO is less sensitive than CO to the environment of Fe2+ ions and NO adsorption gives rise to a single band at 1878 cm(-1). However, careful analysis reveals that this band consists of two closely located components. With the Fe-FER-4 sample a third family of iron sites was detected by CO at 2196 cm(-1). These carbonyl species are stepwise converted to di- (similar to 2188 cm(-1)) and tricarbonyls (similar to 2180 cm(-1)). With these sites NO forms another nitrosyls clearly detected at 1895 cm(-1). The latter are converted with time into polynitrosyls. These new sites are very sensitive to the preliminary treatment and easily change their oxidation state, forming Fe2+/Fe3+ redox couples. The sample preliminary treated with oxygen at 673 K is characterized by Fe3+-OH groups (3674 cm(-1)) and reactive oxygen that produces carbonates when reacting with CO, and NO+ when interacting with NO. Adsorption of NO on a freshly prepared Fe-57-FER sample confirms the presence of the three distinct Fe2+ sites which is consistent with Mossbauer data. Finally, summarizing all the data, location of the different sites inside the FER structure is proposed. The results obtained are discussed in relation with the catalytic performance of Fe-FER. (C) 2009 Elsevier B.V. All rights reserved

Iron Nitrosyl Species in Fe-FER: A Complementary Mossbauer and FTIR Spectroscopy Study

International audienceFTIR spectroscopy was applied to the investigation of the nitrosyl complexes formed with the extra-framework iron species in Fe-ferrierite (Fe-FER). To clarify the loading effect oil the nature Of file species formed. six ferrierites with Fe loadings varying between 0 and 3.7 wt % were prepared via ionic exchange and investigated. A Fe/SiO(2) and a Fe-FER sample containing iron oxide were also Studied for comparison purposes. Adsorption of NO on Fe-FER (containing no iron oxide species) gives different nitrosyl species. and different iron sites call be evidenced depending on the iron concentration. The bands are assigned to mononitrosyl oil iron whose oxidation state is determined to be +2 thanks to Mossbauer spectroscopy. In particular, one specific Fe(2+)-cation (typical of a highly loaded sample) appears to be easily converted to Fe(3+) upon oxygen treatment, which makes these sites excellent candidates for catalytically active redox sites

Iron Nitrosyl Species in Fe-FER: A Complementary Mossbauer and FTIR Spectroscopy Study

International audienceFTIR spectroscopy was applied to the investigation of the nitrosyl complexes formed with the extra-framework iron species in Fe-ferrierite (Fe-FER). To clarify the loading effect oil the nature Of file species formed. six ferrierites with Fe loadings varying between 0 and 3.7 wt % were prepared via ionic exchange and investigated. A Fe/SiO(2) and a Fe-FER sample containing iron oxide were also Studied for comparison purposes. Adsorption of NO on Fe-FER (containing no iron oxide species) gives different nitrosyl species. and different iron sites call be evidenced depending on the iron concentration. The bands are assigned to mononitrosyl oil iron whose oxidation state is determined to be +2 thanks to Mossbauer spectroscopy. In particular, one specific Fe(2+)-cation (typical of a highly loaded sample) appears to be easily converted to Fe(3+) upon oxygen treatment, which makes these sites excellent candidates for catalytically active redox sites

Iron Nitrosyl Species in Fe-FER: A Complementary Mossbauer and FTIR Spectroscopy Study

International audienceFTIR spectroscopy was applied to the investigation of the nitrosyl complexes formed with the extra-framework iron species in Fe-ferrierite (Fe-FER). To clarify the loading effect oil the nature Of file species formed. six ferrierites with Fe loadings varying between 0 and 3.7 wt % were prepared via ionic exchange and investigated. A Fe/SiO(2) and a Fe-FER sample containing iron oxide were also Studied for comparison purposes. Adsorption of NO on Fe-FER (containing no iron oxide species) gives different nitrosyl species. and different iron sites call be evidenced depending on the iron concentration. The bands are assigned to mononitrosyl oil iron whose oxidation state is determined to be +2 thanks to Mossbauer spectroscopy. In particular, one specific Fe(2+)-cation (typical of a highly loaded sample) appears to be easily converted to Fe(3+) upon oxygen treatment, which makes these sites excellent candidates for catalytically active redox sites