Active Sites in Fe/MFI Catalysts for NOx Reduction and Oscillating N2O Decomposition

El-Malki, El-M; Santen, van Ra Rutger; Sachtler, W. M. H.

doi:10.1006/jcat.2000.3034

Cited by 206 publications

(144 citation statements)

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“…2). Water [10,11]. Surface migration of iron may lead to the binuclear Fe-center I (see Scheme 1), and its presence in FeZSM-5 has been proven experimentally [12].…”

Section: Effect Of the Catalyst Pre-treatment On The Formation Of Actmentioning

confidence: 95%

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

2004

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The surface active Fe-sites in HZSM-5 with low content of iron (<1000 ppm) activated by steaming and high temperature (up to 1323 K) calcination in inert lead to the formation of surface oxygen (O) ad species from N 2 O and were characterized quantitatively by transient response method. Only a part of (O) ad deposited on zeolite by decomposing N 2 O was active in CO oxidation at 523 K. A binuclear Fe-center is suggested as an active center, featuring a "diamond core" structure, similar to that of the monooxygenase enzyme. The active O-atoms were assigned to the paired terminal oxygen atoms each bound to one Fe-site in the binuclear [Fe 2 O 2 H] + -cluster.Zeolite pre-saturated by water vapor at 473-523 K generates (O) ad species from N 2 O completely inactive in the CO oxidation. The total amount of the oxygen, (O) ad , deposited on the pre-saturated by water zeolite corresponds to a half of stoichiometric amount of the surface Fe-atoms and suggests that water blocks a half of the binuclear [Fe 2 O 2 H] + -center, the remaining acting as a single Fe-site.

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“…2). Water [10,11]. Surface migration of iron may lead to the binuclear Fe-center I (see Scheme 1), and its presence in FeZSM-5 has been proven experimentally [12].…”

Section: Effect Of the Catalyst Pre-treatment On The Formation Of Actmentioning

confidence: 95%

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

2004

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“…The synthesis solution was prepared from sodium aluminate (52.5 wt% NaAlO 2 , Riedel-de Haën), sodium chloride (99.5 wt%, Fluka), and tetrapropylammonium hydroxide (20 wt% in water, Fluka) in deionized water by adding the tetraethyl orthosilicate (TEOS, 98%, Merck-Suchardt) with vigorous stirring (2-3 h). The molar ratio was as follows: TPA-OH:Si(OEt) 4 :NaCl:NaAlO 2 :H 2 O = 2.16:5.62:3.43:0.13: 1000. The synthesis took 2 days under an autogenously regulated pressure at 444 K. After being washed and calcined at 873 K in air for 5 h, the zeolite was converted into H form using ammonia buffer, and heated in nitrogen at 823 K for 5 h. For activation the zeolites were steamed (H 2 O partial pressure was 310 mbar) in a N 2 flow for 3 h at 823 K and treated in He for 4 h at 1323 K. This treatment did not alter zeolite structure as was shown by X-ray diffraction (XRD) of the zeolites before and after activation.…”

Section: Synthesis Of Catalystsmentioning

confidence: 99%

“…The kinetics of N 2 O decomposition was shown to be of first order in N 2 O concentration [4]. The activity of zeolites in N 2 O decomposition is known to depend on the presence of NO x , O 2 , H 2 O, SO 2 , CO, and hydrocarbons in streams.…”

Section: Introductionmentioning

confidence: 98%

“…HZSM-5 with a low content of iron (hereafter H(Fe)ZSM-5) was shown to be active in nitrous oxide decomposition, forming surface atomic oxygen (O) ad and gaseous N 2 and O 2 [3]. The sites in H(Fe)ZSM-5 active in the above-mentioned processes have been assigned to iron cations [3][4][5][6]. But until now very little quantitative information has been available on the total loading of (O) ad and its role during N 2 O decomposition to O 2 and N 2 .…”

Section: Introductionmentioning

confidence: 99%

“…The activity of zeolites in N 2 O decomposition is known to depend on the presence of NO x , O 2 , H 2 O, SO 2 , CO, and hydrocarbons in streams. El-Malki et al [4,10] and Zhu et al [5] did not find any effect of oxygen on this reaction, but in the presence of water vapor, isothermal oscillations were observed during N 2 O decomposition with Fe/MFI [4,10]. Perez-Ramirez et al [6,11] studied the effect of NO on N 2 O decomposition and showed that oxygen desorption is the rate-limiting step, which could be accelerated by NO.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of N2O decomposition over HZSM-5 with low Fe content

Bulushev

Kiwi‐Minsker

Renken

2004

Journal of Catalysis

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The dynamics of N 2 O decomposition to gaseous nitrogen and oxygen over HZSM-5 catalysts with a low iron content (200 and 1000 ppm) was studied by the transient response method in the temperature range 523-653 K. The active catalysts were prepared from HZSM-5 with Fe in the framework on its steaming at 823 K followed by thermal activation in He at 1323 K. Two main steps were distinguished in the dynamics of N 2 O decomposition. The first step represents N 2 O decomposition forming gaseous nitrogen and surface atomic oxygen. The second step is associated with surface oxygen recombination and desorption. At 523-553 K only the first step is observed. Above 573 K the decomposition of N 2 O to O 2 and N 2 in stoichiometric amounts starts at a rate increasing with time until a steady-state value is reached. This increase was assigned to the catalysis by adsorbed NO formed slowly on the catalyst surface from N 2 O, as indicated by temperature-programmed desorption. The catalytic effect of the adsorbed NO was also confirmed by transient experiments with forced addition of NO in the stream of N 2 O during its decomposition. A simplified kinetic model is proposed to explain the autocatalytic reaction. Catalyst pretreatment in O 2 did not affect N 2 O decomposition, but irreversible water vapor adsorption at 603 K resulted in a twofold decrease in surface oxygen loading from N 2 O and complete inhibition of the oxygen desorption.

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Application of Microporous Materials as Ion‐Exchangers

Schmidt

2002

Handbook of Porous Solids

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Active Sites in Fe/MFI Catalysts for NOx Reduction and Oscillating N2O Decomposition

Cited by 206 publications

References 40 publications

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

Dynamics of N2O decomposition over HZSM-5 with low Fe content

Application of Microporous Materials as Ion‐Exchangers

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