Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen Full article
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Multifunctionality of Catalytically Active Centers and Their Detection : 2nd symposium 01-01 Jun 2002 , Schwäbisches Bildungszentrum, Kloster Irsee |
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| Journal |
Topics in Catalysis
ISSN: 1022-5528 , E-ISSN: 1572-9028 |
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| Output data | Year: 2003, Volume: 23, Number: 1-4, Pages: 137-143 Pages count : 7 DOI: 10.1023/A:1024832606400 | ||
| Tags | FeZSM-5; Fe complexes; activation; alpha-sites; alpha-oxygen; N2O decomposition | ||
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Abstract:
According to previous Mössbauer data [1] α-sites formation at the activation of Fe-containing zeolites is accompanied by irreversible “self-reduction” of the iron, proceeding without participation of an external reducing agent. Reduced Fe2+ ions are inert to O2 but are reversibly oxidized to Fe3+ by N2O, generating the α-oxygen species, Oα, which provide selective oxidation of hydrocarbons.
In this work, the mechanism of α-sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of “self-reduction”. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-β), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O2, which is accompanied by the immediate formation of α-sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of α-sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O2- ion, removed at the activation, is equivalent to two α-oxygen atoms. So, α-oxygen is identified as an ion-radical species Oα-., whose unique oxidation properties still distinguish it from the generally observed O-. radicals.
The mechanism of α-sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe2+ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O2.
Cite:
Starokon E.V.
, Dubkov K.A.
, Pirutko L.V.
, Panov G.I.
Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen
Topics in Catalysis. 2003. V.23. N1-4. P.137-143. DOI: 10.1023/A:1024832606400 WOS РИНЦ ANCAN OpenAlex
Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen
Topics in Catalysis. 2003. V.23. N1-4. P.137-143. DOI: 10.1023/A:1024832606400 WOS РИНЦ ANCAN OpenAlex
Dates:
| Published print: | Aug 1, 2003 |
Identifiers:
| Web of science: | WOS:000184336800014 |
| Elibrary: | 21096286 |
| Chemical Abstracts: | 2003:560576 |
| Chemical Abstracts (print): | 139:281712 |
| OpenAlex: | W207231410 |