Redox behaviour of over-exchanged Fe/ZSM5 zeolites studied with in-situ soft X-ray absorption spectroscopy

被引:29
作者
Heijboer, WM
Battiston, AA
Knop-Gericke, A
Hävecker, M
Bluhm, H
Weckhuysen, BM
Koningsberger, DC
de Groot, FMF
机构
[1] Univ Utrecht, Debije Inst, Dept Inorgan Chem & Catalysis, NL-3584 CA Utrecht, Netherlands
[2] Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany
关键词
D O I
10.1039/b306130m
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The oxidation and reduction behaviour of calcined over-exchanged Fe/ZSM5 has been studied using soft X-ray absorption by measuring the average iron valence under (2 mbar) helium, oxygen and deNOx (HC-SCR) conditions between room temperature and 350 degreesC. The results ( probing depth of approximately 4 nm) show that Fe/ZSM5 is an extremely flexible redox system. The calcination procedure (severe calcination: heating rate 5 degreesC min(-1), as normally used in the literature; mild calcination: heating rate 0.5 degreesC min(-1)) is proven to be important to optimise the reducibility of iron. Upon mild calcination Fe/ZSM5 has an average valence of 2.9 under oxygen (5% in helium), of 2.5 under pure helium at room temperature (RT), and of 2.1 under pure helium at 350 degreesC. Upon severe calcination Fe/ZSM5 shows higher average valences, in agreement with the assumption that part of the iron in this sample is positioned in small iron-oxide nanoparticles at the outer surface of the zeolite crystals. During heating in helium, the valence reaches a minimum value before slightly rising again (re-oxidation) when the temperature is kept constant. It is also found that the X-ray irradiation is able to affect the average valence by values up to 0.10. This study confirms that iron in 'over-exchanged' Fe/ ZSM5 consists dominantly of highly reactive iron complexes, where the iron is ( distorted) octahedral Fe-III in the oxidised state. The implications for the reaction mechanism for the N2O decomposition and the nature of the alpha-oxygen sites are discussed, in relation to recent developments in the understanding of iron non-heme enzymes.
引用
收藏
页码:4484 / 4491
页数:8
相关论文
共 37 条
[1]   PROBING DEPTH OF SOFT-X-RAY ABSORPTION-SPECTROSCOPY MEASURED IN TOTAL-ELECTRON-YIELD MODE [J].
ABBATE, M ;
GOEDKOOP, JB ;
DEGROOT, FMF ;
GRIONI, M ;
FUGGLE, JC ;
HOFMANN, S ;
PETERSEN, H ;
SACCHI, M .
SURFACE AND INTERFACE ANALYSIS, 1992, 18 (01) :65-69
[2]   Reactivity of binuclear Fe complexes in over-exchanged Fe/ZSM5, studied by in situ XAFS spectroscopy - 2. Selective catalytic reduction of NO with isobutane [J].
Battiston, AA ;
Bitter, JH ;
Koningsberger, DC .
JOURNAL OF CATALYSIS, 2003, 218 (01) :163-177
[3]   Reactivity of Fe-binuclear complexes in over-exchanged Fe/ZSM5, studied by in situ XAFS spectroscopy -: Part 1:: Heat treatment in He and O2 [J].
Battiston, AA ;
Bitter, JH ;
Heijboer, WM ;
de Groot, FMF ;
Koningsberger, DC .
JOURNAL OF CATALYSIS, 2003, 215 (02) :279-293
[4]   Evolution of Fe species during the synthesis of over-exchanged Fe/ZSM5 obtained by chemical vapor deposition of FeCl3 [J].
Battiston, AA ;
Bitter, JH ;
de Groot, FMF ;
Overweg, AR ;
Stephan, O ;
van Bokhoven, JA ;
Kooyman, PJ ;
van der Spek, C ;
Vankó, G ;
Koningsberger, DC .
JOURNAL OF CATALYSIS, 2003, 213 (02) :251-271
[5]   Evolution of extraframework iron species in Fe silicalite 1. Effect of Fe content, activation temperature, and interaction with redox agents [J].
Berlier, G ;
Spoto, G ;
Bordiga, S ;
Ricchiardi, G ;
Fisicaro, P ;
Zecchina, A ;
Rossetti, I ;
Selli, E ;
Forni, L ;
Giamello, E ;
Lamberti, C .
JOURNAL OF CATALYSIS, 2002, 208 (01) :64-82
[6]   Activity and durability of Fe/ZSM-5 catalysts for lean burn NOx reduction in the presence of water vapor [J].
Chen, HY ;
Sachtler, WMH .
CATALYSIS TODAY, 1998, 42 (1-2) :73-83
[7]   High resolution X-ray emission and X-ray absorption spectroscopy [J].
de Groot, F .
CHEMICAL REVIEWS, 2001, 101 (06) :1779-1808
[8]   X-RAY-ABSORPTION AND DICHROISM OF TRANSITION-METALS AND THEIR COMPOUNDS [J].
DEGROOT, FMF .
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 1994, 67 (04) :529-622
[9]  
DEGROOT FMF, 2003, IN SITU SPECTROSCOPY
[10]   High-pressure soft X-ray absorption spectroscopy:: application of a new in situ spectroscopic method in catalysis research [J].
Hävecker, M ;
Knop-Gericke, A ;
Schedel-Niedrig, T .
APPLIED SURFACE SCIENCE, 1999, 142 (1-4) :438-442