Moessbauer spectroscopy and catalytic studies on iron-exchanged, silicon-substituted Y-zeolite

Journal Article · Wed Apr 01 04:00:00 EST 1987 · J. Catal.; (United States)

OSTI ID:5366236

Aparicio, L M; Dumesic, J A; Fang, S; Long, M A; Ulla, M A; Millman, W S; Hall, W K

Iron-exchanged zeolites with Si/Al ratios ranging from 2.49 to 8.88 were characterized by Moessbauer spectroscopy and studied for the decomposition of N/sub 2/O. Moessbauer spectra were collected at room temperature after pretreatments in H/sub 2/ and O/sub 2/ at 700 K, and after exposure of the samples to CO or H/sub 2/O. Nitrous oxide decomposition activities were determined at 800 K under a N/sub 2/O partial pressure of 3.5 kPa. Moessbauer spectra collected after pretreatment in H/sub 2/ showed that silicon-substituted Fe-Y had a larger fraction of iron cations in sites I', II', and/or II than conventional Fe-Y, in which most iron cations were in site I. The silicon-substituted Fe-Y catalysts had higher turnover frequencies for the decomposition of N/sub 2/O than conventional Fe-Y. Moessbauer spectra collected after pretreatment in O/sub 2/ showed that a fraction of the iron cations in silicon-substituted Fe-Y was more difficult to oxidize to Fe/sup 3 +/ than the iron in conventional Fe-Y. Moessbauer spectra collected after pretreatment in O/sub 2/ showed that a fraction of the iron cations in silicon-substituted Fe-Y was more difficult to oxidize to Fe/sup 3 +/ than the iron in conventional Fe-Y. This result suggests that pairs of iron cations in close proximity are needed for the oxidation process to occur readily. Finally, exposure of the zeolites to CO or H/sub 2/O produced Moessbauer spectroscopy doublets due to iron cations associated with adsorbate molecules. These doublets indicate that ferrous cations at sites I', II', and/or II serve as adsorption centers for H/sub 2/O, the adsorption process increasing the coordination of the ferrous cations, and that ferrous cations at site II can serve as adsorption centers for CO as well. 22 references.

• Research Organization: Univ. of Wisconsin, Madison
• OSTI ID: 5366236
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 104:2; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ADSORPTION
ALUMINIUM
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
DECOMPOSITION
ELEMENTS
HYDROGEN
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IRON
MATERIALS
METALS
MINERALS
MOESSBAUER EFFECT
NITROGEN COMPOUNDS
NITROGEN OXIDES
NITROUS OXIDE
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
QUANTITY RATIO
SEMIMETALS
SILICON
SORPTION
SPECTROSCOPY
STEAM
SURFACE PROPERTIES
SYNTHESIS
TRANSITION ELEMENTS
YTTRIUM
ZEOLITES