Res. Chem. Intermed.
, Vol. 33, No. 8–9, pp. 689–703 (2007)
Also available online - www.brill.nl/rci
EPR and Raman investigations into anionic redox
chemistry of nanoporous 12CaO·7Al
, STEFAN WITKOWSKI
and ZBIGNIEW SOJKA
Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Cracow, Poland
Regional Laboratory of Physicochemical Analyses and Structural Research,
Ingardena 3, 30-060 Cracow, Poland
Received 12 May 2006; accepted 24 June 2006
Abstract—EPR and Raman spectroscopy jointed with temperature-programmed reduction (TPR) and
oxidation (TPO) were used to elucidate of the anionic redox processes occurring during the interaction
of dioxygen, nitrous oxide and dihydrogen with nanoporous 12CaO·7Al
. The results showed that
hydrogen and oxygen enter the mayenite cages following a dissociative pathway involving hydride,
hydroxyl and peroxide intermediates, respectively. Generation and annihilation of the cage O
radicals upon oxidative and reductive treatments, conﬁned to the near to the surface region, were
found to be reversible. The key intermediates of this process were identiﬁed and a detailed mechanism
of the surface and cage reactions was proposed.
Keywords: Mayenite; 12CaO·7Al
; EPR spectroscopy; Raman spectroscopy; TPO; TPR; N
dioxygen; dihydrogen; redox; C12A7.
Owing to their unique features, markedly different from the parent bulk solids,
nano-scaled oxides are nowadays focusing a growing interest resulting from the
new possibilities of producing advanced materials and catalysts [1, 2]. Beneﬁcially
different morphology, nanoporosity and unique surface structure greatly enhance
their physical properties and chemical activity. In addition, nano-crystalline
materials may dissolve higher concentration of foreign ions expanding the scope
for tailoring new catalytic and advanced functional ceramic materials .
The way in which the electronic charge is distributed between cations and
anions determines the prototypic chemical functioning of oxides, epitomized within
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