|
N. I. Morozova, I. I. Kulakova, M. I. Afanasov, P. B. Fabritchnyi
Impact of surface-located tin,
antimony or tellurium cations on the
dehydration of isopropanol in the presence
of Cr2O3 catalyst investigated by means of
mossbauer spectroscopy
Abstract
Catalytic properties of
various samples containing 119Sn, 121Sb or 125Te cations immediately on the surface of Cr2O3 crystallites
are compared in the reaction of dehydration of isopropanol. For all the
samples, including the undoped reference one, dependences of the logarithm of
specific rate of reaction lnW vs 1/T exhibit, upon increasing the
temperature, an inflexion point at 610 K. On subsequent lowering the
temperature the dependence of lnW
remains unchanged for the reference sample and the tellurium-doped one whereas
it becomes linear in the whole studied temperature range for both tin-doped and
antimony-doped samples. In situ
Mossbauer measurements show Sn4+ and Sb5+ ions to be
reduced upon the dehydration process to Sn2+ and Sb3+
while tellurium preserves its +4 valence state. No one of surface-located Sn2+,
Sb3+ and Te4+ isoelectronic cations significantly affects the
activation energy of reaction. This can be accounted for by the location of
these cations on low co-ordination surface sites prohibiting them from bonding
to OH groups that are presumed to be part of active centers.
Copyright (C) Chemistry Dept., Moscow State University, 2002
|
|
