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Abstract:
Using
an
optimized
procedure, large
SAPO-5
single
crystals
(up
to
250
X
75 µm)
with
a
very
high
optical
quality
could
be
synthesized.
NMR
spectroscopy
proved
the
perfect incorporation
of
silicon
on
phosphorus sites.
IR
microscopy
with polarized
IR
radiation
revealed
that
both
types
of
OH
groups,
with absorption
bands
at
3627
and
3519
cm-1,
are
oriented
almost
perpendicularly
to
the
crystal
c-axis,
thus
protruding
into
the
12-membered
and
the
6-membered
ring
channels,
respectively. Adsorbed p-xylene
reacts with both types
of
OH
groups,
giving
rise
to
one broad band
for
the
OH
vibration
at
3233
cm-1,
which
indicates
a
shift
of
the
proton from
the
6-membered ring
to
the
12-membered
ring.
From
the
dichroic ratios
of
the
bands
due
to
the
p-xylene,
it can
be inferred
that the
long axis
of
the
p-xylene
molecule is
oriented parallel
to
the
channel
axis
of
the
molecular
sieve.
