Yang Bo

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Yang Bo 2012.6.26
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Introduction
The writer report the first study of the
hydrolysis of tetraethyl ortho-silicate (TEOS) in
an aqueous solution of N, N, N-trimethyl-1-adamant
ammonium (TMAda) hydroxide, the clear sol
precursor for the preparation of the high-silica
zeolite SSZ-13 (CHA). The initial stages of the
hydrolysis of TEOS were monitored by
quantitative Si and Al nuclear magnetic resonance
(NMR) and small-angle X-ray scattering (SAXS). Si
NMR allowed quantitative characterization of Si
in nanoparticles and dissolved oligomers and
measuring the average Si - O-Si connectivity. The
writer try to elucidate the effect of the
organocation TMAda and the presence of Al on
chemical composition, internal connectivity, and
stability of precursor nanoparticles as well as
soluble species.
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Result and Discussion

This has also been observed with the silicalite-1
and silicalite-2 systems when TPAOH and TBAOH are
used as SDA, and thus, this seems to be a general
pattern for alkylammonium-based silicate sols
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Si-distribution
Figure 2. (a) Si-distribution in TEOS (),
oligomers ( ?), and nanoparticles ( ?) during the
hydrolysis of TEOS in TMAdaOH. (b) Comparison of
the Si distribution for CHA,MEL, and MFI systems.
TEOS decreases as a straight line similar to that
in panel a.
At this stage , the organic SDA acts as the
hydroxide ion source adjusting the pH of the
medium , and affecting the stability of the
silicate species present in solut ion by shifting
the hydrolysis , condensation , and precipitation
equilibria .
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Si-distribution
In identifying the different Si species, we have
employed the following chemical shift ranges Q0
-71 to -72 ppm, Q1andQ2? - 79 to - 83 ppm, Q2and
Q3? -86 to -91 ppm, Q3- 92 to - 100 ppm, and
Q4 -100 to -108 ppm.
Figure 3. Si-distribution in (a) all oligomers
and (c) nanoparticles during the hydrolysis
of TEOS in TMAdaOH.
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SAXS patterns
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Hydrolysis of TEOS in the Aluminosilicate System
77 to 73,72 to 67, 66 to 62, and 61 to 54 ppm,
assigned, respectively, to q0/q1and q2,q3, and q4
Figure 7. Evolution of (a)27Al NMR spectra of
clear sols/solutionswith the progress of TEOS
hydrolysis. (b) Evolution of chemical shifts of
qn Al sites with Si/TMAdaOH ratio.
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The role of the aluminum is to connect oligomers
within the nanoparticles into core shell
elements. As aluminum exhibits a lower activation
energy than Si for metal oxygen bond breaking
reformation, it catalyzes the core shell
networking within the nanoparticles.
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27Al NMR

The 27Al spectra are only affected by the change
in Si/TMAdaOH ratio and the connectivity of Si.
This means that aluminate species behave like
silicate species.
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Transformation of LEV-type zeolite into less
dense CHA-type zeolite Ikuhiro Goto, Masaya
Itakura, Syohei Shibata, Koutaro Honda, Yusuke
Ide, Masahiro Sadakane, Tsuneji Sano
Microporous and Mesoporous Materials 158 (2012)
117122
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Introduction
In general, medium/large pore size and
high-silica zeolites are synthesized by
hydrothermal treatment of amorphous
aluminosilicate hydrogel as a starting material
in the presence of organic structure-directing
agents (OSDAs). The use of OSDAs is, however,
undesirable from a practical point of view,
because of their high cost as well as their large
environmental impact. Hydrothermal conversion
of LEV-type zeolite into CHA-type zeolite
occurred in the absence of both anorganic
structure-directing agent and a seed crystal.
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SEM Images
Fig. 2. SEM images of (a) starting LEV, (b) CHA
(Sample No. 1), (c) CHA (Sample No. 8),
Fig. 2 (b) and (c) show SEM images of the
obtained CHA-type zeolites. The crystal
morphology was cubic, and the crystals were
200400 nm in size, which is smaller than the
crystal size of the starting LEV-type zeolite, as
shown in Fig. 2(a)
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Influence of the Synthesis Temperature
. When the hydrothermal conversion of LEV-type
zeolite was carried out at 125170?for 1.5 h, the
LEV-type zeolite was transformed into CHA-type
zeolite. At 200?, pure ANA-type zeolite was
ob-tained, suggesting that CHA-type zeolite
transformed into the most stable zeolite. At 90
?, pure CHA zeolite was obtained when
the synthesis time was prolonged to 12 h. The
morphology and crystal size of the CHA-type
zeolite crystals obtained at 90 ?were similarto
those obtained at 125 ?.
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Influence of the Si/Al Ratio
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LEVCHA and LEVLTA
LEV- and CHA-type zeolites have similar composite
building units because these two zeolites both
belong to chabazite group, whereas there was less
similarity between the composite units of LEV-
and LTA-type zeolites.
It was suggested that locally ordered
aluminosilicate species (nanoparts) produced by
decomposition/dissolution of the starting
LEV-type zeolite contribute to the transformation
process.
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Thanks for your attention