pressure, according to De Boer’s hysteresis,: at first the
pore structure consisted of cylindrical pores open at both
ends until 10000 psi, where it is replaced with tapered
or wedged shaped pores with narrow necks, open at one
or both ends.37 Indeed, these pore structures are different
from the NC-Al2O3 samples (see earlier results) and
quite different from NC-MgO, where pore volumes and
pore openings are smaller, and bottleneck and cylindrical
pores were observed.39
(39) Richards, R.; Li, W.; Decker, S.; Davidson, C.; Koper, O.;
Zaikovski, V.; Volodin, A.; Rieker, T.; Klabunde, K. J. J. Am. Chem.
Soc. 2000, 122, 4921.
Figure 2. HRTEM of NC-Al2O3.
Table 3. Aluminum/Magnesium Oxide Preparation
1 1/1 20 1 559
2 1/1 70 1 762
3 1/1 120 1 743
4 1/1 70 10 815
5 1/1 70 20 796
6 1/2 70 10 775
7 2/1 70 10 834
Figure 3. Surface areas of NC-Al2O3, CM-Al2O3, NC-MgO,
CM-MgO, and NC-(1/1)Al2O3/MgO upon heat treatment.
Nanocrystals of Al2O3 and Al2O3/MgO Chem. Mater. E
X-ray Diffraction. Figure 4 compares the XRD pattern
for the Mg and Al samples. The Al2O3/MgO did not
sinter even upon heating to 700 °C.
Infrared Spectroscopy. IR spectra were taken after
heat treatment at 25, 100, 200, 300, 400, and 500 °C. A
gradual loss of water and solvent was observed from 25
to 500 °C. So when the sample is activated at 500 °C, it
can be inferred that there will be a small amount of
residual surface -OH present.
Thermogravimetric Analysis. Weight loss under nitrogen
flow was about 40% and was found to be the
same when conducted in air. There was a gradual
weight loss throughout the heating, due to the hydroxide
converting to oxide and the removal of the water. The
theoretical weight loss is 34%, so the observed 40%
indicated that some adsorbed water was also present.
Transmission Electron Microscopy. Figures 1a, 5a,
and 5b show TEM photographs, of CM-Al2O3, NCAl2O3/
MgO, and CM-MgO, respectively. The CM-MgO
sample consists of single crystals of varying fairly large
sizes. The NC-Al2O3/MgO sample however consists of
crystallites having an average crystallite size of about
5 nm or smaller, and of quite different morphology from
analogous NC-Al2O3 and NC-MgO samples.39
ElementalAnalysis.Elementalanalysis results of NC(1/1)Al2O3/MgO preheat-treated to 500 °C under dynamic
vacuum were Mg ) 13.3% (17% calculated), Al
) 30.9% (37.9% calculated), C ) 0.65% (0% calculated)
and H ) 1.2% (0% calculated). Obviously some adsorbed
H2O and CO2 affected these results (as indicated by IR).
The formula MgAl2O3.3(OH)1.4(CO2)0.088(H2O)0.35 fits the
data (oxygen by difference). It was apparent from TGA
that some weakly bound water was present.
Adsorption Studies. Reaction of Al2O3 and (1/1)
Al2O3/MgO with CCl4. The reaction of CCl4 with Al2O3
and Al2O3/MgO was carried out to understand the
destructive adsorption abilities of the metal oxides
toward a model chlorocarbon at elevated temperatures.
Thermodynamics predicts that the samples containing
MgO should be more reactive than the Al2O3 samples.40
However, it will be seen how surface area, crystallite
size, and morphology can play an active role.
These reactions were conducted via the pulse method,
and the products were identified by GC. The breakthrough
injection, saturation injection, and molar ratios
are reported in Table 4.
Sulfur Dioxide Adsorption on Alumina, and Aluminum/
Magnesium Oxide. Adsorption of SO2 was carried
out to learn if the adsorption properties are different
for nanocrystals, when compared to commercial microcrystals.
Using 19.2 Å2 as the area of an SO2 molecule,
it can be determined that 5.2 molecules of SO2/nm2
would form a monolayer. The experimental results
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