Synthesis, Characterization, and Adsorption Studies of Nanocrystalline Aluminum Oxide and a Bimetallic, страница 2

the autoclave reached 265 °C, the reactor was vented to the

atmosphere, very quickly removing the solvent vapors (which

took about 1 min). Next the furnace was removed and the

bomb was flushed with nitrogen for 10 min to remove the

remaining solvent vapors. The autoclave was allowed to cool

to room temperature, yielding a fluffy, white Al(OH)3, which

was placed in a Schlenk tube, connected to a vacuum line, and

surrounded by a furnace. The Schlenk tube was evacuated at

room temperature for 1 h. Next it was slowly heated from room

temperature to 500 °C while under dynamic vacuum. After

the heat treatment was complete, the furnace was turned off

and the Schlenk tube was allowed to cool to room temperature,

while still under dynamic vacuum. After heat treatment, the

aluminum oxide had a light gray color, due to a small amount

of carbon formation (from pyrolysis of residual alkoxy groups).

Synthesis of High Surface Area Mixed NC-Al2O3/MgO.

First the magnesium methoxide solution, was prepared, which is briefly described here. Under argon 0.500 g (0.020mol) of Mg that had been sandpapered, wiped clean with an acetone-wet Kimwipe, and cut into small pieces, was added to a 200 mL round-bottom flask. To the Mg was added 50 mL of methanol, and this was allowed to react while stirring overnight to form a clear colorless solution. Fifty milliliters of

toluene was added to this solution, and it was allowed to stir for 2 h. In a separate 500 mL round-bottom flask, under argon, 1.00 g (0.0040 mol) of aluminum tri-tert-butoxide was added. This was dissolved in a solution of 100 mL of toluene, and 40

mL of tert-butyl alcohol to form a clear colorless solution. The alkoxide solutions were mixed to give the desired molar percentages and then hydrolyzed, with a solution containing a stoichiometric amount of distilled water in 70 mL of absolute

ethanol (added dropwise). The reaction was then stirred at room temperature for 10 h. During this time the reaction mixture remains a clear colorless liquidlike gel. The hydroxide sol-gel was transferred to a glass liner of a Parr autoclave, and dried as described for the pure alumina system. Thermal conversion of aluminum hydroxide/magnesium hydroxide to aluminum oxide/magnesium oxide was carried out as described for the pure alumina system. After heat treatment, the aluminum/magnesium oxide had a light gray color.

Characterization. Transmission Electron Microscopy

(TEM). TEM studies were carried out by adding dry ethanol

to the heat-treated Al2O3, and sonicating this slurry for 5 min

using a Branson 1210 sonicator. A drop of this slurry was then

placed onto a carbon-coated copper grid. TEM experiments

were performed using a Philips 201 TEM or a Philips CM12


Brunauer-Emmet-Teller (BET). Surface area measurements

were done by using BET methods. These were conducted

using both Micromeritics Flowsorb II 2300 and Quantachrome

NOVA 1200 instrumentation. The samples were first

outgassed at the desired temperature and then allowed to cool

to room temperature.

Powder X-ray Diffraction (XRD). For XRD studies the Al2O3

samples were heat treated under vacuum directly before being

placed onto the sample holder. The instrument used was a

Scintag XDS 2000 spectrometer. Cu KR radiation was the light

source used with applied voltage of 40 kV and current of 40

mA. The 2ý angles ranged from 20 to 85° with a speed of 2°/

min. The crystallite size was then calculated from the XRD

spectra using the Scherrer equation.

Infrared Spectroscopy (FT-IR). FT-IR was used to observe

solvent removal during the heat treatment process. These

experiments were conducted on an RS-1 FTIR spectrometer

from Mattson with a liquid-nitrogen-cooled MCT detector.

Heat-treated samples of NC-Al2O3 and CM-Al2O3 were made