Synthesis, Characterization, and Adsorption Studies of Nanocrystalline Aluminum Oxide and a Bimetallic, страница 3

into KBr pellets and studied.

Thermogravimetric Analysis (TGA). TGA was used to determine

the conversion of Al(OH)2 to Al2O3 during heat

treatment. These studies were conducted under a nitrogen

flow. To measure the weight loss the Al2O3 samples were

placed in a basket and heated at a rate of 10°/min from room

temperature to 700 °C. The instrument used was a thermogravimetric

analyzer TGA-50 from the Shimadzu Co.

Elemental Analysis. Al2O3 after heat treatment was transferred

to glass vials, under argon atmosphere, and sent to

Galbraith Laboratories for analysis. Elemental analysis was

conducted for Al, C, and H. The amount of oxygen was obtained

by subtracting the sum of Al, C, and H from 100.

Adsorption Studies. Reaction of Al2O3 and Al2O3/MgO

with CCl4. These reactions were conducted in a U-tube that

was connected to a gas chromatograph (GOW-MAC gas chromatograph

series 580).34 The U-tube was made of Pyrex and

connected between the injector port and the column (Alltech

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B Chem. Mater. Carnes et al.

Chromosorb W-HP). An oxide sample (0.100 g) was placed in

the U-tube between two small plugs of quartz wool. The most

favorable temperatures for both reactions were found to be at

500 °C, and the U-tube was heated to this temperature. The

injector port was kept at 100 °C. Injections of 2 ÌL of CCl4

were made every 7 min. Any CO2 coming off the sample, or

CCl4 that was not destroyed, was then sent via helium (20

cm3/min) through the column (90 °C) to be separated. They

were then detected by a thermal conductivity detector (120

°C) and peak areas recorded. Injections of CCl4 were made

until the oxide bed had been exhausted.

Sulfur Dioxide Adsorption. A quartz spring balance was

used to measure the adsorption of SO2 onto Al2O3 and Al2O3/

MgO. The apparatus consists of a basket, which is used to hold

the sample, and this is attached to a quartz spring.35 The

basket and the spring are closed within the vacuum line. The

SO2 gas tank is also attached to the vacuum line. As the SO2

adsorbs onto the metal oxide in the basket, the weight change

causes the spring to move, and this movement is noted by a

telescope. Once the telescope is calibrated, it is accurate to

(0.1 mg.

Granules (100 mg) of oxides were placed into the basket on

the spring balance. The samples were placed under dynamic

vacuum for 1 h at room temperature. After evacuation, the

vacuum line was closed to the pump and the spring position

was noted. The SO2 gas was allowed to fill the vacuum line,

including the spring balance to the desired pressure. The

spring position was noted over the next hour. This was followed

by 100 min of evacuation to remove all physisorbed species.

After the evacuation the spring position was noted again, indicating