Synthesis, Characterization, and Adsorption Studies of Nanocrystalline Aluminum Oxide and a Bimetallic, страница 9

we can estimate that about 0.77 monolayer is adsorbed

under these conditions. In a 0.0350 g sample of NCAl2O3/

MgO 2.8 _ 1019 nm2 surface is available, and so

we can estimate that about 1.04 monolayers are adsorbed

under these conditions (room temperature, 0.01

M concentration in pentane).

After the reaction was complete, the powders were

filtered, and IR studies were done on the solids. The

results from the IR show that the NC samples have

many new species adsorbed to the powder, whereas the

CM samples have little if any new species adsorbed.

Table 7 gives IR spectra assignments for free Paraoxon

and for adsorbed Paraoxon which are based on the

literature.33,41,42,47,48 According to IR spectra taken following

the reaction with Paraoxon for CM-Al2O3, NC(41) Koper, O. Properties of High Surface Area Calcium Oxide and

its Reactivity Towards Chlorocarbons. Ph.D. Thesis, Kansas State

University, 1996.

(42) Stark, J. V.; Klabunde, K. J. Chem. Mater. 1996, 8, 1913-1918.

(43) Goodsel, A. J.; Low, M. J. D.; Takezawa, N. Environ. Sci.

Technol. 1972, 6, 3, 268.

(44) Dunn, J. P.; Koppula, P. R.; Stenger, H. G.; Wachs, I. E. Appl.

Catal., B 1998, 19, 103.

(45) Stark, J. Characterization and Studies of Reactivity of Magnesium

Oxide. M.S. Thesis, Kansas State University, 1995.

(46) Li, Y.; Schlup, J.; Klabunde, K. J. Langmuir 1991, 7, 1388.

Figure 5. Transmission electron microscope pictures: (a)

NC-Al2O3/MgO; (b) CM-MgO.

Figure 6. IR spectra after 2 h evacuation at room temperature.

Table 6. Destructive Adsorption of Paraoxon in Pentane

on the Oxide Powders

sample molar ratio

NC-Al2O3 1 mol of Paraoxon:11 mol of Al2O3

CM-Al2O3 1 mol of Paraoxon:63 mol of Al2O3

NC-(1/1) Al2O3/MgO 1 mol of Paraoxon:5.6 mol of Al2O3/MgO

CM-MgO 1 mol of Paraoxon:188 mol of MgO

NC-MgO 1 mol of Paraoxon:46 mol of MgO

Nanocrystals of Al2O3 and Al2O3/MgO Chem. Mater. G

Al2O3, CM-MgO, and NC-(1/1)Al2O3/MgO, there was

some change when Paraoxon was adsorbed. A band at

1296 cm-1 assigned to Ó(PdO) was broadened and

shifted to approximately 1313 cm-1. Also, the original

peak for free Paraoxon at 1232 cm-1 assigned to the

Ó(P-O-Ar) stretch had disappeared. The band due to

Ó(P-O-Et) at 1045 cm-1 did not change much (see

Table 7), suggesting that the EtO-P moieties were not

perturbed or destroyed. We tentatively conclude from

these data that PdO bond is strongly perturbed through

binding to Lewis acid sites on the Al2O3 and MgO

surfaces and that the P-OAr bond is broken.


The modified aerogel procedure employed is designed to yield high quality gels under apid gelation conditions. 49 Solvent-to-alkoxide ratios are important as well as the solvent choice. The addition of toluene has at least two effects; lowering viscosity and polarity. This in turn, causes a more rapid hydrolysis step and faster gelation, which results in a more “open” structure.49 After supercritical drying50 very high surface area Al(OH)3 or mixed MgAl(OH)4 were obtained. Subsequently, after dehydration of the hydroxides, high surface area oxides with large pore volumes were obtained. This synthetic approach is very different from earlier reports, where reactive sputtering,12 dc arc plasmas,13 crysol techniques,14 and related sol-gel methods were

used.16,17 For example Ramesh and co-workers17 used aluminum triisopropoxide as a starting material in a sol-gel synthesis and obtained amorphous Al2O3, surface

area 97-183 m2/g, much lower than the Al2O3 samples reported herein. Earlier work on mixed Al2O3/MgO systems dealt with impregnating Al2O3 with magnesium salts followed by heat treating; surface areas of 136-184 m2/g were reported. In addition, Chi and Chang report that Al2O3 impregnated with MgO could adsorb more NO at 523 K than did a series of other similar compositions. It should be emphasized that the modified aerogel procedure reported herein is intended to prepare MgOAl2O3