in molar ratios of 1:1 or other desired ratios. The point is to obtain intimately intermingled mixtures, essentially molecular in nature, and gain advantages by obtaining higher surface areas of the more reactive component throughout the structure, in this case MgO (more basic in nature) with Al2O3 (which supports very
high surface areas). Thus, the so obtained Al2O3 and Al2O3/MgO materials
reported herein are higher in surface area than materials reported before, and remarkably thermally stable (with minimal sintering even as high as 700 °C) and
are essentially amorphous or at least have crystal domains 2 nm or less. Most importantly, the chemical adsorptive properties of these materials are remarkable.
There are three features of nanocrystalline materials that affect their chemical reactivities: (1) high surface areas, meaning large surface-to-bulk ratios; (2) unusual
morphologies; (3) crystal disorder.39,51-53 All three of these features are present in materials at hand, as their high chemical reactivity has demonstrated. In fact, these
ultrafine powders behave as stoichiometric reagents in some reactions, such as CCl4 destructive adsorption. In surface adsorption processes, such as with SO2 and
Paraoxon, very large capacities are realized due to both surface area and enhanced surface reactivity. Note the amounts adsorbed normalized for surface areas (Tables
5 and 6). An additional interesting feature for the mixed sample Al2O3/MgO is that the reactivity of this material is superior to NC-Al2O3. This is probably due to the
greater Lewis basicity of the MgO present, which should be and is beneficial for adsorption of the acid gas SO2 (see Table 5). This effect is also evident in the Paraoxon adsorption results (Table 6) where considerably higher. These results indicate that the NC-Al2O3/MgO mixed product has enhanced chemical reactivity properties over NC-Al2O3 or NC-MgO. This is an advantageous result and must be due to the Lewis base nature of MgO being preserved while maintaining the large pore volume and large surface area of the Al2O3 partner. This suggests that intimate commingling of many other nanocrystalline oxides could provide enhanced reactivities, in a sense tailored to the desired properties.
The support of the National Science Foundation and the Army Research Office are
acknowledged with gratitude. CM011590I (47) Lin-Vien, D.; Colthup, N.; Fateley, W.; Grasselli, J. The
Handbook of Infrared and Raman Characteristic Frequencies of
Organic Molecules; Academic Press: New York, 1991.
(48) Pretsch, E.; Clerc, T.; Seibl, J.; Simon, W. Tables of Spectral
Data for Structure Determination of Organic Compounds; SpringerVerlag: New York, 1989.
(49) Diao, Y.; Walawender, W.; Sorenson, C. M.; Klabunde, K. J.
Chem. Mater. 2002, 14, 362.
(50) (a) Kistner, S. S. J. Phys. Chem. 1932, 36, 52. (b) Teichner, S.
J.; Nicolaon, G. A.; Vicarini, M. A.; Gardes, G. E. E. Adv. Colloid
Interface Sci. 1976, 5, 245.
(51) Decker, S.; Lagadic, I.; Klabunde, K. J.; Michalowicz, A.;
Moscovici, J. Chem. Mater. 1998, 10, 674.
(52) Itoh, Utamapanya, S.; Stark, J. V.; Klabunde, K. J.; Schlup,
J. Chem. Mater. 1993, 5, 71.
(53) Jiang, Y.; Decker, S.; Mohs, C.; Klabunde, K. J. J. Catal. 1998,
Table 7. FTIR Bands for Free and Adsorbed Paraoxon
free Paraoxon assignment adsorbed Paraoxon assignment
860 Ó(C-N) 860 Ó(C-N)
930 CH3 rock 930 CH3 rock
1045 Ó(Et-O-(P)) 1045 Ó(C-O-(P))
1107 CH3 rock 1107 CH3 rock
1164 CH3 rock 1164 CH3 rock
1296 Ó(PdO) 1313 Ó(PdO)
1348 Ós(N-O) 1348 Ós(N-O)
1491 Ó(C-C ring) 1491 Ó(C-C ring)
1526 Óas N-O 1526
1593 Ó(C-C ring) 1593 Ó(C-C ring)
H Chem. Mater. PAGE EST: 8 Carnes et al.
Чтобы распечатать файл, скачайте его (в формате Word).
Ссылка на скачивание - внизу страницы.