Surface Chemistry of Nanocrystalline Oxides of Magnesium and Aluminum
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In recent years the study of the nanocrystalline MgO and Al2O3 has increased because of the potential importance of these methods as catalysts and adsorbents. This research has ranged from preparation of these ultrafine powders with surface areas on the order of 500 to 600 m2/g for MgO and 600 to 700 m2/g for Al2O3 to the chemistry occurring on the surface of these unique particles. Most of the work on nanocrystalline MgO and Al2O3 has centered on the adsorption and reactions of gases or easily vaporized liquids at elevated temperatures or under high vacuum with very little focusing on the reactions at room temperature with neat liquids or solutions. Very little has been reported on the surface reactions of these particles in slurries with the organic substrate dissolved in the solvent. The purpose of this paper is to introduce recent developments of solvent effects on the surface chemistry of nanoparticle MgO and Al2O3 with organic substrates.
The adsorption and reactions of some organic substrates on aerogel prepared (AP)-MgO and nanocrystalline (NC)-Al2O3 have been reported as vapor reactions, reactions of the neat liquid substrate, and reactions in solvents ranging from pentane to methanol. These reactions yielded elimination and substitution products. Reactions in pentane showed a greater degree of reactivity on both the AP-MgO and NC-Al2O3 surfaces than reactions involving neat organic substrates. More polar solvents, such as tetrahydrofuran (THF) and methanol, gave results quite different than the hydrocarbon solvent. These studies have also shown that reactivity of AP-MgO and NC-Al2O3 is greater than the reactivity of the bulk materials and is due to more than the surface areas of these nanocrystalline materials.