Powders of nanocrystalline metal oxides were compared with common macrocrystalline powders and minerals for their ability to reflect near-infrared light (NIR) (750−2500 nm). The nanocrystalline metal oxides were found to possess higher NIR reflectance values (∼15−20%) and this can be attributed to their smaller crystallite sizes coupled with smaller mean aggregate sizes in accordance with the Kubelka−Munk theory.

Magnesium oxide nanocrystals are shown to be selective catalysts for the benzylation of aromatics with benzyl chloride, in the order xylene > toluene >> benzene. Normal polycrystalline MgO is not as effective as the nanomaterials. However, at the highest surface area, normally most reactive MgO samples (aerogel prepared AP-MgO) were poorer catalysts than a hexagonal platelet form (CP-MgO) of lower surface area. During the catalysis, the MgO is partially converted to MgCl(2), but crystal shape differences are not washed out. Rate data, differential thermal analysis, and consideration of crystal shapes and faces suggest that the CP-MgO form is most catalytically active because of optimal adsorption, molecular trafficking, and desorption energies. The AP-MgO apparently adsorbs the reactants too strongly, and thereby this hinders the catalytic process. These results serve as another example of where nanocrystalline shape plays an important role.

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