Nanoscale Metal Oxide Particles/Clusters as Chemical Reagents. Adsorption of Hydrogen Halides, Nitric Oxide, and Sulfur Trioxide on Magnesium Oxide Nanocrystals and Compared with Microcrystals

Adsorption of HCl, HBr, NO and SO 3 on nanoscale MgO (autoclave prepared = AP-MgO) and microscale MgO (conventionally prepared = CP-MgO) has been studied. The higher surface area of AP-MgO allows a higher capacity of these gases to be adsorbed/mol MgO. However, at pressures of 100 Torr or higher, the amounts adsorbed/nm 2 for HX and SO 3 are larger on the microcrystals. This is explained as due to the formation of ordered multilayers of adsorbate on the more perfect crystals of CP-MgO (adsorption on flatter, more extended planes). In the case of NO, the different surface chemistry of AP-MgO vs CP-MgO is again demonstrated. In this case, AP-MgO adsorbed more NO/nm 2, and NO 2, N 2, and N 2 O were formed on the surface. The high surface area and unusual surface reactivity of nanoscale MgO allows it to be considered as a new type of adsorbent as well as a near-stoichiometric chemical reagent.