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 SO3 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 SO3 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 NO2, N-2, and N2O 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.