Catalytic solid state reactions on the surface of nanoscale metal oxide particles

Core-shell nanoparticles of metal oxides ([Fe2O3]MgO, [Fe2O3]CaO, [V2O3]MgO, and the other first-row transition metal shell materials coated on nanoparticles of MgO or CaO) have been studied as destructive adsorbents for CCl4, CHCl=CCl2, C5H4Cl2, CN3P(O)(OCH3)(2), and SO2. A catalytic effect due to the transition metal shell material has been observed, where solid state ion-ion exchange takes place, thus allowing penetration into the MgO or CaO particles and thereby regenerating the transition metal oxide for additional catalytic action. Due to this catalytic effect, the destructive adsorption reaction became nearly stoichiometric, and therefore much higher capacities for destruction/immobilization of the adsorbate under study were realized; For example, the reaction CCl4 + [V2O5]MgO --> CO2 + [V2O5]MgCl2 is greatly enhanced by the presence of the V2O5, and VCl5 or VCl3 appear to be intermediates in the process. The catalytic effects are proposed to be due to the intermediacy of transition metal chlorides, phosphates, or sulfites, which are mobile and seek out reactive sites on the MgO or CaO nanoparticles where ion-ion exchange can most readily take place, thereby regenerating the transition metaloxide catalyst. (C) 1998 Academic Press.