MIXED-VALENCE OXIDE DISPERSION-INDUCED MICROPORE FILLING OF SUPERCRITICAL NO

Ultrafine Ti(IV)-doped alpha-FeOOH particles were dispersed on the high-surface-area carbon fibers of uniform micropores in order to elucidate the role of the surface electronic factor in the micropore filling of supercritical NO. EXAFS and XANES showed that dispersed Ti-doped alpha-FeOOH particles are ultrafine and have the same local structure as that of bulk alpha-FeOOH particles. The microporosity of the samples did not change significantly by the doping of Ti(IV) in dispersed alpha-FeOOH on the basis of N2 adsorption. Also, the surface acidic site concentration measured by the irreversible NH3 adsorption was almost constant regardless of the Ti doping. However, doping of Ti(IV) in the dispersed alpha-FeOOH enhanced the micropore filling of supercritical NO by 40%, at the maximum. The enhancement of the NO micropore filling by Ti doping was presumed to come from the increase of quasi-free electrons in the dispersed alpha-FeOOH fine particles due to mixed valence formation, which is enhanced by the surface segregation of Ti(IV) from the XPS examinations.