AN FTIR STUDY OF SURFACE CERIA HYDROXY-GROUPS DURING A REDOX PROCESS WITH H-2

Two ceria samples with differing specific surface areas and porosities have been investigated by IR spectroscopy. A nu(OH) band at ca. 3510 cm(-1) was found to be due to cerium oxyhydroxide impurities within th e ceria pores. One-, two- and three-coordinated OH species were observ ed. Doubly bridging OH species in the vicinity of surface oxygen vacan cies were found to be very reactive towards D-2 dissociation at 423 K, when the reduction is surface limited. At 673 K, doubly bridging OH s pecies and hydrogen-bonded ones were formed when the already reduced c eria surface was exposed to H-2. These OH species were not stable upon evacuation and are proposed to be responsible for the so-called rever sible H-2-reduction of ceria.