An FTIR study of surface ceria hydroxy groups during a redox process with H2

Abstract

Two ceria samples with differing specific surface areas and porosities have been investigated by IR spectroscopy. A ν(OH) band at ca. 3510 cm^–1 was found to be due to cerium oxyhydroxide impurities within the ceria pores. One-, two- and three-coordinated OH species were observed. Doubly bridging OH species in the vicinity of surface oxygen vacancies were found to be very reactive towards D₂ dissociation at 423 K, when the reduction is surface limited. At 673 K, doubly bridging OH species and hydrogen-bonded ones were formed when the already reduced ceria surface was exposed to H₂. These OH species were not stable upon evacuation and are proposed to be responsible for the so-called reversible H₂-reduction of ceria.