Adsorbate induced phase changes of rhodium on TiO2(110)

Abstract

The adsorption of [Rh(CO) 2 Cl] 2 on TiO 2 (110) has been studied using FT-RAIRS ans XPS, and at 300 K results in dissociation to produce adsorbed chlorine and the rhodium gem-dicarbonyl species Rh(CO) 2 . The gem-dicarbonyl is characterised in the IR by ν sym (CO) and v asym (CO) observed at 2112 and 2028 cm −1 , respectively. The gem-dicarbonyl d decomposes through loss of CO at 450–500 K to produce metallic rhodium particles, Rh x 0 . Following heating to 500 K, re-exposure of the surface to ∼10 6 L of CO gives rise to the partial re-generation of the gem-dicarbonyl species, and in addition to the adsorption of linearly bound CO on Rh x 0 , with ν (CO) observed at 2064 cm −1 . Desorption of the linear bound species from Rh x 0 takes place at 550–600 K. The re-generation of the gem-dicarbonyl species also takes place on a surface where adsorbed chlorine has been removed using water adsorption/desorption cycles, but does not appear to involve surface hydroxyl groups or dissociative adsorption of CO. If the surface is heated to 800 K it appears that larger metal clusters are formed which do not allow the regeneration of the gem-dicarbonyl following exposure to ∼10 6 L of CO. Adsorption of CO on these larger particles of Rh x 0 gives rise to the linear CO species with ν (CO) at 2055–2064 cm −1 , and shoulders at 2030 and 2010 cm −1 . In addition a broad band at 1870 cm −1 is observed which is associated with ν (CO) of the bridge bound species.