Adsorbate induced phase changes of rhodium on TiO 2(110)

Abstract

The adsorption of [Rh(CO) 2Cl] 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 v sym ( C O) and v asym( C O) observed at 2112 and 2028 cm −1, respectively. The gem-dicarbonyl decomposes through loss of CO at 450–500 K to produce metallic rhodium particles, Rh 0 x . 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 0 x , with v( C O) observed at 2064 cm −1. Desorption of the linear bound species from Rh 0 x takes place at 550–600 K. 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 0 x gives rise to the linear CO species with v( C O) at 2064-2055 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 v( C O) of the bridge bound species.