Formation and migration of carbon produced in the dissociation of CO on Rh/TiO2(110)-(1 x 2) model catalyst: A scanning tunneling microscopy study

Scanning tunneling microscopy (STM) completed by Anger-electron spectroscop y (AES) and thermal desorption spectroscopy (TDS) measurements was applied for investigating the formation and thermal-induced migration of carbon nan oclusters produced by the decomposition of CO on Rh/TiO2(110)-(1 x 2) plana r catalyst. The annealing of a clean TiO2(110)-(1 x 2) surface in a CO atmo sphere (few millibar pressure) at 500 K results in the reconstruction of th e (1 x 2) structure into the (I x 4) arrangement. The same treatment of an Rh/TiO2(110)-(1 x 2) catalyst containing well-separated Rh nanocrystallites of approximately 10 nm in diameter leads to the formation of 3D carbon nan oclusters of 1-2 nm size. A fraction of the carbon formed on Rh nanoparticl es diffuses (probably also in cluster form) onto the support already at 500 K (spillover). In the temperature range of 700-1100 K the carbon clusters agglomerate and collapse into larger nanoparticles. The accumulation of car bon on the existing Rh nanoparticles occurs at above 1100 K. Annealing at 1 300 K causes the recovering of the original morphology of the Rh/TiO2 (110) -(1 x 2) catalyst, suggesting a total gasification of the surface carbon. T hese processes are accompanied by the oxidation of surface carbon by the bu lk oxygen of titania resulting in the formation of CO in the temperature ra nge 800-1300 K.