Adsorption-induced structural changes of Rh supported by TiO2(110)-(1x2): An STM study

Effects of different gases (CO, NO, H-2, CO2) on the morphological changes of Rh nanoparticles deposited on TiO2(110)-(1 x 2) surface were studied by scanning tunneling microscopy. The planar model catalyst surface was prepar ed by evaporation of Rh on TiO2 at room temperature followed by annealing i n UHV. By the variation of the Rh content and the annealing temperature Rh nanoparticles can be produced in the range of 1-10 nn. A very rapid disinte gration of the supported Rh nanoparticles of 1-2 nn to atomically dispersed Rh was observed at 300 K even after a few minutes exposure to a pressure o f 10(-1) mbar CO. For particle sizes of 3-4 nm the CO-induced process becam e slower, and for larger Rh clusters (8-10 nm) it did not occur at all even at higher CO pressure. Keeping the atomically dispersed Rh in CO above 500 K led to the reformation of the Rh clusters but of larger size. The CO-ind uced agglomeration was also observed for larger Rh particles (5-6 nm) above 500 K. The adsorption of NO on Rh nanoparticles also resulted in the disru ption of Rh-x crystallites at 300 K. It was not observed, however, in the p resence of H-2 and CO2, which was explained by the different nature of thei r interaction with Rh. (C) 1999 Academic Press.