The effect of TiOx on the bonding of CO test molecules to different Rh surfaces has been investigated in model systems under UHV conditions. The TiOx overlayers had a twofold effect both on Rh nanoparticles and Ar+-ion sputtered Rh films prepared on TiO2(1 1 0). They suppressed the uptake of molecular CO by a site blocking mechanism. In the other mechanism the recombinative CO desorption states went through a maximum at intermediate TiOx coverages on both kinds of rhodium surfaces, indicating the promotion of CO decomposition. These findings are in harmony with earlier high pressure studies which showed that the methanation rate of CO on rhodium is maximal at intermediate TiOx coverages. The effect of a TiOx film underneath a Rh deposit (0.4 monolayer) on its surface chemistry has also been addressed. A Rh-TiOx-Rh structure was formed at 230 K by the deposition of Rh on a continuous TiOx film supported by a 20 monolayer thick Rh multilayer. CO desorption curves indicated a highly reactive Rh overlayer at 230 K and also a dramatic structural change in the rather narrow temperature range of 230-265 K. The rearrangement is accompanied by the migration of TiOx species onto the post-deposited Rh as it can be deduced from the appearance of a CO desorption feature with T-p =360 K. The driving force of the process is the formation of strong Rh-Rh bonds and the low surface free energy of TiOx overlayer with respect to the bare Rh surface. (C) 2014 Elsevier B.V. All rights reserved.