Rhodium highly dispersed on alumina becomes partly poisoned by strongly bound CO when used for toluene hydrogenation at 348 K in the presence of CO2. Operando FT-IR analysis enabled to observed CO(ads) build up over the sample, while no CO(gas) could be measured in the reactor effluent. Analyses carried out by complementary operando and in situ infrared spectroscopy studies unraveled the nature of the deactivating sites, i.e. low coordination number Rh sites located at the interface with the alumina support basic sites on which CO2 strongly adsorbs. Rh supported on silica with a lower dispersion remained free of adsorbed carbon monoxide even under higher CO2 pressures, stressing the relevance of infrared studies in catalyst rational design.