Abstract In a previous work, a silver alumina catalyst was synthesized according to a novel route involving mechanical mixture of silver oxides and alumina and a further hydrothermal treatment. As nano-sized silver particles direct characterization is rather difficult either by electron microscopy, XPS or XRD, an alternative method consists in studying their interaction with adsorbed molecule. Upon adsorption followed by infrared spectroscopy, CO is indeed an efficient probe molecule enabling to characterize the state of metal particles, thanks to its highly sensitive ν(CO) vibration. In the present work, CO was thus adsorbed at room temperature after reducing or oxidizing pre-treatments. Not only information on the metal state was obtained but it was also evidenced that CO dissociates at 298K onto pre-reduced silver leading to both carbon deposit and carbonate formation.