IR spectroscopy of low temperature adsorbed CO and CO+NO has been used to characterize the surface species on a 5% Ni-YSZ catalyst. Dispersed surface Ni species are present on the fresh catalyst, essentially formed by Ni2+, although it is evident that these species are very easily reduced in very mild conditions to zerovalent atomic nickel. Reduction in stronger conditions gives rise to small Ni metal particles, which are however easily reoxidized to bivalent nickel. This work has demonstrated how elastic is the redox state of this catalyst. This is supposed to be a key properties explaining the behaviour of this catalyst in converting ethanol in the presence of water.