The oxidation states and dispersion of silver supported on alumina and faujasite were monitored by TEM, TPR and in situ UV-visible spectroscopy along the steps of thermal dehydration, then oxidation and finally reduction of the freshly prepared materials. An original transmission electron microscopy approach was conducted, based on the use of a pseudo-environmental TEM holder that provides direct observations, on given zones of the samples, of the formation (in the case of zeolite) or not (in the case of alumina) of reduced silver particles upon dehydration of the material in air. Besides, the question of the high propensity of the silver species supported on alumina to be reduced in hydrogen at temperatures as low as ambient temperature is addressed.