The low temp. gas phase oxidn. of ammonia to nitrogen has been studied over alumina-supported, silica-supported and unsupported silver catalysts. TPD, TPR, TEM, XRD and FT-Raman were used to characterize the different silver catalysts. The results showed alumina-supported silver to be the best catalyst due to the interaction of silver with alumina. Pre-treatment had a great affect on the catalyst performance. Redn. in hydrogen at 200 DegC without any pre-calcination gave the best activity. At least four types of oxygen species were obsd. when silver was present in oxygen at high temp. These species are adsorbed mol. oxygen, adsorbed at. oxygen, subsurface oxygen and bulk dissolved oxygen, resp. Ammonia oxidn. activity at low temp. is related to the catalysts ability to dissociative or non-dissociative adsorption of oxygen. In addn., a good correlation existed between the N2 selectivity for selective catalytic oxidn. (SCO) reaction and the selective catalytic redn. (SCR) activity of NO with NH3 for the silver-based catalysts, i.e. the higher SCR yield of nitrogen, the higher the SCO selectivity N2.