Surface-enhanced Raman spectroscopy was used to study two silver-based catalysts following exposure to C 2H 4 O 2 mixtures at different temperatures. The catalysts were formed in one of two ways. In the first, aqueous silver colloid was filtered through a silica glass fiber filter. In the second, silver metal was electrochemically deposited in the pores of anodic aluminum oxide. Spectral features due to amorphous carbon were detected at 1370 and 1596 cm −1. Samples heated in ethylene-rich mixtures displayed the carbon peaks up to a temperature of 455 K beyond which the carbon features were essentially absent. A spectral feature was observed at 995 cm −1. This and another weaker spectral feature at 676 cm −1, which was seen only in the spectrum of the sample below 400 K, showed a frequency shift upon using 18O 2 and were therefore assigned to vibrations involving oxygen. Tentatively they were ascribed to O 2 − and O 2 −2 moieties.