Oxygen chemisorption on an electrolytic silver catalyst: a combined TPD and Raman spectroscopic study

In situ Raman spectroscopy, temperature programmed desorption (TPD) and scanning electron microscopy (SEM) were used to study the interaction of an electrolytic silver catalyst with O2 at atmospheric pressure and temperatures between 300 and 923 K. Raman spectroscopy and TPD were applied to characterise the chemisorbed oxygen species formed during catalyst exposure to O2 under these conditions. SEM was used to examine changes in catalyst morphology caused by high temperature oxygen treatment. The silver catalyst chemisorbed oxygen in a variety of distinct states over the temperature range examined. Oxygen species, identified on the basis of their vibrational and thermal desorption spectra, were a molecular superoxo species, weakly chemisorbed surface atomic oxygen (Oα), strongly chemisorbed surface atomic oxygen (Oγ) and subsurface oxygen (Oβ). The thermal stability and formation conditions of each species were established through a combination of in situ Raman and TPD data. With heating in O2 at 923 K, the silver catalyst restructured to form well-defined surface facets of dimension 1–2 μm. The influence of the restructuring on the oxygen chemisorptive properties of the silver catalyst is discussed. The results of these studies were used to develop a scheme for the interaction of O2 with silver surfaces at 923 K.