An in situ FTIR study of the plasma- and thermally-driven reaction of isopropyl alcohol at CeO2: evidence for a loose transition state involving Ce3+?

Abstract

This paper reports on the thermally-driven and non-thermal plasma-driven reaction of IsoPropyl Alcohol (IPA) on ceria (CeO₂) with the aim to investigate the differences between plasma catalytic interactions and the analogous thermal reactions. Both were studied by in situ infrared spectroscopy: using diffuse reflectance for the thermal reaction and reflectance infrared for the plasma. For the thermal reaction, the activity towards the formation of acetone and acetaldehyde and, at higher temperatures, CO₂ was dependent upon the coverage of surface carbonates and bicarbonates, suggesting at least some of these species blocked the relevant active sites. However, for the first time, methane and cold CO was observed and this was interpreted in terms of a roaming mechanism taking place at the surface via a loose transition state. By contrast, the plasma-driven process was not inhibited by adsorbed carbonaceous species producing acetone followed by isophorone and a polymethylacetylene-like polymer. Comparisons are made between the equivalent thermal and plasma reactions of isopropyl alcohol on Macor and tin oxide surfaces. On Macor the plasma produced similar products whereas on tin oxide there was no reaction. This suggests that the selection of catalysts for plasma processing cannot necessarily be determined from the equivalent thermal process.