The effects of photocatalysis and thermocatalysis in surface discharge type plasma reactors combined with TiO2- and Al2O3-based catalysts were analyzed. The photocatalytic decomposition of acetaldehyde was not observed although the TiO2 absorbed the UV light (300 < lambda < 380 nm) emitted from N-2 plasma. The intensity of UV emission from plasma decreased with increasing O-2 concentration. In atmospheric air, the photocatalytic decomposition rate by UV light of plasma is lower than 0.2% of the decomposition rate by the plasma itself. The coating of gamma-Al2O3 on the inside wall of plasma reactor improved the oxidation rate for CO by a factor of 3.5, while TiO2 improved by only a factor of 1.8, compared with the bare plasma reactor. The high activity of Al2O3 seems to be due to the active oxygen species produced by the O-3 decomposition. (c) 2005 Elsevier B.V. All rights reserved.