This study demonstrated that a plasma-catalyst system using Pt catalyst provides high performance for NO decomposition under a humidified condition. In this work, we optimized the catalyst using various supported metals, oxides, and investigated the effects of the loading amount of metal and imposed voltage of plasma for highly efficient NO conversion. Results show that Pt is the most active metal and that it promotes formation of N-2 and N2O from NO, and that N2O was an intermediate of N-2 formation from NO over Pt. Regarding the effect of support, Pt catalysts supported on SiO2 and Al2O3, showed higher activity. We investigated the effects of metallic surface area of Pt and imposed voltage. Results show that both the energy input and metallic surface area of Pt plays important roles for NO decomposition to N-2 in the plasma-catalyst system. The maximum peak current in plasma is extremely important. (C) 2013 Elsevier B.V. All rights reserved.