The mechanisms of plasma enhanced selective catalytic reduction of NOx on a V2O5-WO3/TiO2-catalyst were investigated for temperatures between 100 °C and 200 °C by applying various analytical methods.In experiments with synthetic gas mixtures containing Ar instead of N2 as a carrier gas the formation of N2 as a main product and thus catalytic reduction of NOx in reactions with NH3 has been proven using mass spectroscopy. More detailed information on the reaction kinetics of NO-formation and removal induced by non-thermal plasmas has been obtained from experiments in gas mixtures containing isotopically marked 15NO. FTIR-absorption spectroscopy was applied to measure the concentrations of 14N- and 15N-containing molecules.Particles formed by the combined plasma- and catalytic treatment of Diesel exhaust with NH3 as reducing agent were analyzed by energy dispersive X-ray scattering. The spectra indicate, that mainly sulfur containing particles were formed. Formation of NH4NO3 plays a minor role. Non-thermal plasma treatment did not show a strong influence on catalytic removal of unburned hydrocarbons, but increased CO-emission was observed.In all experiments plasma induced conversion of NO to NO2 increased NOx-reduction rates.