Plasma Enhanced Selective Catalytic Reduction: Kinetics of NOx-Removal and Byproduct Formation

The mechanisms of plasma enhanced selective catalytic reduction of NO_x 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 NO_x 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 NO_x-reduction rates.