A process and catalysts therefor are detailed which will selectively remove 100% of the NOX in a waste effluent (flue gas) also containing oxygen. The process functions on the basis of an adsorbent which efficiently adsorbs the NOX at high space velocities and for long periods (over 9 h). Temperature of adsorption is a very practical 180 degrees C or above. The catalyst adsorbent can be regenerated for reuse repeatedly by exposing to a gas containing 0.5-10% Hg at 250 degrees C or above. A cycle of use-regeneration is contemplated for commercial exploitation. Any NOX not reduced as it is desorbed from the adsorbent is reduced to N-2 + H2O in a downstream catalyst bed thus eliminating 100% of the inlet NOX.