Electrocatalytic denitrification is a promising technology for removing NOx species  (NO3 - , NO2 - and NO). For NOx electroreduction (NOxRR), there is a desire for  understanding the catalytic parameters that control the product distribution. Here, we elucidate selectivity and activity of catalyst for NOxRR. At low potential we classify metals by the binding of ?NO versus ?H. Analogous to classifying CO2 reduction by CO vs?H, Cu is able to bind?NO while not binding ?H giving rise to a selective NH3 formation. Besides being selective, Cu is active for the reaction found by an activity-volcano. For metals that does not bind NO the reaction stops at NO, similar to CO2-to-CO. At potential above 0.3 V vs RHE, we speculate a low barrier for N coupling with NO causing N2O formation. The work provide a clear strategy for selectivity and aims to inspire future research on NOxRR.