The use of concentration-transient methods in the elucidation of deNO(x) mechanisms over supported Pt catalysts is discussed with reference made to non steady state (TAP, reactant removal, NSSITKA) and steady state (SSITKA) techniques. The reaction systems studied include the NO/C3H6/O-2, NO/C3H8/O-2, NO/H-2/O-2 and NO/H-2 reactions over supported Pt catalysts (Al2O3 and SiO2) and Al2O3. The use of concentration-transient techniques can give information about the presence, concentration and reactivity of adsorbed surface intermediates. Extrapolations from concentration-transient techniques are then used to give information about Various mechanistic steps on the catalysts involved in the conversion of reactants to products. This information can then be used to get a clearer understanding of how and why certain catalysts are active (inactive) for the reduction of NOx under lean burn conditions.