Flow reactor experiments and kinetic modeling have been performed in order to study the mechanism and kinetics of NO x reduction over Pt/SiO 2 catalysts with hydrogen as the reducing agent. The experimental results from NO oxidation and reduction cycles showed that N 2 O and NH 3 are formed when NO x is reduced with H 2 . The NH 3 formation depends on the H 2 concentration and the selectivity to NH 3 and N 2 O is temperature dependent. A previous model has been used to simulate NO oxidation and a mechanism for NO x reduction is proposed, which describes the formation/consumption of N 2 , H 2 O, NO, NO 2 , N 2 O, NH 3 , O 2 and H 2 . A good agreement was found between the performed experiments and the model.