Selective catalytic reduction of NO by NH3 on Cu-faujasite catalysts:: An experimental and quantum chemical approach

The selective catalytic reduction (SCR) of NO by NH3 in the presence of O-2 on Cu-faujasite (Cu-FAU) has been studied. Substitution of some Cu2+ with H+ and Na+ cations, compensating for the negative charge of the zeolite framework forms the various CuHNa-FAU studied. The amount of Cu was held constant and the proportion of H+ and No, varied in the sample. The substitution of Na+ for H+ increases sharply the SCR rate by lowering the temperature of reaction by about 150 K. It is proposed that the rate increase mainly comes from on unhindered migration of Cu from hidden to active sites and a modification of the redox properties of Cu species. The former was demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO. The change in redox properties was demonstrated by a faster oxidation of Cu+ to Cu2+ (rate-determining step). Quantum chemical calculations on model clusters of CuHNa-FAU indicate that the faster rate of oxidation can be explained by a higher lability of protons in the absence of No, which can be then removed from the catalyst more easily to yield H2O during the oxidation process.