Recent NH3-SCR Mechanism Research over Cu/SAPO-34 Catalyst

The preliminary mechanism research of NH3-SCR and NH3 oxidation over Cu/SAPO-34 catalyst is explored. The XRD, SEM, in situ EPR, NH3-SCR, NH3 oxidation test, DRIFTs, and the kinetic tests were performed for the bulk characterization, catalytic activity measurement, and the mechanism estimation. The NH3-SCR result showed that Cu/SAPO-34 revealed excellent activity during 120-600 degrees C, while the NH3 oxidation appeared above 300 degrees C and caused the decline of NO conversion. The order of various reactants (NO, NH3, and O-2 for NH3-SCR and NH3, O-2, for NH3 oxidation) was estimated by the kinetic tests to explain their behaviors during the NH3-SCR process. The NH3-SCR presents strong dependence on adsorbed NH3 species on Cu/SAPO-34, but the NH3 oxidation does not. Furthermore, the EPR experiment proved that the isolated Cu2+ species are the active sites and the ammonia nitrites species are the intermediate for NH3-SCR over Cu/SAPO-34 catalysts. The different behavior of adsorbed NH3 species in NH3-SCR and NH3 oxidation was studied through DRIFTs to explain the competition between the two reactions for NH3 consumption at high temperature. Meanwhile, combining the results of previous research, the primary reaction mechanism over Cu/SAPO-34 during the NH3-SCR process was conducted.