Characterization of copper species over Cu/SAPO-34 in selective catalytic reduction of NOx with ammonia: Relationships between active Cu sites and de-NOx performance at low temperature

► We prepare a series of Cu/SAPO-34 catalysts with varying Cu loadings. ► We identify and quantify four coexisting copper species in these samples. ► The isolated Cu2+ species are the active sites for NH3-SCR reaction at T < 200 °C. ► The formation of external surface CuO complex sacrifices isolated Cu2+ ions.