Regulation of Al distributions and Cu2+ locations in SSZ-13 zeolites for NH3-SCR of NO by different alkali metal cations

Abstract

Different types of alkali metal cations (Li+, Na+, K+ and Cs+) were used as counter-cations to synthesize SSZ-13 for improving its catalytic performance for selective catalytic reduction (SCR) of NO by NH3. The Al distribution and Cu2+ locations in the framework of SSZ-13 were investigated by DR UV–vis, 27Al and 29Si MAS NMR, ESR, NH3– and CO-adsorbed DRIFT spectroscopies. It is shown that paired Al species and distorted AlO4- tetrahedra both increase with decreasing radii of alkali metal cations, which leads to an increase of isolated Cu2+ species and an enhancement of NH3-SCR catalytic performance. Surprisingly, some Cu(OH)+ species was transformed into isolated Cu2+ species when the sample was treated at 800 °C for 12 h in low-content H2O/air despite of occurrence of a slight dealumination in the framework. The isolated Cu2+ species is demonstrated to show higher catalytic activity than Cu(OH)+ species and Cu2+ species adsorbed on Al2O3 species.