Effects of Cu Density in Cu-SSZ-13 Zeolites on Low- Temperature NOx Selective Catalytic Reduction with NH3

摘要

NOx selective catalytic reduction (SCR) using NH3 as a reductant over Cu-SSZ-13 zeolites is a commercial technology used to meet emissions targets in lean-burn and diesel exhaust. Low temperature (473 K) NOx SCR on Cu-SSZ-13 occurs via a Cu(II)/Cu(I) redox cycle [1] on two types of isolated Cu sites, both divalent Cu~(2+) cations compensating paired framework Al atoms and monovalent [CuOH]~+ complexes at isolated framework Al atoms, which are solvated by NH3 during reaction [2]. Both types of cationic Cu sites were identified by infrared, UV-Visible and operando X-ray absorption (XAS) spectroscopies and also from their exchange stoichiometry with surface protons, the residual number of which was quantified by NH3 titration.