Mobility of Cu Ions in Cu-SSZ-13 Determines the Reactivity of Selective Catalytic Reduction of NO_x with NH₃

Abstract

Selective catalytic reduction of NO x with NH 3 (NH 3 − SCR) in Cu-SSZ-13 has been proposed to have a unique homogeneouslike mechanism governed by the spatial proximity of mobile Cu ions. Among factors that determine the proximity, the effect of ion density on the SCR reaction is well established; however, it has not been verified how the different mobility of the Cu ion influences the SCR reaction. Herein, we try to reveal the mobility-dependent SCR reaction by controlling the Cu species with different ion mobilities in Cu-SSZ-13. Since the reaction kinetics is governed by the diffusion of Cu ions, the Cu ion mobility determines the reactivity of the Cu-SSZ-13. In terms of this correlation, enhanced ion mobility leads to improved NH 3 −SCR activity. These findings help understand the behavior of Cu ions in Cu-SSZ-13 under a catalytic reaction and provide insights to design rational catalysts by tuning the ion mobility.

Analogous Mechanistic Features of NH3-SCR over Vanadium Oxide and Copper Zeolite Catalysts

“…V- and Cu-based catalysts have been thoroughly investigated for NH 3 -SCR at the molecular level over the past four decades. − Although the mechanism of NH 3 -SCR with these catalysts has been separately discussed, a detailed literature survey suggests mechanistic similarities between V − and Cu − catalysts, as well as common unresolved issues regarding the NH 3 -SCR mechanism. The common features of the NH 3 -SCR mechanisms featuring V and Cu catalysts are depicted in Figure A,B.…”

Review of the application of Cu-containing SSZ-13 in NH3-SCR-DeNOx and NH3-SCO

“…51,161,175 The mobility of the Cu ions ( i.e. , one [Cu I (NH 3 ) 2 ] + must migrate to the vicinity of another; enhanced in the presence of H 2 O 176–178 ) guarantees the formation of these dimeric Cu species, 90,166 thus improving the NH 3 -SCR-DeNO x activity. The 1Al–Cu species (located at isolated single Al sites, i.e.…”

“…179,180 The ratio of n (1Al–Cu)/ n (2Al–Cu) can be controlled through the catalyst's hydrothermal aging. 90 Krishna et al 181 suggested their perspective that spatial proximity of active Cu sites is required in the redox cycle of Cu 2+ /Cu + . Such proximity assists the oxidation of NH 3 -solvated Cu + ions to form dimeric Cu intermediates [Cu I (NH 3 ) 2 ] + –O 2 –[Cu I (NH 3 ) 2 ] + .…”

Unusual water-assisted NO adsorption over Pd/FER calcined at high temperatures: The effect of cation migration

“…[24][25] Copper ions bound to cationic sites become mobile when they are solvated by water ligands and migrate from cage to cage, making the formation of copper dimers, necessary for re-oxidation in the selective catalytic reduction (SCR), facile. [26][27][28][29][30] In contrast, water is an obstacle in palladium ion exchanged zeolites used as passive NOx adsorbers (PNA) at low temperatures. [31][32][33][34][35][36][37] In zeolite-based PNAs (SSZ-13, ZSM-5, BEA) Pd ions efficiently trap NO in nitrosyl complexes, i.e., Pd 2+ -NO.…”