Abstract
A kinetic model is developed to predict the influence of temperature and hydrothermal aging on the redox of active Cu sites under standard SCR, NO oxidation and NH3 oxidation conditions over a practically relevant fully-formulated Cu-SSZ-13 catalyst. NO2/N2 production during NO/NH3 titration of CuII sites is utilized to identify rate parameters associated with NO-only RHC (reduction half cycle) and NH3-only RHC respectively. Integral N2 formation during subsequent NO + NH3 titration is consistent with the production of one NO2 per two CuII sites reduced during NO-only RHC and one N2 per six CuII sites reduced during NH3-only RHC. Decreased reduction of CuII sites by NO/NH3 upon hydrothermal aging, along with the production of one NO2 per two CuII sites during NO-only RHC, is accordant with the involvement of proximal ZCuOH and oxygen-bridged dimeric CuII sites. Oxidation of partially solvated and framework coordinated ZCu (CuI) sites occurs in presence of O2, does not produce N2 and can lead to the consumption of Brønsted acid sites. A global OHC kinetic model is developed to predict transient and integral N2 formation during exposure of CuI sites to a mixture of NO and O2. The resulting redox kinetic model quantitatively predicts NO and NH3 consumption during isothermal transient response Cu redox (TRCR) protocols, along with temperature and age dependent steady-state standard SCR and oxidation conditions. The redox model presented in this work synthesizes recent kinetic, spectroscopic and computational findings to provide a foundational description of active site redox during standard SCR, NO oxidation and NH3 oxidation over Cu-SSZ-13.
