In
this work, a kinetic model is developed for the reduction of
CuII sites by NO + NH3 and the reoxidation of
NH3-solvated CuI sites by O2 and
NO in Cu-SSZ-13. Fourier transform infrared (FTIR) spectroscopy and
spatially resolved capillary inlet mass spectrometry (SpaciMS) measurements
during transient reactor experiments are utilized to identify the
rate parameters associated with NO + NH3 RHC (reduction
half-cycle), proposed to occur via two distinct pathways involving
adsorbed NH3 and gas-phase NH3. The resulting
NO + NH3 RHC model is validated using spatiotemporal N2 measurements covering a wide range of temperatures (200–450
°C) and space velocities (53 000–640 000
h–1). N2O formation is observed and modeled
during NO + NH3 RHC, with quantitative validation under
standard selective catalytic reduction (SCR) conditions. Experimentally
measured enthalpic and entropic changes associated with O2 adsorption on NH3-solvated CuI (ZCu(NH3)2) complexes [KamasamudramK.
Kamasamudram, K.
Catal. Today2010151212222], along with activation
energies estimated computationally for the intercage diffusion of
ZCu(NH3)2 complexes [PaolucciC.
Paolucci, C.
Science2017357898903], are incorporated into a mean field kinetic model for the low-temperature
oxidation half-cycle (OHC). Significant NH3 release is
observed during the isothermal oxidation of CuI sites,
attributed to desorption of NH3 ligands from NH3-solvated CuII dimers (Z2Cu2(NH3)4O2). Reduction of these dimeric complexes
leads to the consumption of one NO/CuII, contradicting
the expected reduction stoichiometry. Inclusion of a global Arrhenius
rate for the NO titration of Z2Cu2(NH3)4O2 complexes provides accurate representations
of standard SCR on reduced and oxidized catalysts, predicting transient
NO and NH3 consumption between 150 and 250 °C as a
function of hydrothermal aging. Deactivation of low-temperature standard
SCR by NH3 is observed at high NH3 pressures,
modeled via the formation of superoxo amino (ZCu(NH3)3OO*) complexes during NH3 titration of Z2Cu2(NH3)4O2 complexes
[NegriC.
Negri, C.
J. Am. Chem. Soc.20201421588415896]. The redox kinetic model presented here provides a foundational
description of active site redox during low-temperature standard SCR,
combining the recent kinetic, spectroscopic, and computational findings
on the mechanism of standard SCR over Cu-SSZ-13.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.