Journal
ACS CATALYSIS
Volume 7, Issue 12, Pages 8214-8227Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.7b03020
Keywords
selective catalytic reduction; Cu/SSZ-13; hydrothermal aging; EPR; NMR; TEM; DRIFTS
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Funding
- U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office
- DOE's Office of Biological and Environmental Research
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The hydrothermal stability of Cu/SSZ-13 SCR catalysts has been extensively studied, yet atomic-level understanding of changes to the zeolite support and the Cu active sites during hydrothermal aging are still lacking. In this work, via the utilization of spectroscopic methods including solid-state Al-27 and Si-29 NMR, EPR, DRIFTS, and XPS, together with imaging and elemental mapping using STEM, detailed kinetic analyses, and theoretical calculations with DFT, various Cu species, including two types of isolated active sites and CuO clusters, were precisely quantified for samples hydrothermally aged under varying conditions. This quantification convincingly confirms the exceptional hydrothermal stability of isolated Cu2+-2Z sites and the gradual conversion of [Cu(OH)](+)-Z to CuOx clusters with increasing aging severity. This stability difference is rationalized from the hydrolysis activation barrier difference between the two isolated sites via DFT. Discussions are provided on the nature of the CuOx clusters and their possible detrimental roles on catalyst stability. Finally, a few rational design principles for Cu/SSZ-13 are derived rigorously from the atomic-level understanding of this catalyst obtained here.
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