posted on 2021-10-13, 23:44authored byLeila Negahdar, Naomi E. Omori, Matthew G. Quesne, Mark D. Frogley, Fernando Cacho-Nerin, Wilm Jones, Stephen W. T. Price, C. Richard A. Catlow, Andrew M. Beale
Unwanted N2O formation is a problem that has been noted
in selective catalytic reduction (SCR) where copper zeolite catalysts
are utilized. With its immense global warming potential and long-term
stability, elevated atmospheric N2O has already been identified
as a future challenge in the war on climate change. This paper explores
the phenomenon of N2O formation during NH3-SCR
over Cu-SSZ-13 catalysts, which are currently commercialized in automotive
emissions control systems, and proposes a link between N2O production and the local copper environment found within the zeolite.
To achieve this, a comparison is made between two Cu-SSZ-13 samples
with different copper co-ordinations produced via different synthesis
methods. A combination of synchrotron X-ray absorption near-edge spectroscopy,
UV–vis, Raman, and density functional theory (DFT) is used
to characterize the nature of copper species present within each sample.
Synchrotron IR microspectroscopy is then used to compare their behavior
during SCR under operando conditions and monitor
the evolution of nitrate intermediates, which, along with further
DFT, informs a mechanistic model for nitrate decomposition pathways.
Increased N2O production is seen in the Cu-SSZ-13 sample
postulated to contain a linear Cu species, providing an important
correlation between the catalytic behavior of Cu-zeolites and the
nature of their metal ion loading and speciation.