Strikingly distinctive NH<sub>3</sub>-SCR behavior over Cu-SSZ-13 in the presence of NO<sub>2</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 35941128.
- Also identified by DOI 10.1038/s41467-022-32136-z and PMC identifier 9360435.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the standard selective catalytic reduction (SCR) of NO with NH<sub>3</sub>. However, their activity is unexpectedly inhibited in the presence of NO<sub>2</sub> at low temperatures. This is strikingly distinct from the NO<sub>2</sub>-accelerated NO<sub>x</sub> conversion over other typical SCR catalyst systems. Here, we combine kinetic experiments, in situ X-ray absorption spectroscopy, and density functional theory (DFT) calculations to obtain direct evidence that under reaction conditions, strong oxidation by NO<sub>2</sub> forces Cu ions to exist mainly as Cu<sup>II</sup> species (fw-Cu<sup>2+</sup> and NH<sub>3</sub>-solvated Cu<sup>II</sup> with high CNs), which impedes the mobility of Cu species. The SCR reaction occurring at these Cu<sup>II</sup> sites with weak mobility shows a higher energy barrier than that of the standard SCR reaction on dynamic binuclear sites. Moreover, the NO<sub>2</sub>-involved SCR reaction tends to occur at the Brønsted acid sites (BASs) rather than the Cu<sup>II</sup> sites. This work clearly explains the strikingly distinctive selective catalytic behavior in this zeolite system.