Sn-modified NOX storage/reduction catalysts

Ba-, K-, and Ba–K-based NOX storage/reduction (NSR) catalysts were prepared, with and without Sn as a promotor. Catalysts and catalyst/soot mixtures were evaluated for NOX reduction and soot oxidation under standard NSR cycling conditions. The activity study was accompanied by dispersion measurements, TEM, XRD, and XPS characterization. It was found that modification with Sn did not significantly influence NOX adsorption, however, Sn notably enhanced soot oxidation for Ba-based systems. This was correlated to Pt oxidation state modification. Also the addition of Sn to the Pt–Ba and Pt–Ba–K catalysts lowered the onset temperature of S release. The Pt–Ba–K catalyst had higher stability against S-poisoning, likely due to the preferential adsorption of S onto K-species, partially maintaining Ba sites for NOX trapping.

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► Sn-promoted standard NSR catalyst showed enhanced soot oxidation.
► The NOX storage capacities were not affected by Sn addition.
► Sn lowered the onset temperature of S release.