Non-thermal plasma assisted NOx storage and reduction over a cobalt-containing Pd catalyst using H2 and/or CO as reductants

Abstract

A catalyst of the type Pd/Co/Ba/Al was examined for lean NOx trap (LNT) applications, and compared with Pd/Ba/Al and Pt/Ba/Al reference catalysts for NOx storage and reduction using H2 and/or CO as reducing agents. The activity of Pt/Ba/Al was greatly depressed when using CO as reductant at low temperatures owing to the strong poisoning effect of CO on Pt. The Pd/Co/Ba/Al catalyst exhibited higher activity for NO oxidation to NO2 and better NOx storage capacity than Pt/Ba/Al and Pd/Ba/Al catalysts, also showed higher NOx reduction activity with CO compared to the other two catalysts. However, it shows relatively low NOx removal efficiency below 250°C, especially using CO as reductants, indicating that regeneration of stored NOx is the rate limiting step. By employing non-thermal plasma in the rich phase to assist reduction of the stored NOx, the Pd/Co/Ba/Al sample exhibited excellent NOx removal efficiency under plasma assisted lean/rich cycling conditions, affording NOx conversions close to 99% over a broad temperature window of 150–350°C, even when using CO as the reducing agent.