NOx reduction to N2 with commercial fuel in a real diesel engine exhaust using a dual bed of Pt/beta zeolite and RhOx/ceria monolith catalysts

Abstract

The Selective Catalytic Reduction (SCR) of NOx has been performed in a real diesel engine exhaust using commercial diesel fuel as a reducing agent and a dual bed catalytic system consisting of a Pt/beta zeolite/honeycomb monolith SCR catalyst located upstream a N2O decomposition RhOx/Ce0.9Pr0.1O2/honeycomb monolith catalyst. Cordierite honeycomb monoliths (diameter 2.3 cm; length 7.5 cm; 400 cpsi) were washcoated with beta zeolite and 1% platinum (on zeolite basis) was impregnated afterwards. The effect of the beta zeolite slurry viscosity on the dip-coating process was studied in detail, concluding that slurries with viscosity ≤23 mPa s must be used, otherwise the zeolite suspension was not able to penetrate into the monolith channels. The dip-coating method was optimized for the Pt/beta zeolite/honeycomb monolith preparation. The RhOx/Ce0.9Pr0.1O2/honeycomb monolith catalyst, used for N2O decomposition, was prepared by nitrate precursor decomposition. The maximum NOx removal achieved with the Pt/beta zeolite/honeycomb monolith was 50% at 350 °C. The production of N2O as undesired NOx reduction product, which is a drawback of platinum SCR catalysts, has been solved by using the dual bed configuration, where both monolith catalysts operated at the same temperature, and 100% N2 selectivity has been obtained.