NOx-Storage Catalyst Systems Designed to Comply with North American Emission Legislation for Diesel Passenger Cars

In this paper we report on a new state of the art diesel LNT (Lean NOx Trap) formulation that is designed to comply with North American emission legislation for diesel passenger cars. Improved performance and durability is demonstrated in an aging study using hydrothermal furnace aging and a prolonged procedure behind the engine consisting of repeated cycles containing sulfur exposure, desulfation and simulated regeneration of a diesel particulate filter. The improved barium based technology shows an increased thermal stability in terms of upper not-to-exceed temperature of at least 50°C. Our data show that potassium based technologies can represent a viable solution for certain applications that require extremely high NOx-conversions at temperatures above 500°C. Potassium based technologies with improved anchoring of the alkali metal show significant reduction in potassium loss to the exhaust gas. After substantial aging on the engine bench the improved Ba-based technology showed NOx conversion of 63% in the FTP75 test cycle. In the fresh state NOx-conversions were some 85%. These conversions were achieved with raw emissions considerably above those values anticipated for the actual US application.