Patent ID: 7199078

Claim:
A method of increasing the sulfur tolerance of a nitrogen oxide trap, the method comprising: a) preparing a mixed oxide solution containing a water soluble calcium compound and a water soluble magnesium compound; b) coating said nitrogen a sulfur oxide trap with the mixed oxide solution to form a coated nitrogen oxide trap; c) drying the coated nitrogen oxide trap at a first elevated temperature; and d) heat treating the coated nitrogen oxide trap at a second elevated temperature to form a modified NOx trap overcoated with a mixed oxide layer wherein the second elevated temperature is higher than the first elevated temperature and the mixed oxide layer does not completely cover the NOx trap; wherein the modified NOx trap when placed downstream of a catalytic convener in an exhaust system of an internal combustion engine, the modified NOx trap is regenerable by operating the internal combustion engine system under stoichiometric or rich fuel conditions for a sufficient time that the modified NOx oxide trap achieves a temperature of at least 450° C.