An automobile exhaust system includes a catalytic converter, a NOx trap, and a sulfur oxide trap. The sulfur oxide trap improves the efficiency of the NOx trap. Sulfur oxide has a deleterious effect on the performance of nitrogen oxide traps. The sulfur oxide trap comprises a monolithic substrate which is over-coated with an aluminum oxide layer and a mixed oxide layer of calcium oxide and magnesium oxide. In a variation, a sulfur oxide trap is integrated with a nitrogen oxide trap by coating the catalyst contained within a nitrogen oxide trap with a mixed oxide layer of calcium oxide and magnesium oxide. In each embodiment, the sulfur oxide trap can be regenerated by heating at elevated temperature for a short time period.