Gas treatment device, methods for making and using the same, and a vehicle exhaust system

Gas treatment devices and vehicle exhaust systems are disclosed herein. In one embodiment, the vehicle exhaust system, comprises: an engine, a gas treatment device disposed downstream from the engine, the gas treatment device comprising a housing, a substrate disposed within the housing, the substrate comprising a catalyst and a hexaaluminate comprising a catalyst stabilizer disposed in a hexaaluminate crystal structure.