In the USA, hydrogen sulfide emissions from three-way catalytic converter-equipped automobiles are effectively suppressed by the addition of nickel to catalyst formulations. This approach is generally not utilized in catalyst formulations for Europe because of European concern about the health, safety and environmental issues surrounding the use of nickel. A modified form of iron oxide has been identified which suppresses hydrogen sulfide emissions from three-way catalysts. This suppression has been achieved without affecting the fresh or aged performance of the catalyst, a problem often encountered with other materials. The performance and durability of catalyst formulations incorporating the new material are demonstrated with a variety of aging and evaluation protocols.