Abstract A dispersed phase of barium oxide (BaO) supported on alumina has been shown to be primarily responsible for NO x storage in practical lean NO x trap catalysts. Conventional impregnation based catalyst loading techniques generate a mixture of dispersed and less active bulk-like BaO phases on alumina, with the bulk-like phase increasing as weight loading increases. Samples of equivalent BaO weight loading on fused alumina were prepared by successive ionic layer deposition (SILD) and wet impregnation. NO 2 temperature programmed desorption experiments demonstrate that SILD is uniquely capable of selectively synthesizing uniform, nanodispersed BaO rafts with high surface coverage. These nanodispersed SILD structures show remarkable thermal stability under high operating temperatures up to 650 °C.