High performance of an ultra-low Pt loading diesel oxidation catalyst can be achieved by using a combination of novel nano-array structured support, precise control of ultrafine active Pt particles, and an addition of H-2 as a promoter into the exhausts. Highly stable mesoporous rutile TiO2 nano-array was uniformly grown on threedimensional (3-D) cordierite honeycomb monoliths using a solvothermal synthesis. Atomic layer deposition was employed for precise dispersion of ultrafine Pt particles (0.95 +/- 0.24 nm) on TiO2 nano-array with a Pt loading of 1.1 g/ft(3). Despite low Pt loading, the Pt/TiO2 nano-array catalyst shows impressive low-temperature oxidation reactivity, with the conversion of CO and total hydrocarbon (THC) reaching 50% at 224 and 285 degrees C, respectively, in the clean diesel combustion (CDC) simulated exhaust conditions. The excellent activity is attributed to the unique nano-array structure that promotes gas-solid interaction and ultra-small Pt particle dispersion that increase surface Pt atoms. We also demonstrate that addition of more H2 into the exhaust can lower light-off temperature for CO and THC by up to similar to 60 degrees C and similar to 30 degrees C, respectively.