Restricting The Growth Of Pt Nanoparticles Through Confinement In Ordered Nanoporous Structures

Accelerated aging of Pt diesel oxidation catalysts at 800 degrees C in the air causes vapor-phase emission of PtO2 leading to severe deterioration in catalyst activity. Here we show that the growth of Pt nanoparticle size can be restricted by locating the Pt within nanosized pores. The mechanism of Pt sintering within the pores changes from vapor phase transport to surface diffusion because the pore volume is rapidly saturated with gas-phase PtO2. This causes Pt particle growth within the pores to be restricted. Knudsen diffusion helps to slow the rate of Pt emission compared to an open-pore silica gel. However, the PtO2 that escapes from the pores grows to micronsized particles, leading to loss of activity. The Pt retained in the pores grows large enough to block access to gasphase reactants. These results provide insights for the design of pore structures to improve the durability of exhaust emission catalysts.