Promoted Platinum Catalytic Activity and Thermal Stability with Nano-Scale Cobalt Oxide Coating via Atomic Layer Deposition

Platinum nanoparticles (NPs) play an important role in the catalytic conversion of automotive exhaust. The catalytic performance is closely related to the number of active sites. One drawback of platinum catalyst is its tendency towards sintering under high temperatures which may occur during high engine loads. Sintering of Pt NPs will cause larger particles formation and a decrease in the number of active sites. ^[1]

Many methods have been tried to form core shell structures to encapsulate the metal nanoparticles with porous materials to minimize sintering.^[2] The nanoparticles with a protective shell show good sintering resistance.^[3] However in some cases the catalysis performance decreases because the thick protective shell blocks the access of the reactants. New methods are needed to improve the controllability of the coating layer thickness and structure to stabilize the metal nanoparticles and at the same time maintain the catalysis performance. Atomic layer deposition (ALD) shows it unique advantages in sub-nanometer thin film thickness control due to the self-limiting growth nature.^[4] Recent works encapsulate the palladium nanoparticles with porous Al₂O₃ through ALD that effectively prevents sintering and coking in the ethane oxidation reactions.^[5]

Here we report the use of active oxide layer to coat the platinum NPs for CO oxidation. Our results indicate that with proper thickness control of the coating layer the catalysts have good thermal stability. At the same time the platinum and the active ingredients in the oxide layer may also form alloy particles, further promoting the total catalysis performance.

Reference

[1] M A Asoro, D Kovar, Y Shao-Horn, P J Ferreira, Nanotechnology 21 (2010)

[2] Zhao M, Sun L, Crooks RM, J. Am. Chem. Soc. 120 (1998)

[3] Z Ma, S. Brown, J.Y. Howe, S.H Overbury, S Dai, J. Phys. Chem. C 112 (2008)

[4] Riikka L. Puurunen, J. Appl. Phys. 97, 121301 (2005)

[5] Lu. J. L, Fu. B. S, Kung, M.C, J W Elam, P C Stair, Science 8, 2405 (2012)