Atomically Controllable Pd@Pt Core-Shell Nanoparticles towards Preferential Oxidation of CO in Hydrogen Reactions Modulated by Platinum Shell Thickness

The shell-thickness effect of Pd@Pt core-shell nanoparticles (NPs) towards the preferential oxidation of CO in the presence of excess H-2 (PROX) was investigated. Atomically controllable Pd@Pt core-shell nanoparticles were fabricated by using an area-selective atomic layer deposition (ALD) method. A linear growth rate of Pt on a Pd surface monitored with in situ quartz crystal microbalance indicated that the shell thickness could be controlled by varying the number of ALD cycles. The core-shell Pd@ Pt NPs showed better activity and selectivity than monometallic NPs. The catalyst with a monolayer Pt shell showed optimal performance and minimal Pt loading. The mechanism of the Pt shell on Pd core catalyzed PROX reactions was studied by DFT simulations. The energy barriers to CO oxidation significantly decreased upon coating the catalyst with Pt, which led to enhanced activity and selectivity, and Pd/Pt-1 (monolayer) showed the lowest barrier.