Trapping of Mobile Pt Species by PdO Nanoparticles under Oxidizing Conditions

Abstract

Pt is an active catalyst for diesel exhaust catalysis but is known to sinter and form large particles under oxidizing conditions. Pd is added to improve the performance of the Pt catalysts. To investigate the role of Pd, we introduced metallic Pt nanoparticles via physical vapor deposition to a sample containing PdO nanoparticles. When the catalyst was aged in air, the Pt particles disappeared, and the Pt was captured by the PdO, forming bimetallic Pt-Pd nanoparticles. The formation of metallic Pt-Pd alloys under oxidizing conditions is indeed remarkable but is consistent with bulk thermodynamics. The results show that mobile Pt species are effectively trapped by PdO, representing a novel mechanism by which Ostwald ripening is slowed down. The results have implications for the development of sinter-resistant catalysts and help explain the improved performance and durability of Pt-Pd in automotive exhaust catalytic converters.

Platinum Inhibits Low‐Temperature Dry Lean Methane Combustion through Palladium Reduction in Pd−Pt/Al2O3: An In Situ X‐ray Absorption Study

“…As expected, [39] the addition of palladium to platinum preventedi ts excessive sintering, which also can be seen in the TEM images of the calcined catalysts ( Figure 1). Ar icher palladium content of the catalysts resultsi nal ower degree of sintering.…”

Trapping mobile Pt species by PdO in diesel oxidation catalysts: Smaller is better

“…[3]When Pt nanoparticles were deposited on a planar model SiO 2 supportas a separate phase, heating for only 2 minutes at 650 °C in air caused the formation of bimetallic PtPd particles. [7] This previous work demonstrates that Pt species are mobile andcan be effectively trapped by PdO at high temperatures in air, forming bimetallic PtPd particleswhich are thermodynamically more stable. [7] The migration and vapor phase transport of precious metals in automotive exhaust catalysts has been documented in the literature.…”

Three‐Dimensional Probing of Catalyst Ageing on Different Length Scales: A Case Study of Changes in Microstructure and Activity for CO Oxidation of a Pt–Pd/Al2O3 Catalyst

“…Previous studies have shown that Pt is very mobile at high temperatures in oxidising environments and can be effectively trapped by PdO nanoparticles ,. The studies demonstrated that upon heat treatment of specimens with initially separated Pt and PdO nanoparticles, the highly mobile Pt is trapped by the more stable PdO nanoparticles and alloyed Pt–Pd nanoparticles are formed, which are thermodynamically more stable and slow down further sintering by Ostwald ripening as well as the emission of Pt into the vapour phase .…”