Elucidating the surface compositions of Pd@PtnL core–shell nanocrystals through catalytic reactions and spectroscopy probes

Abstract

The catalytic behaviors or properties of bimetallic catalysts are highly dependent on the surface composition, but it has been a grand challenge to acquire such information. In this work, we employ Pd@Pt_nL core–shell nanocrystals with an octahedral shape and tunable Pt shell thickness as a model system to elucidate their surface compositions using catalytic reactions based upon the selective hydrogenation of butadiene and acetylene. Our results indicate that the surface of the core–shell nanocrystals changed from Pt-rich to Pd-rich when they were subjected to calcination under oxygen, a critical step involved in the preparation of many industrial catalysts. The inside-out migration can be attributed to both atomic interdiffusion and the oxidation of Pd atoms during the calcination process. The changes in surface composition were further confirmed using infrared and X-ray photoelectron spectroscopy. This work offers insightful guidance for the development and optimization of bimetallic catalysts toward various reactions.