Coherent X-ray Imaging of CO-Adsorption-Induced Structural Changes in Pt Nanoparticles: Implications for Catalysis

Abstract

Using coherent X-ray diffraction imaging (CXDI) as an in situ tool, we determined the shape and strain state of a platinum nanoparticle with ≈160 nm diameter supported by a strontium titanate substrate. The experiment was performed at a temperature of 400 K under continuous gas flow conditions of pure Ar and Ar/CO mixtures. The nanoparticle was preselected by scanning electron microscopy (SEM) and postanalyzed by atomic force microscopy (AFM). We obtain a very good agreement between the overall nanoparticle size, shape, and defect structure as determined by CXDI and AFM. In addition, we compare the strain state in the nanoparticle near surface region and its bulk: For pure Ar flow, we find a slight compressive strain in the nanoparticle bulk compared to an expansion in the near surface region. We ascribe the latter to the presence of high index vicinal surfaces. Our analysis suggests that under mixed Ar/CO flow at 400 K reshaping of the nanoparticle occurred. New high index facets developed, leading to a stronger lattice expansion, also propagating into the nanoparticle bulk. Our high-resolution experiments pave the way for future CXDI experiments under operando catalytic reaction conditions.