Atomic-Scale STEM Analysis Shows Structural Changes of Au–Pd Nanoparticles in Various Gaseous Environments

Abstract

We report dynamical restructuring effects in free-standing Au0.75Pd0.25 nanoparticles occurring in gaseous environments at elevated temperatures. The freshly prepared sample was found to have a core–shell structure with a Pd-rich phase on the surface. The evolution of sample composition and morphology under exposure to 1 bar of pure gases, namely O2, H2, air, CO, and CO2, at different temperatures was studied using in situ scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS). We observed sharper facets on the surface of the particles under O2 or air at 400 °C. Small islands of Pd were present on the surface, although some Pd was redistributed inside the bulk when the temperature was increased under O2. Subtle changes in surface roughness were noted when O2 was substituted with H2 at 400 °C, an observation correlated to density functional theory (DFT) calculations. The particles lost clean surface facets when CO was introduced at room temperature and at 200 °C. No substantial changes could be observed after exposure to CO2 at 250 °C. The adsorption of CO molecules on the surface modifies the surface of the particles and decreases the facet prevalence. These in situ observations show how gases can induce subtle modification of the surface of nanocatalysts, potentially impacting their chemical properties.

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

“…We qualitatively observed a higher NP density and thus, shorter average interparticle distance, in the dense catalysts, as expected (Figure a). The calcination treatment to remove the templating colloids and create macroporosity also induced homogeneous alloying of the bimetallic NPs as confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX, Figure b), consistent with previous reports. − For all figures throughout this work, we present data from the sparse (s) and dense (d) catalysts in lighter and darker colors, respectively.…”

Regulating and identifying the structures of PdAu alloys with splendid oxygen reduction activity for rechargeable zinc–air batteries

“…The reduction in the nanoparticle size was attributed to the insulation effect of introduced Au, which possessed smaller surface free energy than Pd. 11,19 In support of this, Au 100 exhibited uniformly distributed ∼5 nm nanoparticles on its surface (Fig. S11 and Table S1, ESI†).…”

Influence of Pd Concentration in Au–Pd Nanoparticles for the Hydrogenation of Alkynes

“…To be clear, this is not an artifact of microscope focus due to the small depth of field: a through focal series did not make a difference. One can also hypothesize that the incorporation of Pd into Au increasingly changes the lattice parameter, destabilizing the energetic driving force that causes the formation of the icosahedral structure. − The trend is even more visible for Pd 0.25 Au 0.75 particles.…”