Aberration‐Corrected Transmission Electron Microscopy and In Situ XAFS Structural Characterization of Pt/γ‐Al₂O₃ Nanoparticles

Abstract

Aberration‐corrected (AC) STEM, AC TEM and in situ X‐ray absorption fine structure spectroscopy (XAFS) were used to characterize the Pt clusters present on a 0.35 wt % Pt on γ‐alumina support after reduction in hydrogen at 700 °C. STEM high‐angle annular dark field imaging shows that cluster formation takes place at temperatures up to approximately 350 °C, and this is followed by gradual growth in cluster size for heat treatments in hydrogen up to 700 °C. The STEM data show that after 700 °C reduction the Pt clusters are present in a narrow size distribution centered at 0.88 nm, and using a method involving a redistribution of the Pt atoms using a high electron dosage in the STEM, it is shown that the clusters are present in two‐dimensional morphology. This conclusion is verified using intensity line scans. The in situ extended X‐ray absorption fine structure data are in good agreement with these observations. High‐resolution AC–TEM, which uses a broad coherent electron beam, and can thus offer advantages relative to STEM for structure determination of fine clusters, supported by image simulations of through‐focus series, were used to analyze the structures of Pt particles. The structures determined by using AC–TEM are consistent with STEM and EXAFS data in having a flat two‐dimensional morphology. Comparison of AC–STEM and AC TEM data for the same 700 °C reduced sample suggests that parallel‐beam TEM mode of imaging may be advantageous because of the less pronounced beam‐induced structural rearrangements that occur when imaging with a fine STEM probe.

In situ X‐ray Absorption Spectroscopy of Platinum Electrocatalysts

“…In both Figure 8 (a) and (b) the Pt−O peak can be observed to decrease, along with the XANES white‐line intensity, indicating the full reduction of Pt. At the same time the peaks corresponding to Pt−Pt increase in intensity, indicating the successful formation of Pt clusters [62] . EXAFS fitting at this point calculated a Pt−Pt CN of 6, indicating clusters of about 0.9 nm in size [63] .…”

“…At the same time the peaks corresponding to PtÀ Pt increase in intensity, indicating the successful formation of Pt clusters. [62] EXAFS fitting at this point calculated a PtÀ Pt CN of 6, indicating clusters of about 0.9 nm in size. [63] Finally, the samples underwent a second CO oxidation cycle, during which both samples showed the re-emergence of the PtÀ O peak alongside a lack of PtÀ Pt peaks.…”

Influence of Pt particle size and reaction phase on the photocatalytic performances of ultradispersed Pt/TiO2 catalysts for hydrogen evolution

“…S9). The instability of these pre-oxidized catalysts can be ascribed to photoreduction as well as to the reducing effect of hydrogen, which is known to destabilize metal cations initially anchored on oxides [38][39][40][41][42]. The 0.2Pt/P90 and 1Pt/90 fresh impregnates were also analyzed by STEM after the photocatalytic tests.…”

Multiscale Approach to the Dissociative Adsorption of Oxygen on a Highly Dispersed Platinum Supported on γ-Al2O3

“…[36][37][38][39] Gamma alumina is a versatile non-reducible support, often chosen at the industrial and laboratory scale for its high surface area and significant surface reactivity, 40 allowing for the dispersion of small metallic particles, if not Single Atom Catalysts. [41][42][43][44] Our aim is to get an atomic-scale insight in the surface structures described by the ultra-dispersed Pt/γ-Al 2 O 3 system in the presence of O 2 , and in the strength of the corresponding interaction.…”