Sub-nanometer surface chemistry and orbital hybridization in lanthanum-doped ceria nano-catalysts revealed by 3D electron microscopy

Abstract

Surface chemical composition, electronic structure, and bonding characteristics determine catalytic activity but are not resolved for individual catalyst particles by conventional spectroscopy. In particular, the nano-scale three-dimensional distribution of aliovalent lanthanide dopants in ceria catalysts and their effect on the surface electronic structure remains unclear. Here, we reveal the surface segregation of dopant cations and oxygen vacancies and observe bonding changes in lanthanum-doped ceria catalyst particle aggregates with sub-nanometer precision using a new model-based spectroscopic tomography approach. These findings refine our understanding of the spatially varying electronic structure and bonding in ceria-based nanoparticle aggregates with aliovalent cation concentrations and identify new strategies for advancing high efficiency doped ceria nano-catalysts.

Efficient ammonia synthesis over a Ru/La0.5Ce0.5O1.75catalyst pre-reduced at high temperature

“…40 In addition, all of the EEL spectra showed Ce M 4,5 peaks ascribed to Ce 3+ and Ce 4+ at around 883.4 (as split peaks when the intensity was strong) and 901.8 eV and at 885.6 and 903.5 eV, respectively. 40 – 42 Ce 4+ predominated in the centre region (green square) of the thick catalyst particle, whereas Ce 3+ predominated at the edge (blue square) of the thick catalyst particle, and the proportion of Ce 3+ was highest at the centre (red square) of the thin catalyst particle. EELS maps of Ce in the thick and thin particles clearly showed the same tendency; that is, Ce 3+ was enriched near the surface of the catalyst particles ( Fig.…”

In situ oxidation and reduction of cerium dioxide nanoparticles studied by scanning transmission electron microscopy

“…As well as when addressing fundamental questions, such as, whether the lattice expansion inversely proportional to particle diameter observed in TEM measurements (Hailstone et al, 2009; Tsunekawa et al, 1999; Wu et al, 2004) is the result of the measurements being taken in a reducing environment (where lattice parameter dilates due phenomenon associated with reduction of Ce 4+ to Ce 3+ ) or others factors such as capillary pressure caused by surface stress (Diehm et al, 2012). Or how aliovalent dopants atoms spatially localize and influence the oxygen vacancy concentrations relative to bulk and surface (Collins et al, 2017). While the measurements here indicate that environment can influence the outcome of certain results, comprehensive measurements will be needed to address the aforementioned questions and quantitatively establish the spatial concentration of Ce 3+ atoms in particles as a function of atmosphere, potentially extracting thermodynamic information.…”

Nanomagnetic properties of the meteorite cloudy zone

“…First, the CS reconstruction volume was segmented to label voxels as either Ni-rich or Fe-rich. These chemical phase-specific subvolumes were then reprojected, using a discrete Radon transform in Sci-Kit Image (Python), giving a phase-specific thickness map at each tilt angle (40,41). These thickness maps were registered to the raw EDS spectra using image-processing routines in Matlab.…”