Research ArticleAPPLIED PHYSICS

Sparse ab initio x-ray transmission spectrotomography for nanoscopic compositional analysis of functional materials

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Science Advances  09 Jun 2021:
Vol. 7, no. 24, eabf6971
DOI: 10.1126/sciadv.abf6971
  • Fig. 1 Illustration of sparse XTNES acquisition.

    (A) Examined VPO catalyst pellet as retrieved from the reactor (top left). Preshaped sample mounted on a tomography pin (top right, black arrow) and focused ion beam milled sample cylinder (bottom). Scale bars are 5 mm, 1 mm and 10 μm. The white circle indicates the region from which the sample cylinder was extracted. The blue rectangle indicates roughly the field of view during XTNES tomogram acquisition. Photo credit: Zirui Gao, PSI, ETHZ. (B) Spectral tomograms were assembled by acquiring a series of angularly sparse ptychographic tomograms across the vanadium K-edge. (C) Graphical illustration of the acquisition scheme of tomography angular orientations versus x-ray photon energy. For each energy, the Crowther criterion is indicated by small dots, while larger dots indicate angularly sparse measured projections. At each energy, an offset to the angle based on a golden ratio is added to each projection to maximize the available information diversity.

  • Fig. 2 Local vanadium K-edge spectra and XTNES tomograms of industrial VPO catalysts.

    (A) Example of two voxel-level phase and KKT-obtained absorption spectra. From these spectra, we obtain quantitative values for (i) the electron density, (ii) vanadium concentration, (iii) vanadium oxidation state, and (iv) pre-peak intensity. (B) Hue saturation value 3D color map used for the combined visualization of electron density, vanadium concentration, and vanadium oxidation state. (C) 3D volume rendering of the pristine catalyst based on the color map presented in (B) and axial virtual slices taken from the middle of the catalyst sample highlighting the individual quantities. (D) 3D volume rendering and virtual slices of the used catalyst based on the color map in (B). Scale bars, 2 μm. The positions of the voxels discussed in (A) are marked in (C) using a cross and a circle, respectively.

  • Fig. 3 Microstructural analysis, local structure optimization, and defect Identification in vanadium phosphorus oxide catalysts.

    (A) Pre-peak intensity volume renderings, shown as (iv) in Fig. 2A, of the pristine and used VPO catalyst. (B) Volume rendering of the pre-peak intensity of a single vanadyl pyrophosphate [(VO)2P2O7] grain found in the used VPO catalyst. Changes in pre-peak intensity are displayed in the form of a gradient color map ranging from blue to green. Scale bars, 2 μm. (C) 3D distance maps of XTNES extracted quantities—(i), (ii), and (iii)—from the pore space into the used VPO catalyst. Magnitudes encountered within the first 80 nm of the material are shown in gray, which were used as boundary conditions for ground-state total energy calculations of the crystal structure of vanadyl pyrophosphate in contact with the reactive medium, thereby found to be vanadyl deficient (VO). The gray dotted lines show reference values of both the ideal and defective structure. (D) Ideal crystal structure of vanadyl pyrophosphate including {200} and {024} surface projections as well as vanadyl defective projections of the calculated catalyst structure in contact with the reactive medium (gray box).

Supplementary Materials

  • Supplementary Materials

    Sparse ab initio x-ray transmission spectrotomography for nanoscopic compositional analysis of functional materials

    Zirui Gao, Michal Odstrcil, Sebastian Böcklein, Dennis Palagin, Mirko Holler, Dario Ferreira Sanchez, Frank Krumeich, Andreas Menzel, Marco Stampanoni, Gerhard Mestl, Jeroen Anton van Bokhoven, Manuel Guizar-Sicairos, Johannes Ihli

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    The PDF file includes:

    • Extended Materials and Methods
    • Selective oxidation of n-butane to MA within an industrial setting
    • Suggested active sites in VPO catalysts
    • Ptychographic computed x-ray tomography and sensitivity to variations in incident energy
    • Local structure optimization
    • Figs. S1 to S15
    • Tables S1 and S2
    • Legends for movies S1 and S2
    • References

    Other Supplementary Material for this manuscript includes the following:

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