Tomographic Energy Dispersive Diffraction Imaging To Study the Genesis of Ni Nanoparticles in 3D within γ-Al₂O₃ Catalyst Bodies

Abstract

Tomographic energy dispersive diffraction imaging (TEDDI) is a recently developed synchrotron-based characterization technique used to obtain spatially resolved X-ray diffraction and fluorescence information in a noninvasive manner. With the use of a synchrotron beam, three-dimensional (3D) information can be conveniently obtained on the elemental composition and related crystalline phases of the interior of a material. In this work, we show for the first time its application to characterize the structure of a heterogeneous catalyst body in situ during thermal treatment. Ni/gamma-Al(2)O(3) hydrogenation catalyst bodies have been chosen as the system of study. As a first example, the heat treatment in N(2) of a [Ni(en)(3)](NO(3))(2)/gamma-Al(2)O(3) catalyst body has been studied. In this case, the crystalline [Ni(en)(3)](NO(3))(2) precursor was detected in an egg-shell distribution, and its decomposition to form metallic Ni crystallites of around 5 nm was imaged. In the second example, the heat treatment in N(2) of a [Ni(en)(H(2)O)(4)]Cl(2)/gamma-Al(2)O(3) catalyst body was followed. The initial [Ni(en)(H(2)O)(4)]Cl(2) precursor was uniformly distributed within the catalyst body as an amorphous material and was decomposed to form metallic Ni crystallites of around 30 nm with a uniform distribution. TEDDI also revealed that the decomposition of [Ni(en)(H(2)O)(4)]Cl(2) takes place via two intermediate crystalline structures. The first one, which appears at around 180 degrees C, is related to the restructuring of the Ni precursor on the alumina surface; the second one, assigned to the formation of a limited amount of Ni(3)C, is observed at 290 degrees C.

Infrared and Raman imaging of heterogeneous catalysts

“…Bert Weckhuysen (42), a native Belgian, received his master degree from Leuven University (Belgium) in 1991. After finishing his PhD studies under the supervision of Prof. Schoonheydt in 1995, he has worked as a postdoctoral fellow with Prof. Wachs at Lehigh University (USA) and with Prof. Lunsford atintroduced in the field of heterogeneous catalysis.…”

In‐situ Scanning Transmission X‐Ray Microscopy of Catalytic Solids and Related Nanomaterials

“…Beautiful space and time resolved hard X-ray experiments have been performed by Grunwaldt et al [48] Alternative micron range hard X-ray experiments involve the so-called TEDDI technique. [49,50] Figure 5. The range of experimental, spatial resolutions (pink) and maximal sample thicknesses (blue) are indicated on a logarithmic scale for, from bottom to top, STEM-EELS, STXM at 300 eV, STXM at 1.5 keV and STXM at 10 keV.…”

Dynamic X‐Ray Diffraction Computed Tomography Reveals Real‐Time Insight into Catalyst Active Phase Evolution

“…respectively. Previously, due to a combination of a lack of sufficient data quality and kinetic resolution, it was not possible to 1) determine the nature of the first Ni-containing crystalline phase, 2) observe in such detail this stepwise decomposition leading to the formation of a number of intermediate species, and finally 3) to differentiate the presence of hcp Ni from Ni 3 C. [16,30] Distinguishing between Ni 3 C and hcp Ni is now possible from the data since reliable peak intensities can be extracted; the relative intensity of the reflection at 6.168 2q is more consistent with the presence of hcp Ni than Ni 3 C.…”