No 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.

The elemental preparation steps of impregnation and drying of Ni/γ-Al 2 O 3 catalyst bodies have been studied by combining UV-vis and IR microspectroscopy. The influence of the number of chelating ligands in [Ni(en) 2+ precursor complexes (with en ) ethylenediamine and x ) 0-3) has been investigated. UV-vis measurements after impregnation showed that, regardless of the en:Ni 2+ ratio in the precursor solution, Ni 2+ was already detected in the core of the pellets 5 min after impregnation. The alumina support did bring about, however, gradients in the nature of the Ni 2+ species upon first contact with the lowest en:Ni 2+ ratio solutions, but these gradients disappeared after 30-60 min of impregnation. After 60 min, UV-vis seemed to indicate Ni-O-Al interactions between Ni 2+ and the support, when water was initially part of the first coordination sphere of Ni 2+ , which was supported with the results obtained after drying. For dried samples, UV-vis showed a gradient of [Ni(en) x (H 2 O) 6-2x ] 2+ inside the pellets, with an en-poor region in the core and an en-rich region in the edges of the catalyst bodies, when [Ni(en) were the starting complexes. IR microspectroscopy confirmed these en radial profiles, while EDX measurements showed that an Ni 2+ egg-shell distribution goes hand-in-hand with an egg-shell distribution of en. The number of en ligands determined the interactions of Ni 2+ with the support after impregnation and controlled the redistribution of metal-ion species during drying. Moreover, when redistribution of Ni 2+ occurred during drying, its transport toward the outer rim of the extrudates came about together with changes of the local en:Ni 2+ ratio.