Abstract
Heterogeneous catalysis performed in the liquid phase is an important type of catalytic process which is rarely studied in situ. Using microfocus X-ray fluorescence and X-ray diffraction computed tomography (μ-XRF-CT, μ-XRD-CT) in combination with X-ray absorption near-edge spectroscopy (XANES), we have determined the active state of a Mo-promoted Pt/C catalyst (NanoSelect) for the liquid-phase hydrogenation of nitrobenzene under standard operating conditions. First, μ-XRF-CT and μ-XRD-CT reveal the active state of Pt catalyst to be reduced, noncrystalline, and evenly dispersed across the support surface. Second, imaging of the Pt and Mo distribution reveals they are highly stable on the support and not prone to leaching during the reaction. This study demonstrates the ability of chemical computed tomography to image the nature and spatial distribution of catalysts under reaction conditions.
Highlights
Heterogeneous catalysis performed in the liquid phase is an important type of catalytic process which is rarely studied in situ
This has given valuable new information about the atomic-nanoscale chemical structure coupled with information about the micro-distribution of such species, with applications across a wide range of disciplines such as materials, biomedical, environmental, and geophysical sciences.[2a,4] It is possible to observe how different preparation methods or deposition sequences affect the microdistribution of materials, and how structures respond to environmental changes, for example, changes in temperature, pressure, or gas treatments
The formation, phase, and spatial distribution of the active species can be mapped from catalyst preparation[3,5] right through to activation, operation,[2a,d] and eventually to deactivation, allowing for a better understanding regarding the correlation of structure and activity
Summary
Heterogeneous catalysis performed in the liquid phase is an important type of catalytic process which is rarely studied in situ. Using a combination of X-ray absorption nearedge spectroscopy (m-XANES), m-XRF-CT, and m-XRD-CT, we are able to determine what happens to the different Pt species, as well as to the Mo promoter, revealing the active state and stability of the catalyst through imaging a single catalyst particle.
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