Description
The Strong Metal Support Interaction (SMSI) is a phenomenon observed in supported metal catalyst systems, in which reducible metal-oxide supports can form overlayers over the active metal nanoparticle (NPs) surface during reduction at elevated temperature in H2/N2 environment. X-ray standing wave (XSW) generated using periodic multilayer (ML) can be utilized to study surfaces and buried interface profiles with elemental selectivity at sub-nm scale. Under Bragg condition, standing wave field is formed inside and above the ML giving rise to nodes and anti-nodes. The strength of field intensity is suppressed and enhanced at nodes and anti-nodes respectively. By varying the angle of incidence, position of nodes and anti-nodes can be modulated allowing us to probe surfaces layers and interfaces locally. The stability of ML during the experiment is essential as any expansion or contraction of the bilayers period modifies the XSW and complicates that data analysis, specifically when the comparison of variously prepared samples is required.For example to study the SMSI effect it is necessary to compare metal-oxide-NPs layer before and after reduction, that requires high-temperature treatment.
In this work, thermally stable ML of MoNx/Si1-xNx of 20 periods was prepared to generate XSW and assess the applicability of XSW to study SMSI in Co/TiOx model catalyst system. The model catalyst system was synthesized on top of ML. By optimizing the ML structure and the TiOx layer thickness, we achieved maximum sensitivity for the changes in the Ti atomic distribution profile. The samples were reduced under H2/N2 environment at 600℃ for 1 hour and characterized by a combination of X-ray reflectivity and GIXRF. Partial or full encapsulation of Co NPs by a thin TiOx layer was identified by monitoring the changes in the phase of the Ti fluorescence signal before and after reduction. The changes in Ti distribution profile upon reduction will be presented.
| Period | 12 Oct 2023 |
|---|---|
| Held at | University of Hyogo, Japan |
| Degree of Recognition | International |