Focused Ion Beam (FIB) Milling and Automotive Catalysis Aging: A Novel Approach for the Direct Observation of Interfacial and Sub-Surface Chemical and Structural Properties Relevant to Catalyst Aging and Functionality

摘要

The combined focused ion beam/scanning electron microscopy/energy dispersive X-ray spectroscopy (FIB/SEM/EDX) system is a novel tool for the automotive catalysis field. Automotive emissions such as SO_x, NO_x, and particulate matter (PM) are regulated to various extents throughout the world, requiring the use of multiple aftertreatment components such as the diesel particulate filter (DPF), diesel oxidation catalyst (DOC), three-way catalytic converter (TWC), Lean NO_x trap (LNT) and selective catalytic reduction (SCR). While these aforementioned aftertreatment components are generally multifunctional and robust in design, thermal and chemical aging over the components' useful lifetimes results in significantly degraded performance leading to increased engine emissions levels and decreased fuel economy. While the component sizes themselves are generally large (10s of cm to ≈1/2 m), component aging mechanisms usually dominate on the nm-μm scales. In particular, this study has used the FIB/SEM/EDX system to investigate the aging of the diesel particulate filter (DPF) due to engine lubricant-derived inorganic ash accumulation. The FIB/SEM/EDX system has been used in the automotive aftertreatment field for the first time with many surprising and significant findings. Although the samples used in this study are quite different to those typically found in FIB studies, the authors have shown that the FIB/SEM/EDX system is a valuable tool in this research area, especially for the investigation of μm-size intra-particle structure and nm-μm interfacial/sub-surface details around the aged catalyst surface.