Mitigating charging in NAP-XPS: a practical approach for insulating catalyst powders

• Common NAP-XPS methods show severe charging and differential charging issues. • A new aluminium disk mounting method effectively eliminates differential charging. • No electron flood gun needed for stable NAP-XPS of insulating catalyst supports. • Reliable method for high-temp NAP-XPS of supported catalysts in reactive environment. • Suitable for high x-ray flux at synchrotron sources. X-ray photoelectron spectroscopy (XPS) is a major technique in catalyst research due to its ability to determine chemical states on the surface. Near ambient pressure XPS (NAP-XPS) enables in situ analysis, offering valuable insight into catalytic processes. However, modern catalysts are often supported on non-conductive supports such as TiO 2 or SiO 2 , which can present significant challenges for XPS analysis due to charging and differential charging. These issues can distort spectral data, rendering data unusable and wasting valuable instrument time. While several sample preparation strategies exist, many are limited by not allowing high temperature analysis, the risk of sample loss (e.g., from powder flaking off), or continued susceptibility to charging. In this work, we introduce a simple, robust, and time-efficient method for mounting catalyst powders by compressing them between aluminium foil disks. This approach provides excellent sample hold, minimises charging effects, and is suitable for high-temperature NAP-XPS analysis and synchrotron x-ray sources. The method addresses key limitations of conventional preparation techniques and enables more reliable characterisation of insulating catalyst materials.