In situ characterization techniques:advances and challenges

Advanced characterization techniques are essential for gaining insights into the structural and chemical evolution of functional materials under reaction conditions [1]. In situ and operando methods have become increasingly important to overcome the limitations of traditional ex situ analysis conducted before and after reaction. However, there are many pitfalls one can encounter when conducting non-ambient experiments with elevated temperature, pressure, and humidity. This study highlights the necessity for interdisciplinary knowledge, such as surface and bulk chemistry, nano-size effects, fluid and gas dynamics, and flow-pressure relationships, to effectively plan and execute operando experiments through various application examples in heterogeneous catalysis. What remains non-trivial is the assessment and handling of the complexities associated with the use of corrosive or reductive/oxidative gas atmospheres.

This study presents the development of in-house operando X-ray powder diffraction (XRPD) and quasi-in situ X-ray photoelectron spectroscopy (XPS) setups for monitoring inorganic catalyst precursors under non-ambient conditions, including elevated temperatures, reaction gas environments, under pressure, or in a protective atmosphere. Operando XRPD enables real-time tracking of structural transformations, while quasi-in situ XPS provides surface-sensitive chemical state interpretation. Together, these techniques offer a comprehensive understanding of catalyst behavior under realistic reaction conditions and demonstrate the feasibility and value of in-house instrumentation for catalytic research.

[1] H. Petersen, C. Weidenthaler, A review of recent developments for the in situ/operando characterization of nanoporous materials, Inorg. Chem. Front., 9 (2022), 4244.