Operando laboratory XAS of Ni nanoparticles in CO2 methanation using a plug-flow fixed-bed cell with von Hámos spectrometer

Abstract

A plug-flow fixed-bed cell for operando laboratory X-ray absorption spectroscopy (XAS) using a von Hámos spectrometer is presented for heterogeneous catalysis studies. The cell operates up to 1000 °C and 10 bar with controlled gas atmospheres provided by three mass flow controllers and rapid infrared heating. The performance of the setup is demonstrated across a broad usable energy range of the spectrometer, and as a proof of principle, operando Ni K-edge XAS was used to monitor the activation of a 20 wt% NiO/COK-12 catalyst under CO₂ methanation conditions (CO₂ : H₂ = 1 : 4, 350 °C). Time-resolved spectra acquired on a 5 min timescale reveal the reduction of NiO nanoparticles to metallic Ni during activation, directly correlating with increasing catalytic activity quantified by online gas chromatography. This setup enables minute-scale, time-resolved structural analysis of working catalysts under industrially relevant conditions, providing a practical laboratory-based alternative complementary to synchrotron studies.