Operando X-ray absorption spectroscopy on Nickel-loaded zeolites

The aim of this work was to investigate the local structure and chemical state of nickel after its incorporation into the zeolite ZSM-5, with the objective being the understanding of the role of the different synthesis routes on Ni dispersion and reducibility. Two Ni/ZSM-5 catalysts were prepared by the Catalysis and Spectrochemistry Laboratory (LCS, Caen) using distinct synthesis methods: conventional wetness impregnation and co-precipitation. To probe the structural and electronic environment of Ni species, operando Ni K-edge X-ray Absorption Spectroscopy (XAS) was carried out at the BM23 beamline of the European Synchrotron Radiation Facility (ESRF) during H₂ temperature-programmed reduction (TPR). The data were analyzed using Principal Component Analysis (PCA), SIMPLISMA, and Multivariate Curve Resolution–Alternating Least Squares (MCR-ALS) to identify and as well as quantify the evolving Ni species throughout the reduction process. Three distinct components were resolved in both catalysts: a metallic Ni phase, a nanostructured NiO phase, and a Ni²⁺ phyllosilicate-like phase associated with the zeolite framework. Subsequent fitting of the EXAFS spectra collected during cooling confirmed the formation of metallic Ni nanoparticles with an average coordination number of 10.7. These results demonstrate that the co-precipitation method leads to the formation of a more stable and framework-incorporated Ni environment compared to conventional impregnation, providing insights towards the optimization of Ni-based zeolitic catalysts for applications such as plastic pyrolysis.