Structural transitions during Ni nanoparticle formation by decomposition of a Ni-containing metal–organic framework using in situ total scattering

Abstract

For improved and rational design of catalysts, in-depth knowledge of their formation and structural evolution during synthesis is a key parameter. Thus, the preparation of a Ni methanation catalyst derived from a Ni-containing metal–organic framework Ni(BDC)(PNO) under different gas atmospheres (He vs. 10% H₂/He) and temperature (342 °C, 375 °C, 411 °C, and 500 °C) conditions was studied thoroughly using in situ pair distribution function analysis, X-ray absorption spectroscopy and thermogravimetric analysis. Framework decomposition is initiated by a distortion of the metal–organic framework (MOF) structure, followed by the release of trapped solvent molecules. Then, the pyridine-N-oxide (PNO) linker is released from the framework, followed by the benzenedicarboxylate (BDC) linker, leading to the collapse of the framework and the formation of 2 nm nickel nanoparticles surrounded by a carbon shell, that grow to 4 nm upon further heating. Without a reducing atmosphere, carbon is intercalated into the Ni structure forming a Ni_hcp side phase, which is inactive in the methanation reaction.