Hollow alumina spheres: fabrication, characterization, and their potential for operando magnetic resonance

Magnetic resonance (MR) techniques, including nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI), are powerful non-invasive tools for in situ and operando investigations of catalytic processes. However, their application to heterogeneous catalytic systems, particularly those involving gaseous reactants, is often limited by magnetic field inhomogeneities caused by conventional solid catalyst supports. In this work, we present hollow spheres as advanced porous catalyst supports that address this issue. Hollow alumina spheres were prepared via template synthesis and characterized using physicochemical methods, including XRD, BET, SEM and optical microscopy, confirming their η-Al₂O₃ phase, high surface area (~302 m²/g), and stable hollow geometry with thin walls (~0.05 mm). Unlike conventional bulk catalyst particles, these hollow alumina spheres do not cause significant distortions of magnetic field homogeneity. As a result, well-resolved ¹H NMR spectra and high-quality MR im-ages of gases and solutions in a granular bed were obtained, greatly enhancing precision in catalytic reactors characterization by MR techniques.