Synthesis of a magnetically heatable ceria–supported ruthenium catalyst via deposition of nanocrystalline ceria on silica-coated magnetic iron–oxide nanoparticles

ABSTRACT We report the synthesis of a ceria-based catalyst support containing embedded magnetic iron–oxide nanoparticles (IONPs) that enable heating under a high-frequency alternating magnetic field. The ≈11 nm IONPs, synthesized by co-precipitation of Fe 2+ /Fe 3+ ions at room temperature, were coarsened to ≈18 nm through subsequent hydrothermal treatment at 120 °C and then coated with a ≈2 nm silica layer. The catalyst support was prepared by depositing nanocrystalline ceria (CeO 2 ) onto the IONPs via controlled precipitation of Ce 3+ ions in the presence of hexamethylenetetramine (HMTA) in aqueous suspension. When deposited directly on the iron oxide, ceria formed small agglomerates of ≈10 nm octahedral nanocrystallites, whereas deposition on silica-coated IONPs produced a homogeneous 3–6 nm-thick shell composed of ≈3 nm globular crystallites. Special attention was given to elucidating the mechanism of shell formation. The magnetic catalyst was obtained by precipitating Ru nanoparticles (1–2 nm) onto the ceria support. Morpho-structural characterization was performed by XRD, TEM, and aberration-corrected STEM. Static and dynamic magnetization measurements at room temperature were used to assess the magnetic and heating performance. At low field amplitudes (<15 mT), catalysts prepared with IONPs of both sizes exhibited similar specific absorption rates, whereas at higher amplitudes the larger IONPs demonstrated superior heating efficiency. The catalytic performance was demonstrated in the magnetically heated hydrogenation of the bio-based compound 5-(hydroxymethyl)furfural to 2,5-bis(hydroxymethyl)furan, showing high activity, 100% selectivity, and excellent stability upon recycling.