Here we present a magnetically recoverable palladium catalyst prepared by immobilization of palladium over silica-coated magnetite nanoparticles. The catalyst reduced by molecular hydrogen contains palladium nanoparticles well distributed and stabilized in the magnetizable support surfaces and converts cyclohexene to cyclohexane under mild reaction conditions (75 °C and 6 atm) with TOF of 11 500 h⁻¹. The catalyst was easily recovered with a permanent magnet in the reactor wall and reused for up to 20 recycles of 2500 TON each without any significant loss in catalytic activity, demonstrating an efficient recycling process for hydrogenation reactions.

Six-line ferrihydrite(FH) nanoparticles have been synthesized in the core of reverse micelles, used as nanoreactors to obtain average particle sizes $$ $\approx$ 2 to 4 nm. The blocking temperatures $T_B^m$ extracted from magnetization data increased from $\approx 10$ to 20 K for increasing particle size. Low-temperature \MOS measurements allowed to observe the onset of differentiated contributions from particle core and surface as the particle size increases. The magnetic properties measured in the liquid state of the original emulsion showed that the \FH phase is not present in the liquid precursor, but precipitates in the micelle cores after the free water is freeze-dried. Systematic susceptibility $\chi_{ac}(\emph{f},T)$ measurements showed the dependence of the effective magnetic anisotropy energies $E_{a}$ with particle volume, and yielded an effective anisotropy value of $K_{eff} = 312\pm10$ kJ/m$^3$.