Magnetic anisotropy and granulometry of Ni/CeO2 catalyst

Abstract

Ni supported on CeO₂ are catalysts used for hydrogenation reactions. In this work, magnetic properties of two samples reduced at 250 and 400 °C in hydrogen are reported, with small nickel concentrations (6 vol %) so that magnetic interactions between nickel particles are negligible. Below 500 K, a progressive spin freezing of nickel particles is evidenced by the observation of a remanent magnetization and a deviation of the magnetic susceptibility from the Curie Weiss law. A model beyond the superparamagnetic approximation from which we derive the size distribution f(d) of the nickel particles is presented. It is found that the two samples differ by the particle size heterogeneity, although the mean size d is about the same (7–8 nm). It is shown that the blocking of the Ni particles is due to a strong strain anisotropy (3×10⁶ erg cm⁻³), and conclude that the difference in the catalytic activity between the two samples is due to a strong interaction with the support, rather than a difference in the particle‐size distribution.