We report the characterization of two catalysts containing (I) 44 and (II) 57.3 wt. percent of Ni dispersed on Al2O3, containing a graphite binder. It is shown that magnetization (&sgr;) versus H/T curves provide not only an analysis of very small (<100 A˚) catalytically active particles, but also provide clues to the changes in particle profiles (size and shape) during the sintering of Ni dispersions. The conglomeration of the superparamagnetic (single‐domain isotropic) particles to ’’needle’’ shaped (single‐domain anisotropic) particles is analyzed in terms of the corresponding changes in the coercive force. Catalyst (I) with its lower nickel loading was found to be more thermally resistant to the formation of the multidomain particles over the entire HTT range. Work in progress on correlating the electronic parameters of Ni with its catalytic activity is outlined.