Magnetic studies on dispersion effects in reduced nickel catalysts
A Faraday system and a dynamic hydrogen specific chemisorption system were developed for use in the Catalysis Research Laboratory. Silica supported nickel catalysts were prepared and appropriate reduction conditions determined to give superparamagnetic behavior of these catalysts. From the theory of superparamagnetism, the average and mean equivalent spherical diameters were calculated from data taken on the Faraday system. Techniques were developed to calculate the equivalent spherical diameter from the dynamic hydrogen specific chemisorption system. For all the catalysts, the diameters agree favorably. From the thermomagnetic studies in the paramagnetic region, it was verified that the Curie temperature and effective paramagnetic moment are functions of crystallite size and dispersion. Comparison of Curie data and perfect coordination models showed that the Curie points are functions of the average coordination number of a crystallite. The effective paramagnetic moment was determined to be a function only of dispersion. No model has yet satisfactorily explained this phenomena.