CHARACTERIZATION OF THE STANDARD NICKEL SILICA CATALYST EURONI-1 .3. INVESTIGATIONS OF CATALYST STRUCTURE

In two earlier papers the organisational aspects of the collaborative project and the chemistry of catalyst precipitation and reduction were presented, as well as the chemical composition of the EuroNi-1 catalyst. In the present paper the results obtained by means of X-ray diffraction, electron spectroscopy, visual and electron microscopy and with magnetic measurements are presented. From these data a detailed structural image of the catalyst is evolved. Information on nickel dispersion in the catalyst reduced at 450 and 650-degrees-C is obtained. Surface area measurements from nitrogen adsorption isotherms were carried out on the unreduced catalyst as well as on the catalyst reduced under different conditions. Agreement between laboratories was reasonable. On different reduced states the nickel surface area was determined by means of hydrogen adsorption at ambient temperature. Very different ideas on monolayer definition are present within the group. Differences in reduction procedure further contribute to divergence in nickel surface areas obtained. The author makes a choice based on a number of experimental observations. From the chosen surface area data for catalysts reduced at about 450 and 650-degrees-C average nickel crystallite sizes are calculated, with two assumptions for the shape of the nickel crystallites, hemisphere and sphere. The crystallite sizes thus obtained are compared with data obtained by means of the physical techniques mentioned above. For low temperature reduction the hemisphere model is the more successful, for the higher temperature the full sphere gives better correlation.