The preparation of tungsten based catalysts by impregnation of alumina pellets

Studies have been made of the impregnation process used to prepare catalysts suspended on pellets of γ-alumina. Attention has been focused on the impregnation of tungsten salts, alone or in combination with nickel or cobalt. The profile of the metals distribution within the pellet has been found to be very dependent on the conditions of impregnation. Impregnation was carried out from excess solution containing known concentrations of metal salt at controlled pH. The amount of tungsten deposited on the catalyst was found to be highest at pH > 6, while the amount of cobalt and nickel deposited increased as pH increased from 6 to 8 at which point bulk hydroxides precipitated on the pellet surface. The penetration of the metal salts into the pellet was found to be a function of pH, of concentration and of soak time, with clear evidence emerging that pore blockage was limiting penetration under some conditions. The results were explained in terms of the species present in solution under different conditions and their diffusion in the pore system versus adsorption on the pore wall. Conditions were established for the preparation of catalysts with metals concentrated near the pellet exterior or spread evenly throughout the pellet.