Coprecipitation kinetic effects

The optimum conditions for the precipitation may also vary when a batch procedure is adapted to work in a continuous mode. Thus the optimum pH range for the coprecipitation of lead with Fe(II )-HMDTC (pH 2-3) was found to be much narrower in the FI procedure than in the original batch procedure (pH 1-7) [21]. This was also considered to be a kinetic effect due to insufficient time for equilibrium in the continuous mode, so that coprecipitation can only be complete under the most favorable conditions. This phenomenon could, however, be made use of to overcome certain interferences from coexisting elements by kinetic discrimination, and should not be simply regarded as a drawback of the continuous approach. In manual batch procedures one always waits for a reaction to complete, unfortunately too often allowing interfering side reactions to fully develop. The equilibrium is therefore often achieved with a significant loss in selectivity. 

Separation and disposal of precipitate, coprecipitation, new contaminants added, decreased effectiveness with decreased concentration of target species, limited selectivity options Selectivity based on ion charge, new contaminants added, decreased selectivity with decreased concentration of target species, large space requirements, hydrophobic support, slow kinetics... 

The present work deals with sintering of Ni/AbOa catalysts under reducing and steamreforming reaction conditions. The effects of preparation method (impregnation and coprecipitation), lanthanum oxide promoter, oxide phases developed after calcination, sintering temperature and atmosphere were studied in terms of the time evolution of metal dispersion, size distribution properties and kinetic parameters obtained from a GPLE model. 

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