Crystallite size distributions of sintered nickel catalysts

Abstract

Sintering of nickel on silica was followed by measuring the crystallite size distribution with a magnetic granulometry method. The initial distribution of a sample prepared by slow, homogeneous precipitation-deposition was very narrow but could be broadened by thermal treatment. The effects of temperature, time, initial distribution, and nickel concentration were studied. The dispersion was very stable at 673 K but showed some broadening for sintering times up to 100 hr. Above 723 K, however, sintering occurred with the disappearance of small crystallites, reaching a limiting log-normal shape, independent of initial distribution or nickel concentration below 17 wt%. These results were interpreted as particle migration. The decline of surface area showed an order of 10 and an activation energy of 200 kJ/mole. At temperatures approaching 873 K, the resulting distributions were bimodal, suggesting that the influence of pore-size distributions should be considered in sintering models.