PREPARATION VARIABLES IN NICKEL CATALYSTS

Nickel-on-silica catalysts were prepared by the homogeneous precipitation of slowly decomposing urea. After reduction the crystallite size distribution (CSD) of the nickel was determined from magnetic measurements. This technique was found to give very narrow CSDs and is much more reproducible than conventional impregnation methods. The nickel loading may be controlled by the solution concentrations and time of precipitation but higher values lead to broader distributions. The amount of reduced nickel is a function of the hydrogen flow rate and time, but these factors do not influence the CSD. Increasing reduction temperatures produce broader CSDs. Calcination has no effect on the resulting CSDs, nor does passivation in air after reduction. The uniform and stable crystallites resulting from this method are a consequence of the precipitation of nickel hydrosilicate homogeneously over the silica surface. This compound reduces slowly so that the metal does not sinter during reduction and small, uniform crystallites are produced. © 1978.