We use a nickel catalyst in our Thermal Dynamix ammonia dissociators while our endothermic and rich exothermic generators are charged with 3/4" cube type nickel catalyst. The spherical catalyst looks very much like charcoal grey marbles.
The 1/2" spherical configuration provides a high packing density in the dissociator retort which allows us a great deal of confidence in our claim of specific capacity of any given unit size, while not packing so tightly as to present a plugging problem. The cube type catalyst provides the endo and exo generators a significantly less dense composition which allows operation at very rich mixtures while minimizing plugging and enabling the use of periodic burn-off procedures to clear the catalyst of surface deposits of carbon.
We believe the use of nickel, as opposed to iron, provides additional catalyst life and durability.
And while we're on the subject: We like to see our dissociators fed metalurgical grade ammonia.
It's clean, has no water in it and contains no sulfur. In our recommended specifications for ammonia
feedstock we warn against the presence of sulfur; the reason being that sulfur is attacks the catalyst
and destroys its ability to promote the dissociation of the ammonia vapor.
Having said all this, every once and a while we've discovered a customer's use of industrial ammonia
feedstock and in one case, agricultural grade ammonia. This stuff is, by any reasonable standard, of
a quality below that for which any dissociator is designed. It contains contaminates such as oil and
water, mercaptans and even occasional sulfur, at levels above our recommendations and the use
of it is ardently courting heartbreak and disaster.