The formation of aromatic/polymeric carbon was seen to be
effected by the presence of sulfur in the feed and by the Rh content
of the catalyst. As the Ni surface becomes saturated with sulfur, Ni
becomes less effective in catalyzing the conversion of the hydrocarbon
into hydrogen and carbon oxides. Rather, hydrocarbons
adsorbed onto sulfur poisoned Ni sites migrate to the surrounding
alumina support, where they undergo acid cracking to produce
cracked products. The cracked products may then undergo dehydrogenation
to give unsaturated hydrocarbons on the support, or
through catalytic interaction with Rh may produce hydrogen and
carbon oxides.