The observations leading to these postulations were assembled
into a proposed deactivation mechanism model during steam
reforming of sulfur-containing liquid fuel on a noble metal promoted
Ni based catalyst, shown in Fig. 12. Four different stages
of catalyst micro-structure are shown, with relevance to catalyst
deactivation. At time t = 0, the catalyst is clean and active, free of any
carbon and sulfur. Shortly after the start of the reaction, the pure
catalyst was covered with hydrocarbon fragments along with some
concentration of sulfur-containing species. With further progress of
the reaction, Ni particles sintered, primarily due to Ostwald ripening.
Moreover, the Ni particles also become covered with sulfide
layers, thereby decreasing the reforming activity.