Sulfidation of nickel- and cobalt-promoted molybdenum-alumina catalysts using a radioisotope 35S-labeled H2S pulse tracer method

The sulfidation state in a series of nickel- and cobalt-promoted Mo/Al2O3 catalysts was investigated using S-35 radioisotope pulse tracer methods (RPTM). Several pulses of S-35-labeled H2S ([S-35]H2S) were introduced into catalysts in a nitrogen stream until the radioactivity in the recovered pulse approached the radioactivity of the introduced pulse. From the amount of [S-35]H2S introduced, the amount of sulfur accumulated on the catalyst was estimated. The amounts of sulfur accumulated on the catalysts increased with increasing temperature for all catalysts and the cobalt-promoted catalysts showed features similar to those of the nickel-promoted catalysts. It was found that the sulfided states of the catalysts close to the stoichiometric states, where Ni, Co and Mo are present as NiS, Co9S8 and MoS2, was attained at 400 degrees C for all catalysts. Moreover, it was suggested that only molybdenum was sulfided below 300 degrees C; the sulfidation of nickel oxide and cobalt oxide in the Ni- or the Co-Mo/Al2O3 catalyst is more difficult at lower temperatures and the sulfidation of nickel and cobalt species occurs only at higher temperatures (above 300 degrees C). (C) 2000 Elsevier Science B.V. All rights reserved.