Sulfidation of nickel- and cobalt-promoted molybdenum–alumina catalysts using a radioisotope [formula omitted]-labeled H 2S pulse tracer method

Abstract

The sulfidation state in a series of nickel- and cobalt-promoted Mo/Al 2O 3 catalysts was investigated using 35 S radioisotope pulse tracer methods (RPTM). Several pulses of 35 S -labeled H 2S ([ 35 S ]H 2S) 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 [ 35 S ]H 2S 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, Co 9S 8 and MoS 2, was attained at 400°C for all catalysts. Moreover, it was suggested that only molybdenum was sulfided below 300°C; the sulfidation of nickel oxide and cobalt oxide in the Ni– or the Co–Mo/Al 2O 3 catalyst is more difficult at lower temperatures and the sulfidation of nickel and cobalt species occurs only at higher temperatures (above 300°C).