n-Heptane hydrocracking over a sulfided NiMo/Y zeolite catalyst: reversible deactivation of the zeolite by sulfur - containing molecules

Abstract Hydrocracking of n-heptane was carried out over a sulfided NiMo/Y zeolite catalyst in the presence of ammonia and hydrogen sulfide. An increase in the hydrogen sulfide pressure decreased the activity of the catalyst and increased the isomerization/cracking ratio, which indicated a poisoning of the acid sites. This poisoning was accompanied by an increase in the formation of coke on the catalyst when the hydrogen sulfide pressure increased. The coke was composed mainly of sulfur-containing molecules, namely dimethyl polysulfides (tri-, tetra- and pentasulfides), and also pure sulfur: S 8 . The deactivation of the catalyst was due to a blockage of the porosity of the zeolite by the sulfur polymers because of the low volatility of these compounds. The higher the hydrogen sulfide pressure the greater the amount of sulfur polymers, this phenomenon being totally reversible.