Temperature Programmed Sulfiding of CoO/MoO₃/γ‐Al₂O₃ Catalysts

Abstract

Abstract The sulfiding of CoO/MoO 3 /γ‐Al 2 O 3 catalysts was studied by a technique called Temperature Programmed Sulfiding (TPS). Cobalt loading, calcination temperature and pretreatment were varied. CoO/MoO 3 /γ‐Al 2 O 3 catalysts sulfide at lower temperatures than model compounds such as CoO, MoO 3 and CoMoO 4 because of the higher dispersion in the catalysts. Sulfiding of Mo in CoO/MoO 3 /γ‐Al 2 O 3 catalysts is dominated by O‐S exchange, reduction of Mo is due to Mo‐S bond rupture followed by reduction of elemental sulfur, in the same way as occurs in MoO 3 /γ‐Al 2 O 3 catalysts. For Co in CoO/MoO 3 /γ‐Al 2 O 3 catalysts the sulfiding pattern depends strongly on the calcination temperature: low calcination temperatures (785 K) lead to catalysts which show sulfiding of Co species in the same temperature range as Mo, and an increase in the reduction rate of elemental sulfur formed by reduction of Mo oxysulfides. Sulfiding of CoO/MoO 3 /γ‐Al 2 O 3 leads to Co species which are stabilized and more disperse than those in sulfided CoO/MoO/γ‐Al 2 O 3 catalysts. Calcination temperatures higher than 785 K cause a decrease of the amount of easily sulfidable Co species, and an increase in the amount of Co which sulfides at high temperature (1000 K). As was found for MoO 3 /γ‐Al 2 O 3 and CoO/γ‐Al 2 O 3 catalysts the “water content” of CoO/MoO/γ‐Al 2 O 3 catalysts has an influence on the sulfiding patterns: “wet” catalysts (containing up to 6% water) with low Co loading sulfide at lower temperature than dried catalysts. Sulfiding (in TPS) proceeds at a higher rate than reduction by H 2 (in TPR).