Sulfidation state of alumina-supported molybdenum catalysts estimated by a 35Sradioisotope tracer method
Abstract
The sulfidation state in Mo/Al2O3 and Co-Mo/Al2O3 catalysts have been investigated using a 35S pulse tracer method. [35S]H2S pulses were introduced into Mo/Al2O3 or Co-Mo/Al2O3 in a nitrogen stream until the amount of radioactivity in one pulse was constant, i.e. the catalyst no longer reacted with [35S]H2S. From the amount of reacted [35S]H2S, the amount of sulfur accumulated on the catalyst was estimated. The amounts of sulfur accumulated on the Mo/Al2O3 and Co-Mo/Al2O3 catalysts increased with increasing temperature. The amounts of sulfur accumulated on Mo/Al2O3 with 12 wt.% MoO3 at 100, 200, 300 and 400°C were 34.0, 38.5, 50.7 and 60.5 mg S (g cat)-1, respectively and the value at 400°C corresponded to a sulfidation state of MoS2.2/Al2O3. At the same temperature, the amount of sulfur accumulated on Mo/Al2O3 increased with increasing the amount of molybdenum loaded. Below 300°C, the amount of sulfur accumulated on Mo/Al2O3 was almost same as that on CoMo/Al2O3. The amount of sulfur accumulated on CoMo/Al2O3 (CoO: 3.8 wt.%, MoO3: 12.3 wt.%) at 400°C was 73.4 mgS (g cat)-1, larger than that on Mo/Al2O3 with 12 wt.% MoO3. These results suggest that only molybdenum is sulfided in both Mo/Al2O3 and CoMo/Al2O3 catalysts below 300°C and that only at 400°C is cobalt on CoMo/Al2O3 sulfided.