Sulfidation state of alumina-supported molybdenum catalysts estimated by a S-35 radioisotope tracer method

The sulfidation state in Mo/Al2O3 and Co-Mo/Al2O3 catalysts have been investigated using a S-35 pulse tracer method. [S-35]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 [S-35]H2S. From the amount of reacted [S-35]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.% MoO33 at 100, 200, 300 and 400 degrees C were 34.0, 38.5, 50.7 and 60.5 mg S (g cat)(-1), respectively and the value at 400 degrees 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 degrees 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 degrees C was 73.4 mg S (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 degrees C and that only at 400 degrees C is cobalt on CoMo/Al2O3 sulfided.