X‐ray photoelectron spectroscopic and electron spin resonance studies of cobalt species in CoMo/γ‐Al 2 O 3 hydrodesulfurization catalysts after operation for eight hours under pressure

We report X‐ray photoelectron spectroscopic and electron spin resonance data on Co/γ‐Al 2 O 3 and CoMo/γ‐Al 2 O 3 catalysts Co/(Co+Mo) = 0.35 after sulfidation and catalytic operation under 30 bars pressure at 305°C for eight hours. The catalysts were protected from air contamination. Data on catalytic activity (hydrogenolysis of thiophene and hydrogenation of cyclohexene), X‐ray diffraction and diffuse reflectance spectroscopy are also reported. A reduced cobalt species is associated with Co 9 S 8 on Co/γ‐Al 2 O 3 . This species is not detected on CoMo/γ‐Al 2 O 3 , where cobalt occurs as CoAl 2 O 4 and as cobalt in a fully sulfided form, quite probably as Co 9 S 8 . If the hypothesis of the synergy by contact is correct, the results indicate that unreduced Co 9 S 8 is the activating agent.