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

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