Cobalt-molybdenum-alumina catalysts

Exxon Donor Solvent Also known as EDS. A coal liquifaction process in which coal in solution in tetrahydronaphthalene is hydrogenated, using a cobalt/molybdenum/alumina catalyst. So-called because the hydrogen is donated by the tetrahydronaphthalene to the coal. Developed from the Pott-Broche process. Piloted by Exxon Research Engineering Company in the 1970s and operated at 250 ton/day in the Exxon refinery in Baytown, TX, from 1980 to 1982. 

Molybdenum oxide - alumina systems have been studied in detail (4-8). Several authors have pointed out that a molybdate surface layer is formed, due to an interaction between molybdenum oxide and the alumina support (9-11). Richardson (12) studied the structural form of cobalt in several oxidic cobalt-molybdenum-alumina catalysts. The presence of an active cobalt-molybdate complex was concluded from magnetic susceptibility measurements. Moreover cobalt aluminate and cobalt oxide were found. Only the active cobalt molybdate complex would contribute to the activity and be characterized by octahedrally coordinated cobalt. Lipsch and Schuit (10) studied a commercial oxidic hydrodesulfurization catalyst, containing 12 wt% M0O3 and 4 wt% CoO. They concluded that a cobalt aluminate phase was present and could not find indications for an active cobalt molybdate complex. Recent magnetic susceptibility studies of the same type of catalyst (13) confirmed the conclusion of Lipsch and Schuit. 

Reflection spectra for the MoNi-153 catalysts are shown in Figure 10. The 480°C calcined catalyst shows the characteristic absorption band (25) of octahedrally coordinated nickel ions. The 650°C calcined catalyst shows the characteristic spectrum of nickel aluminate. These reflection spectra indicate that the nickel ions migrate from the catalyst surface into the alumina, as has been observed also for the cobalt-molybdenum-alumina catalysts. 

For the high temperature calcined cobalt-molybdenum-alumina catalysts, the presence of a cobalt aluminate phase has been concluded from the reflection spectra. The BrtSnsted acid sites reappear in the spectrum of absorbed pyridine, indicating that the... 

The optimal activity for a cobalt-molybdenum-alumina catalyst is obtained by calcination at the higher temperatures. This means that the cobalt ions, present as a cobalt aluminate phase according to the reflectance spectra and the magnetic susceptibility measurements, still have a pronounced promoting action after this calcination. The assumption of cobalt present in the surface layer of the alumina lattice explains both the high activity due to the cobalt promotion as well as the presence of the second Lewis band. This configuration is shown schematically in Figure lib. 

An Investigation of the Activity of Cobalt-Molybdenum-Alumina Catalysts for Hydrodenitrogenation of Coal-Derived Oils... 

FeS also catalyzes the shift reaction, but its activity is only half that of Fe,04 [592]-[594], In principle the catalyst can tolerate up to 500 or 1000 ppm H2S, but with a considerable loss of mechanical strength, which is additionally affected by other contaminants in the gas, such as soot and traces of formic acid. For this reason the so-called dirty shift catalyst is used in this case, which was originally introduced by BASF [639]. This cobalt-molybdenum-alumina catalyst [603], [630], [640]-[644] is present under reaction conditions in sulfidized form and requires for its performance a sulfur content in the gas in excess of 1 g S/m3. Reaction temperatures are between 230 and 500 °C. COS is not hydrolyzed on dirty shift catalysts, but may be removed in the subsequent sour-gas removal stage using the Rectisol process. Separate hydrolysis on alumina based catalysts is possible at temperatures below 200 °C [603],... 

Figure 20. Change.s in the Mo 3d XPS spectrum from a cobalt-molybdenum-alumina catalyst during successive reduction treatments in hydrogen at SOOX 35 a) Air-fired catalyst b) Reduction time 15 min c) 50 min d) 60 min e) 120 min 0 200 min...

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