Molybdenum magnetic susceptibility

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. 

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. 

Molybdenum is paramagnetic. Numerous determinations of the magnetic susceptibility have been made, but the results obtained are widely divergent. When obtained in the form of a powder it is grey in colour and lustreless, though the strongly compressed powder exhibits metallic lustre. The metal melts at 2450 30° C., and may, though with difficulty, be distilled in the electric furnace. ... 

Several tris-(P-diketonato)molybdenum(iii) complexes, ML3 (L = acac, tfac, hfac, dbm, or btfac), have been prepared by thermal or photolytic oxidative decarbonylation of Mo(CO)g with HL and purified by repeated fractional sublimation. The i.r. and electronic spectra of these compounds have been obtained and their magnetic susceptibilities show Curie-law behaviour, with... 

Fig. 7.3. Internally pressured cell for magnetic susceptibility measurements of fluid selenium by the Faraday method (Freyland and Cutler, 1980). The sealed quartz capsule containing the sample is mechanically supported by the surrounding molybdenum pressure cell.

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