Reactivity studies, transition metal molybdenum

Studies performed in previous years (ref.3-5) over molybdenum loaded zeolites in HDS reaction showed that reactivity of these catalysts depends on the type of zeolite used, concentration of transition metal and the way of preparation. However, preparation of molybdenum based catalysts applying ammonium heptamolybdate usually results in low dispersion of molybdenum sulfides and relatively low activity. Recent studies showed that saturation of Y-zeolites with molybdenum carbonyl can produce catalysts with high molybdenum dispersion (ref.6, 7). Subsequent sulfidation of these catalysts leads toward highly dispersed, supported sulfided molybdenum species (ref. 8,9) exhibiting high reactivity in HDS and water-gas shift reaction (ref. 9,10). 

In recent years, our laboratory has sought to apply Aese relationships in a qualitative to semi-quantitative way to transition metal electrode reactions characterize by large structural change. We also have sought to study compounds that are representative of transition elements in biological systems, smce mner-shell effects often have important consequences on reactivity in such systems. In Ae following sections we describe results for a number of metalloporphyrins [3] and for several complexes of Mo Aat model Ae behavior of Ais element m molybdenum-containmg enzymes [4]. 

It must also be noticed that generally tungsten hexachloride derived catalysts are reactive towards / -olefins, whereas molybdenum salts are most widely used with a-olefins. In each case however, the main observation to be made (as with heterogeneous catalysts) is that it is necessary to have a cocatalyst besides the transition metal salt. This fact must be taken in account where mechanistic studies are undertaken on the generation of the active species for these reactions. 

---