Iron FeMo catalysts

Sellmann, D., Utz, J., Blum, N., and Heinemann, F. W. (1999) On the function of nitrogenase FeMo cofactors and competitive catalysts chemical principles, structural blue-prints, and the relevance of iron sulfur complexes for N2 fixation, Coord. Chem. Rev. 190-192, 607-627. 

Introduction of a support (i.e. Ti02) to these systems can induce positive effects on the active phase (FeMo), as to avoid an excessive sintering of the particles during the thermal treatment and/or modification of the reduction capacity and the acid properties. The synergy of iron molybdate and the support is therefore another way for improving the catalytic performance of these solids. Such benefitial effects have been detected in bismuth-molybdenum-titania mixed oxides prepared via sol-gel, in addition these solids resulted to be amorphous materials with a unique morphology and extraordinary dispersion of the active phase [12]. These results encouraged us to extend this field to iron molybdenum oxide catalysts. 

Since the binding site for N2 in the enzyme seems to be a rectangular array of four Fe atoms in the waist region of FeMo-co, perhaps the most relevant model system is Holland s four-iron complex. On reduction with the powerful reductant, KCg, N2 can be split into two coordinated nitrides as shown in Eq. 16.20. In the Haber process, N2 is believed to be split into two coordinated nitrides bound to the surface of the Fe catalyst, so there may be a mechanistic similarity with N2ase. 

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