Zirconium ammonia synthesis

First attempts to check this hypothesis [23] revealed a superior catalytic activity of iron in amorphous iron-zirconium alloys in ammonia synthesis compared to the same iron surface exposed in crystalline conventional catalysts. A detailed analysis of the effect subsequently revealed that the alloy, under catalytic conditions, was not amorphous but crystallized into platelets of metastable epsilon-iron supported on Zr-oxide [24, 25]. 

Figure 8. SEM surface images of partly crystallized sections of an activated Fe Zr alloy used for ammonia synthesis [23, 24J The main image reveals the formation of a stepped iron metal structure with a porous zirconium oxide spacer structure An almost ideal transport system for gases into the interior of the catalyst is created with a large metal-oxide interface which provides high thermal and chemical stability of this structure The edge contrast in the 200 keV backscatlered raw data image arises from the large difference in emissivity between metal and oxide It is evident that only fusion and segregation-crystallization can create such an interface structure.

Notable progress in ammonia synthesis has also been made by Chirik and coworkers, who have shown that ammonia can be evolved from a zirconium metallocene complex. Using a tetramethylated-bis-Cp-dichloride complex, they were able to first add N2 to form a dimeric Zr complex and subsequently add excess H2, with heating, to evolve ammonia [99]. Their work, though not catalytic, also provides basic mechanistic insights into transition-metal-mediated N-H bond catalysis. 

Ammonia synthesis catalysts containing iron, potassium, and zirconium oxides, and cobalt and magnesium ferrites. P. D. Rabina, V. S. Komarov, and M. D. Efros. SU 539601 (1977). 

Tetrakis(hexafluoroisopropoxides) of titanium, zirconium, and hafnium have been prepared by the reaction of sodium hexafluoroisopropoxide in an excess of hexafluoroisopropyl alcohol with the anhydrous metal chloride, and the spectroscopic properties are reported. The authors note that, in their experience, application to the Group IV transition metals of the previously published method for metal hexafluoroisopropoxide synthesis gives poor yields of material containing metal, fluorinated alkoxides, and co-ordinated ammonia. Dehydration of the hydrated metal chloride with methyl orthoformate and addition of hexafluoroisopropyl alcohol, followed by passage of dry ammonia through the solution, gives satisfactory yields for yttrium, lanthanum, neodymium, and erbium. 

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