Surface Analysis of the Ammonia Synthesis Catalyst

It should be stressed that not only is there a pressure gap between the UHV studies and the high-pressure measurements, but also a material gap. The UHV studies use carefully cleaned iron metal in the form of single crystals as the catalyst. On the other hand, elemental polycrystalline iron without surface purification does not catalyze ammonia synthesis at high pressure (1 bar), as has been described in Section 2.2. This may be rationalized in terms of the extreme sensitivity of the 

A target of the work described below is the preparation of technical catalyst surfaces under in situ conditions. The state of nitrogen chemisorbed onto these surfaces will subsequently be characterized by X-ray photoelectron spectroscopy for comparison with the iron single-crystal studies. 

Since a technical catalyst surface cannot accurately be defined by a single term such as a clean iron surface, a large section of this work consists of the description of surfaces obtained by three different methods of activation. 

The following reduction procedures were applied. Direct observation of the reduction process was achieved by exposure of the samples inside the analysis chamber to hydrogen pressures of typically 1x10 mbar for ca 120 h, after which time the evolution of water was almost complete. 

In the following sections, results will be presented which have been obtained for two catalysts designated catalyst 1 and catalyst 2 and which were of the same nominal bulk composition given in Section 2.2. Despite significant differences in 

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