Rhenium catalysts, ammonia synthesis

It was found during studies of ammonia synthesis on iron that the incorporation of a condenser downstream of the sample valve in the external circulation loop of the HPLP apparatus (Fig. 7), enabled the system to be run as a flow rather than a batch reactor. This is true for any reaction system where the reactants are more volatile than the products, since the condenser temperature can be adjusted to trap the products almost exclusively, allowing a nearly pure stream of reactants to impinge on the catalyst. In the case of ammonia synthesis, (where, next to the product, nitrogen at a partial pressure of 5 atm was the most condensable species) a slurry of isopentane (— 159.9 °C) was found to be the ideal condenser medium. During a study of rhenium-catalyzed ammonia synthesis the isopentane condenser was switched in periodically to reduce the ammonia partial pressure to below that at which it appeared to poison the catalyst. In this way, the rhenium was able to produce ammonia in excess of the amount usually leading to poisoning. 

From the viewpoint of competitive adsorption we can consider as well the sorption of precursors upon the synthesis of Pt-Be/Al203 catalysts from H2PtCl3 and rhenium acid [4] and of Pt-Ru/ 02 catalysts from the ammonia complexes of Pt and Ru [5]. In both cases precursors were in the same ionic form and adsorbed on the same sites. 

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