Iron-ammonia catalyst

Figure 7.21. Fraction of unoccupied sites, and of sites occupied by atomic nitrogen and NH, as a function of reactor length on a potassium-promoted iron ammonia catalyst at 673 K,...

However, the hydrogenation catalysts can be promoted also by compounds which are ineffective for the iron ammonia catalysts, e.g., by silica and silicates, silicofluorides, borates, and phosphates. An interesting type of hydrogenation catalysts was found in the form of zeolites which by ion exchange were impregnated with heavy metal salts. 

Kummer and Emmett 311) studied the chemisorption of carbon monoxide on an iron ammonia catalyst by the same method and found a partial mixing of the desorbed gas, as if the surface consisted of a heterogeneous complex of homogeneous parts. Similar results were obtained by Eischens 312). 

The chemisorption of nitrogen on an iron ammonia catalyst was also studied by Emmett and Kummer 313), who found that the surface behaved as if it were of a homogeneous character. 

The state of iron ammonia catalysts is dealt with in the following chapters, and x-ray, magnetic, and electric data will be discussed together with adsorption measurements. Information about the catalysts combined with kinetic experiments has led to a fairly good qualitative understanding of ammonia synthesis on iron catalysts, but owing to the extremely complicated nature of the catalyst surface during reaction, a quantitative treatment based on data of catalyst and reactants will not be attained in the near future. 

Three more experimental proofs for surface heterogeneity of iron ammonia catalysts will be mentioned. 

The presence of various active parts on the surface of the iron-ammonia catalyst was demonstrated by Emmett and Kummer (74) by means of adsorbing radioactive and nonradioactive samples of carbon... 

From a study of the mechanism of the poisoning action of water vapors mill oxygen on iron ammonia catalysts 21 and by making certain assumptions, Almquistsu has been able to calculate that in pure iron catalysts about one atom in two thousand is active toward ammonia synthesis, whereas in iron catalysts promoted by alumina about one atom in two hundred is active. This shows the remarkable added activity obtainable by the use of promoters. That the effect is complicated beyond any simple explanation is evidenced further by some of the results of Almquist and Black, These workers have shown that whereas an iron-alumina catalyst shows greater activity toward ammonia synthesis at atmospheric pressure than an iron catalyst containing both alumina and potassium oxide, the hitter catalyst is 50 per cent more active when the pressure is raised to 1(X) atmospheres. 

Selective chemisorption methods applied to Iron ammonia catalysts... 

Chemisorption of Nitrogen and Hydrogen It is generally agreed that at least one of the reactants of every catalytic reaction must be chemisorbed on to the catalyst surface. Such data were, therefore, taken on typical iron ammonia catalysts. Results show that three different types of chemisorption of hydrogen exist on a singly promoted iron catalyst type C ( ) in the temperature range -195 C to... 

In the pre-World War II days there was little work done at Princeton on synthesis of catalysts. Copper catalysts were made by reduction of Kahlbaum copper oxide, the iron ammonia catalysts were obtained from the Fixed Nitrogen Laboratory through the courtesy of Dr. Paul Emmett, the nickel on kleselguhr catalyst was obtained from DuPont. Platinum on asbestos was made in the laboratory by soaking asbestos with chloroplatinic acid and then igniting it, mixed chromite catalysts were precipitated and calcined and a study was made. 

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