PATENTS

       21.            ANDERSON, R. R., AND SCHULTZ, J. F. Iron Nitride Catalysts in Carbon Oxide Hydrogenations.  United States Patent 2,620,728.  Fe. 24, 1953: appl. Filed Aug. 22, 1949, Serial No. 111,755: 15 claims (Cl. 260-449.6).

The most practical method for formation of nitrified Fe catalysts has been found to be treatment of reduced Fe catalyst in a relatively rapid stream of NH₃ gas at elevated temperature.  The reaction is expressed as:

S Fe+NH₃=2 Fe₄N+3 H₂

6 Fe₄N+2 NH₃=3 Fe₃+3 H₂

The formation of the nitride depends upon the ratio of the concentration of NH₃: H₂ at the surface of the Fe. Or the formation of the nitride depends on the ratio of the square of the partial pressure of NH₃ to the cube of the partial pressure of H₂³.

P NH₃²: p H₂³.

For any given temperature, there is a ratio of concentration of NH₃: H₂ below which it is thermodynamically impossible for either or both reactants to proceed at all.  The concentration of NH₃ necessary to form a nitride decreases with increase in temperature.  The practical temperature range is 200°-550° C.  Increasing the flow of NH₃ over the catalyst being nitrided will improve the rate and completeness of nitriding by increasing the NH3 concentration.  Above 550° C. the rate of nitriding is not improved by increasing the velocity of flow, because above this temperature the rate of decomposition of NH₃ is very rapid.  At temperatures below 200° C., although the rate of decomposition of NH₃ in the presence of Fe is virtually negligible, the rate of formation of the nitride is extremely slow.  Substantially 100% NH3 should be used.  Nitriding an Fe catalyst markedly increases its activity, particularly in the case of the fused Fe catalyst.  It gives the catalyst longer life and increases resistance to deposition of free C within the catalyst granules.  The catalyst expands during nitriding and does not change in volume during use in the synthesis.  It resists oxidation during use.  Nitriding of the catalyst tends to shift the distribution the distribution of products toward those of lower molecular weight and to increase the fraction of oxygenated compounds.  The higher the degree of nitriding, the greater the shift in distribution of products.  3 literature refs, and 3 United States patents cited.

ANDREWS. H. J., JR.  See abs. 2762.

ANDREW, T. See abs. 3938.