EXTRAPOLATION OF THE KINETICS OF MODEL AMMONIA-SYNTHESIS CATALYSTS TO INDUSTRIALLY RELEVANT TEMPERATURES AND PRESSURES

The elementary kinetics involed in the published low coverage ammonia synthesis potential energy diagram have been extrapolated by calculation, to industrially relevant temperatures (approximately 723 K) and pressures ( greater than 100 atmospheres) where it has been found that the rates of ammonia synthesis predicted by it are 10**5 times too low. The problem is that the reported nitrogen atom well depth is too great (even in the presence of potassium promoter) so that the prediction of the kinetics is to a totally nitrided iron surface. Correspondence between experiment and prediction is achieved, however, when this well depth is reduced, by requiring dissociation of the molecularly held nitrogen precursor state to be activated.