Kinetics and mechanism of the ammonia synthesis

The reaction rate in stoichiometric mixtures of nitrogen and hydrogen or deuterium has been measured on two different doubly promoted iron catalysts, between 218 and 302 $^\circ$C, $\frac{1}{3}$ and 1 atm and over a 300-fold range of efficiencies. The kinetic data as well as the isotope effect indicate that the rate-determining step is the chemisorption of nitrogen on a surface mainly covered with NH radicals. The presence on the surface of NH radicals instead of nitrogen atoms opens new perspectives on the kinetics and mechanism of ammonia synthesis.