Rate equation and mechanism of ammonia synthesis at industrial conditions

The ammonia synthesis reaction has been studied over a wide range of conditions, including conditions of vital importance for industrial use of the process. A reactor with a good approach to isothermal conditions has been used. A digital computer was used to analyze the results. We find the Temkin-Pyzhev rate equation applicable in the range 370–495 °C and 150–310 atm. We realize that our kinetic data could hardly constitute a definite proof of a given reaction mechanism; however, they do confirm one mechanism out of a number of different ones. This mechanism has as its rate-determining step the chemisorption of nitrogen on a nonuniform surface on which is found as the main species chemisorbed nitrogen atoms. Somewhere between 370 °C and 330 °C there is a change in apparent energy of activation which may indicate a change in mechanism or surface coverage.