The role of potassium in the catalytic synthesis of ammonia

A model study on the promotor action of K in the synthesis of ammonia on iron catalysts was performed by studying the influence of preadsorbed potassium on the rate of dissociative nitrogen chemisorption (which is the rate-limiting step) on a Fe(100) single crystal surface. It was found that a concentration of 1.5 × 1014 K atoms/cm2 increases this rate by a factor of about 300 at 430 K and removes also the activation energy for this process. This effect is attributed to the increased adsorption energy of molecular N2 (11.5 kcal/mole) which is related with the pronounced transfer of electronic charge from K to the Fe surface.