The influence of potassium addition on the structural, catalytic and surface properties of the cobalt molybdenum nitride was studied. The measurements of the catalytic activity and the specific surface area as well as the phase analysis with the use of X-ray diffraction were performed. The mixtures of Co3Mo3N and Co2Mo3N phases have been found to constitute the samples. The concentration ratio between the Co2Mo3N and Co3Mo3N phases is notably influenced by potassium admixture. The specific surface area of the catalysts changes also with the Co2Mo3N/Co3Mo3N ratio. The catalytic activity of the catalysts in the ammonia synthesis carried out at 400 degrees C and under the pressure of 10 MPa can be increased up to 2.4 times by the addition of potassium compounds. There is the optimal range of potassium concentration between 0.8 and 1.2 wt.%. (C) 2010 Elsevier B.V. All rights reserved.