The Cs-modified Co3Mo3N catalysts were successfully prepared by a facile single-step decomposition of a mixture containing hexamethylenetetramine (HMTA) and corresponding metal salts under the flow of nitrogen at 700 degrees C and their catalytic activity for ammonia decomposition was investigated. The Co3Mo3N phase was observed in the XRD pattern of as-prepared sample and acted as the active component for the reaction. The XPS analysis clarified the existence of Cs species, indicating that these species should be dispersed over Co3Mo3N. The addition of a small amount of Cs species significantly improved the catalytic performance of the Co3Mo3N catalyst. The further addition of Cs species had a negative effect on the catalytic activity for the reaction.(NH3)-N-15 isotopic studies revealed that the nitrogen species in Co3Mo3N were exchangeable with nitrogen atoms in gas phase, elucidating the mechanism of the reaction over the Co3Mo3N catalysts. The kinetics analysis indicated that the modification by a small amount of Cs species alleviated the negative effect of the hydrogen poisoning on the active sites of Co3Mo3N catalysts. The desorption behavior of hydrogen and nitrogen suggested that the Cs modification facilitated the recombinative desorption of hydrogen and nitrogen atoms from the active components, resulting in the improvement in the activity of Co3Mo3N. This improvement was due to the electronic modification of Co3Mo3N by the electron donation of Cs promoter. (C) 2017 Elsevier B.V. All rights reserved.