A novel synthesis route, using citric acid as a chelating agent, for the formation of gamma-Mo2N and pure phase of Ni2Mo3N catalysts and their application for NH3 decomposition reaction for clean hydrogen production, have been performed. Successful formation of a pure bulk phase of Ni2Mo3N was confirmed by using XRD, XPS, HRTEM techniques and found that Ni2Mo3N is not air sensitive. Ni2Mo3N catalyst showed very high catalytic activity for NH3 decomposition reaction having similar to 97% conversion of NH3 at 525 degrees C at 6000 h(-1) GHSV, better than previously reported results on any non-promoted, non-precious catalysts, which is mainly due to the formation of pure phase and high surface area for this catalyst using a chelating method of preparation. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.