Porous monolayer materials have been proven potential for gas separation and purification, because of their natural pathways of controllable sizes and well-ordered distribution. In this work, a novel material, two-dimensional (2D) porous polyphthalocyanine (PPc) is investigated by density functional theory (DFT) simulations for separating NH3 from H-2 and N-2 during ammonia synthesis process. Based on the calculated diffusion barriers through transition state search, we demonstrate that 2D PPc is able to offer high selectivity (107) of (H-2, N-2)/NH3 at room temperature. Further molecular dynamics (MD) simulation also indicates that the 2D PPc can effectively separate NH3 from H-2 and N-2. Thus the 2D PPc is promising for the practical applications of synthetic ammonia process. (C) 2017 Elsevier B.V. All rights reserved.