A series of activated carbon (AC)-supported nickel phosphide catalysts were prepared; characterized using XRD, XPS, TEM, and NH3-TPD techniques; and evaluated for the deoxygenation of palmitic acid. The formation of Ni2P and/or Ni12P5 on the surface of AC could be controlled by controlling the Ni/P molar ratios. With low Ni/P molar ratios from 0.5 to 0.8, only crystalline Ni2P formed. Both Ni2P and Ni12P5 formed with Ni/P ratios of 1.0 and 1.5, whereas only Ni12P5 formed with a Ni/P ratio of 2.0. As the Ni/P ratio further increased (Ni/P >= 3.0), crystalline Ni formed in addition to Ni12P5. The deoxygenation activities of the NixP/AC catalysts were strongly dependent on the types and dispersion of the nickel phosphide. The oil yield and C-15 selectivity on the catalysts followed the sequence Ni1.5P/AC>Ni2.0P/AC>Ni1.0P/AC approximate to Ni3.0P/AC>Ni4.0P/AC>Ni0.5P/AC approximate to Ni0.8P/AC, Ni1.0P/AC> Ni1.5P/AC approximate to Ni0.8P/AC > Ni0.5P/AC approximate to Ni2.0P/AC > Ni3.0P/AC >Ni4.0P/AC, respectively. The high activity was attributed to the coexistence and high dispersion of Ni2P and Ni12P8, which were favorable for branched alkanes formation, C-15 selectivity improvement and oil yield increase. Due to the high-grade diesels (HV = 46.5 MJ kg(-1)) obtained, NixP/AC can be considered to be a very promising catalyst for transforming fatty acids into high-grade diesel. (C) 2016 Elsevier B.V. All rights reserved.