This study proposed a novel and facile approach to promote the stability of nickel phosphide (Ni2P) based catalysts by adding silica (SiO2) as structural promoter under hydrothermal condition. Catalytic hydrodeoxygenation (HDO) of triglyceride using soybean oil as model feed over Ni2P and palladium supported on alpha-Al2O3 (Ni2PPd/alpha-Al2O3) with and without SiO2 addition was conducted. With SiO2 modification, the catalyst was stable for 144 h which is three times of that from the unmodified one, while higher than 99.0 wt.% conversion was achieved with green diesel (i.e., C15-18 alkane) as the main products. H-2-TPD, NH3-TPD, and XRD over fresh catalysts proved that SiO2 addition exhibited no distinguished effect on hydrogen chemisorption ability and active phase. XRD, TEM, XPS, EDX, XRF, H-2-TPR, N-2 physisorption, and TG/IR over fresh or/and spent catalysts demonstrated that SiO2 was a structural stability promoter (spacer), hindering the transformation of the active phase Ni2P. Furthermore, carbon deposition during the HDO process due to exist of metallic nickel was reduced with SiO2 addition. This work demonstrated that Ni2P supported on alpha-Al2O3 modified by SiO2 (Ni2PPd-SiO2/alpha-Al2O3) was a promising catalyst for the hydrodeoxygenation (HDO) of triglyceride to produce green diesel. With further work, it may lead to a catalyst capable for HDO in industry. (C) 2017 Elsevier Ltd. All rights reserved.