Due to the high protein content in algal species, these precursors require further catalytic removal of heteroatoms such as nitrogen, being upgraded to biofuels. In the current study, first, synthesis of Na(+)ZSM-5 nanocrystals with well-distribution in size was performed successfully with a novel technique in super-critical water. After converting to H(+)ZSM-5 type, it was applied for hydrodenitrogenation (HDN) of crude bio-oil, obtained from hydrothermal liquefaction (HTL) of chlorella sp. microalgae, in the presence of high temperature water and formic acid (HCOOH) mixture. The effects of reaction temperature (250-500 degrees C), formic acid as a source of in-situ hydrogen, and nano-catalyst (compared with industrial type) on nitrogen elimination and H/C ratio were investigated comprehensively. Compared with non-catalytic upgrading conditions, a substantial amount of nitrogen removal was obtained in the presence of nano-catalyst and formic acid with the maximum amount of 75 wt% at 400 degrees C in comparison with the macron-size industrial catalyst (54 wt%) at the same temperature. Due to more miscibility and consequently high degree of liquid fuel recovery (Y-liq) with less coking as well as more HDN, T = 400 degrees C was chosen as the optimum temperature. Furthermore, H/C ratio of upgraded bio-oil, as an index of aromatization, had similar trend which indicates that in the presence of H(+)ZSM-5, higher temperature is more favorable to aromatization than cracking which makes HDN more difficult. In the absence of a catalyst, H/C ratio showed no substantial trend with temperature which demonstrates the significance of H(+)ZSM-5 catalyst for cracking. (C) 2017 Elsevier Ltd. All rights reserved.