We present a combined density functional theory (DFT) and microkinetic modeling study of synthesis gas conversion on Cu and Ca modified Mo6S8 catalysts to value-added products. Our results show that CO* + H* -> HCO* + (H) -> H2CO* + (H) -> H3CO* + (H) -> CH3OH* -> CH3OH (g) is an optimal pathway on the Ca-Mo6S8 surface. With the combination of Energetic span model (ESM) and binding energy analysis, we conclude that Ca -Mo6S8 is a promising catalyst for formaldehyde and methanol from synthesis gas conversion. Meanwhile, the most energetically favorable outcome on the Cu-Mo6S8 surface is the production of ethanol. Microkinetics simulations are carried out on the basis of the first-principles data, which predict the synthesis gas conversion rate and the product distribution. This study demonstrates that introducing metal Cu or Ca into Mo6S8 will design high-performance catalysts with synergistic interactions for tuning selectivity. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.